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Page 1

M850-00

T850 Series II

Base Station Equipment

400-520MHz

Service Manual

Issue 200

October 1998

M850-00-200

Page 2

M850-00

T800

Head Office New Zealand

Tait Electronics Ltd 558 Wairakei Road P.O. Box 1645 Christchurch New Zealand Phone: 64 3 358-3399 Fax: 64 3 358-3903

Radio Systems Division

535 Wairakei Road P.O. Box 1645 Christchurch New Zealand Phone: 64 3 358-1069 Fax: 64 3 358-6486

Australia

Tait Electronics (Aust) Pty Ltd 186 Granite Street Geebung Queensland 4034 P. O . B ox 6 79 Virginia Queensland 4014 Australia Phone: 61 7 3865-7799 Toll Free: 1800 077-112 Fax: 61 7 3865-7990

Canada

Tait Mobile Radio Inc. Unit 5, 158 Anderson Avenue Markham Ontario L6E1A9 Canada Phone: 1 905 472-1100 Toll Free: 1 800 890-8248 Fax: 1 905 472-5300

France

Tai t Fr an ce Sa r l 2 Avenue de la Cristallerie 92 316 Sèvres, Cedex France Phone: 33 1 41 14-05-50 Fax: 33 1 41 14-05-55

Germany

Tait Mobilfunk GmbH Willstätterstraße 50 D-90449 Nürnberg 60 Germany Phone: 49 911 96 746-0 Fax: 49 911 96 746-79

Hong Kong

Tait Mobile Radio (HK) Ltd Unit 2216 North Tower Concordia Plaza No. 1, Science Museum Road Tsim Sha Tsui East Kowloon Hong Kong Phone: 852 2369-3040 Fax: 852 2369-3009

New Zealand

Tait Communications Ltd Unit 4, 75 Blenheim Road P. O. Bo x 11 85 Christchurch Phone: 64 3 348-3301 Fax: 64 3 343-0558

Ta i w a n

Tait Mobile Radio (Taiwan) Ltd 1104, No. 142 Chung Hsiao E. Rd Sec. 4 Ta ip e i Ta iw a n Phone: 886 2 2731-1290 Fax: 886 2 2711-6351

Thailand

Tait Mobile Radio Ltd 14/1 Suwan Tower Ground Floor Soi Saladaeng 1 North Sathorn Road Bangrak Bangkok 10500 Thailand Phone: 662 267-6290-2 Fax: 662 267-6293

United Kingdom

Tait Europe Ltd Ermine Business Park Ermine Road Huntingdon Cambridgeshire PE18 6YA United Kingdom Phone: 44 1480-52255 Fax: 44 1480-411996

USA

Tait Electronics (USA) Inc. 9434 Old Katy Road Suite 110 Houston Texas 77055 USA Phone: 1 713 984-8684 Toll Free: 1 800 222-1255 Fax: 1 713 468-6944

Beijing

Tait Mobile Radio (HK) Ltd Beijing Representative Office Room 812, Tower A Beijing Bright China Chang An Building No. 7 Jianguomennei Dai Jei Dongcheng District Beijing China 100005

Singapore

Tait Electronics (Far East) Pte Ltd 4 Leng Kee Road SIS Building #05-11A Singapore 159088 Phone: 65 471-2688 Fax: 65 479-7778

31/09/98 Copyright TEL

Page 3

M850-00

About This Manual

Scope This manual contains general, technical and servicing informa-

tion on T850 Series II 25W, 50W and 100W base stations which comprise the following equipment:

25W base station T855 receiver

T856 25W transmitter

50W base station T855 receiver

T857 exciter T858 50W power amplifier

100W base station T855 receiver

T857 exciter T859 100W power amplifier

Format We have published this manual in a ring binder so that "revision

packages" containing additional information pertaining to new issues of PCBs can be added as required.

Revision Packages Revision packages will normally be published to coincide with

the release of information on a new PCB, and may also contain additions or corrections pertaining to other parts of the manual.

You may order as many packages as you require from your local Tait Dealer or Customer Service Organisation. Revision packages are supplied ready-punched for inclusion in your manual.

Revision Control Each page in this manual has a date of issue. This is to comply

with various Quality Standards, but will also serve to identify which pages have been updated and when. Each page and its publication date is listed in the "List of Effective Pages", and a new list containing any new/revised pages and their publication dates will be sent with each revision package.

Any portion of text that has been changed is marked by a vertical line (as shown at left) in the outer margin of the page. Where the removal of an entire paragraph means there is no text left to

mark, an arrow (as shown at left) will appear in the outer margin. The number beside the arrow will indicate how many paragraphs have been deleted.

The manual issue and revision status are indicated by the last three digits of the manual product code. These digits start at 200 and will increment through 201, 202, 203, etc., as revision packages are published, e.g:

2 0 3

issue status revision status

Thus, issue 203 indicates the third revision to issue 2 and means that three packages should have been added to the manual. The

Page 4

issue digit will only change if there is a major product revision, or if the number of revision packages to be included means that the manual becomes difficult to use, at which point a new issue manual will be published in a new ring binder.

PCB Information PCB information is provided for all current issue PCBs, as well

as all previous issue PCBs manufactured in production quantities, and is grouped according to PCB. Thus, you will find the parts list, grid reference index (if necessary), PCB layouts and circuit diagram(s) for each individual PCB grouped together.

Errors If you find an error in this manual, or have a suggestion on how

it might be improved, please do not hesitate to contact Customer Support, Radio Systems Division, Tait Electronics Ltd, Christchurch, New Zealand (full contact details are on page 2).

M850-00

Updating Equipment And Manuals

In the interests of improving performance, reliability or servicing, Tait Electronics Ltd reserve the right to update their equipment and/or manuals without prior notice.

Copyright

All information contained in this manual is the property of Tait Electronics Ltd. All rights are reserved. This manual may not, in whole or part, be copied, photocopied, reproduced, translated stored or reduced to any electronic medium or machine readable form without prior written permission from Tait Electronics Ltd.

Ordering Tait Service Manuals

You can order additional copies of this service manual from your nearest Tait Dealer or Customer Service Organisation. When ordering, make sure you quote the correct Tait product code ("M" number).

Publication Information

T850 Series II Service Manual Issue 200 published October 1998 Product Code M850-00-200

31/09/98 Copyright TEL

Page 5

M850-00

This manual is divided into nine parts as listed below, with each part being further subdivided into sections. There is a detailed table of contents at the start of each part and/ or section.

Part Title

A Introduction To Servicing

B T855 Receiver

C T856 Transmitter & T857 Exciter

D T858 & T859 Power Amplifiers

E T850 VCO PCB Information

F Installation

G System Configurations

H T800 Ancillary Equipment

I Using T850 Series II Equipment In A Series I Rack Frame

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List Of Effective Pages

The total number of pages in this Manual is 440, as listed below.

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M850-00

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Part A Introduction To Servicing

This part of the manual is divided into the sections listed below. These sections provide some general and advisory information on servicing procedures, and a brief history of PGM800Win programming software.

Section Title Page

1.1

1.2

1.3

1.4

2.1

2.2

2.3

2.3.1

2.3.2

2.4

3.1

3.1.1

3.1.2

3.2

General

Additional Technical Information Caution: CMOS Devices Caution: Aerial Load Caution: Beryllium Oxide & Power Transistors

Mechanical

Torx Recess Head Screws Pozidriv & Philips Recess Head Screws Disassembly/Reassembly

Receivers/Exciters/Transmitters Power Amplifiers

Cover Screw Torques

Component Replacement

Leaded Components

Desoldering Iron Method Component Cutting Method

Surface Mount Devices

1.1

1.2

2.1

2.2

2.3

3.1

3.2

3.3

4.1

4.2

Cased Mica Capacitors

Software History

PGM800Win V1.0 PGM800Win V2.00

Figure Title Page

1.1

1.2

2.1

2.2

Typical Product Code & Serial Number Labels Typical Anti-static Bench Set-up Torx Screw Identification Pozidriv & Philips Screw & Screwdriver Identification

3.2

4.1

1.1

1.2

2.1

2.2

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General

A1.1

1 General

1.1 Additional Technical Information

If you have any questions about this manual or the equipment it describes, please contact your nearest Tait Dealer or Customer Service Organisation. If necessary, you can get additional technical help from Customer Support, Radio Systems Division, Tait Electronics Ltd, Christchurch, New Zealand (full contact details are on page 2).

When requesting information, please quote either the manual product code (e.g. M850-00-200), or the equipment product code and serial number which are printed on a label on the back of the product (as shown in Figure 1.1).

this area used for regional Type Approval information

T838-10-0000

Rev 1

900000

Tait Electronics Limited Made in New Zealand

Figure 1.1 Typical Product Code & Serial Number Labels

product code serial number

T835-10-0000 Rev 1

Tait Electronics Limited Made in New Zealand

900000

If you require information about a particular PCB, please quote the full PCB internal part number (IPN) which is screen printed onto the top side of the board (refer to the appropriate PCB Information section in this manual for more details).

1.2 Caution: CMOS Devices

This equipment contains CMOS Devices which are susceptible to damage from static charges. Care when handling these devices is essential. For correct handling procedures refer to the manufacturers' data books, e.g. Philips data books covering CMOS devices, or Motorola CMOS data books, Section 5 'Handling', etc.

An anti-static bench kit (refer to Figure 1.2) is available from Tait Electronics Ltd under the following product codes:

• KS0001 - 1 conductive rubber bench mat

- 1 earth lead to connect the mat to ground

• KS0004 - 1 wrist strap.

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A1.2

General

M850-00

conductive

wrist strap

to building earth (not mains earth)

Figure 1.2 Typical Anti-static Bench Set-up

1.3 Caution: Aerial Load

conductive rubber

bench mat

The equipment has been designed to operate safely under a wide range of aerial loading conditions. However, we strongly recommend that the transmitter should always be operated with a suitable load to prevent damage to the transmitter output power stage.

1.4 Caution: Beryllium Oxide & Power Transistors

The RF power transistors in current use all contain some beryllium oxide. This substance, while perfectly harmless in its normal solid form, can become a severe health hazard when it has been reduced to dust. For this reason the RF power transistors should not be broken open, mutilated, filed, machined, or physically damaged in any way that can produce dust particles.

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Page 17

M850-00

Mechanical

A2.1

2 Mechanical

2.1 Torx Recess Head Screws

Torx recess head screws are becoming the standard screw head type in all T800 Series II equipment, with Pozidriv and Philips recess head screws being used in fewer applications.

The Torx recess head has the advantage of improved screwdriver tip location, reducing the chances of screw head damage caused by the driver tip rotating within the recess. In addition, using a ball-tip Torx screwdriver allows you to drive a Torx head screw with the driver on a slight angle, which can be useful in situations where access is restricted.

It is important that you use the correct Torx screwdriver tip:

M3 screws - T10 M4 screws - T20.

Figure 2.1 below shows a typical Torx recess head screw (actual hardware may differ slightly from this illustration due to variations in manufacturing techniques).

"star" shaped recess with six internal notches

Figure 2.1 Torx Screw Identification

Page 18

A2.2

Mechanical

M850-00

2.2 Pozidriv & Philips Recess Head Screws

Pozidriv and Philips recess head screws will continue to be used in T800 Series II equipment in a few special applications. It is important that you use the correct type and size screwdriver for each screw type to avoid damaging the screw head.

It is particularly important that you do not use Philips screwdrivers on Pozidriv screw heads as the tapered driving flutes of the Philips screwdriver do not engage correctly with the parallel-sided slots in the Pozidriv screw head. This can result in considerable damage to the screw head if the screwdriver tip turns inside the recess.

Note:

If you find you need excessive downwards pressure to keep the screwdriver tip in the Pozidriv screw head, you are probably using the wrong type and/ or size screwdriver.

Figure 2.2 below shows the main differences between typical Pozidriv and Philips screw heads and screwdriver tips (actual hardware may differ slightly from these illustrations due to variations in manufacturing techniques).

Pozidriv Philips

internal notches

no special markings

"star" markings between slots

slots with parallel sides

slots with tapered sides

driving flutes with parallel sides

driving flutes with tapered sides

ridges between driving flutes

Figure 2.2 Pozidriv & Philips Screw & Screwdriver Identification

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M850-00

Mechanical

A2.3

2.3 Disassembly/Reassembly

2.3.1 Receivers/Exciters/Transmitters

To carry out alignment or change option links, you need to remove only the top cover, i.e. the one adjacent to the front panel handle and on the opposite side to the main D-range connector (D-range 1/PL100).

You need to remove the bottom cover to:

• access transmitter RF power transistors and many SMD components

• change solder blob links

• fit test leads to circuit block access points.

2.3.2 Power Amplifiers

You should carry out the tuning and power output level setting procedures with the cover on.

2.4 Cover Screw Torques

Receivers/Exciters/Transmitters .. 1.36Nm/12lb-in.

Power Amplifiers .. 0.9Nm/8lb-in.

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A2.4

Mechanical

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Component Replacement

A3.1

3 Component Replacement

3.1 Leaded Components

Whenever you are doing any work on the PCB that involves removing or fitting components, you must take care not to damage the copper tracks. The two satisfactory methods of removing components from plated-through hole (PTH) PCBs are detailed below.

Note:

The first method requires the use of a desoldering station, e.g. Philips SBC 314 or Pace MBT-100E.

3.1.1 Desoldering Iron Method

Place the tip over the lead and, as the solder starts to melt, move the tip in a circular motion.

Start the suction and continue the movement until 3 or 4 circles have been completed.

Remove the tip while continuing suction to ensure that all solder is removed from the joint, then stop the suction.

Before pulling the lead out, ensure it is not stuck to the plating.

If the lead is still not free, resolder the joint and try again.

Note:

The desoldering iron does not usually have enough heat to desolder leads from the ground plane. Additional heat may be applied by holding a soldering iron on the tip of the desoldering iron (this may require some additional help).

3.1.2 Component Cutting Method

Cut the leads on the component side of the PCB.

Heat the solder joint out from the component side: do

Fill the hole with solder and then clear with solderwick.

sufficiently

to allow

not

easy

use undue force.

removal of the lead by drawing it

Page 22

A3.2

Component Replacement

3.2 Surface Mount Devices

M850-00

Caution:

Surface mount devices (SMDs) require special storage, handling, removal and replacement techniques. This equipment should be serviced only by an approved Tait Dealer or Customer Service Organisation equipped with the necessary facilities. Repairs attempted with incorrect equipment or by untrained personnel may result in permanent damage. If in doubt, contact your nearest Tait Dealer or Customer Service Organisation.

3.3 Cased Mica Capacitors

Cased mica capacitors can be removed by heating the top with a heavy-duty soldering iron and gently lifting the capacitor off the PCB with a solder-resistant spike or equivalent.

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Software History

A4.1

4 Software History

28/06/96 PGM800Win Version 1.0 18/08/97 PGM800Win Version 2.00

4.1 PGM800Win V1.0

PGM800Win V1.0 is different in concept from DOS versions of PGM800 in that it is Win-

dows PGM800.

The major changes are outlined below:

based. It also includes many new and improved features over DOS versions of

• The Windows

• PGM800Win includes several new radio models which are not programmable with DOS versions of PGM800.

• Out of range frequencies will result in warning messages and will not be accepted for entry into the standard library module. User defined modules can be created, however, allowing variation from the standard library module.

• Channel numbers default to 0-127 to match the EPROM memory locations. However, the user can change this setting so that the channel numbers run from 1-128 to suit his/her particular needs.

Note:

The data files produced by BASEPROG V1.0 and all DOS versions of PGM800 are still compatible with PGM800Win V1.0.

 environment makes data entry and editing significantly easier.

4.2 PGM800Win V2.00

PGM800Win V2.00 is an upgraded and expanded version of PGM800Win V1.0. It has been developed specifically for T800 Series II base stations, but retains the ability to program Series I equipment.

The major changes are outlined below:

• PGM800Win V2.0 will program T800 Series II base station modules via serial communications.

• Deviation and reference modulation settings are written automatically to the radio.

1. Windows is a registered trademark of the Microsoft Corporation.

Page 24

A4.2

• Extra information that is not stored in the radio (but which is still relevant to the

Software History

radio) can be saved to a file on disk (e.g. note field, auxiliary pin names, etc.).

M850-00

Note:

The data files produced by BASEPROG V1.0, all DOS versions of PGM800, and PGM800Win V1.0 are still compatible with PGM800Win V2.00.

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Part B T855 Receiver

This part of the manual is divided into six sections, as listed below. There is a detailed table of contents at the start of each section.

Section Title

1 General Information

2 Circuit Operation

3 Initial Tuning & Adjustment

4 Functional Testing

5 Fault Finding

6 PCB Information

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BII

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T855 General Information

B1.1

1 T855 General Information

This section provides a brief description of the T855 receiver, along with detailed specifications and a list of types available.

The following topics are covered in this section.

Section Title Page

1.1 Introduction 1.5

1.2

1.2.1

1.2.2

1.2.3

1.2.4

1.2.4.1

1.2.4.2

1.2.4.3

1.2.5

1.2.6

1.2.6.1

1.2.6.2

1.2.6.3

1.3 Product Codes 1.12

1.4 Standard Product Range 1.13

Specifications

Introduction General RF Section Audio Section

General CTCSS

Mute Operation Microprocessor Controller Test Standards

European Telecommunication Standard (ETS) DTI CEPT Recommendation T/R-24-01 Telecommunications Industry Association

1.6

1.7

1.9

1.10

1.11

Figure Title Page

1.1

1.2

T855 Main Circuit Block Identification T855 Front Panel Controls

1.4

Page 28

B1.2

T855 General Information

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T855 General Information

replace A4 pages B1.3/B1.4 with A3 pages B1.3/B1.4

B1.3

Page 30

B1.4

T855 General Information

replace A4 pages B1.3/B1.4 with A3 pages B1.3/B1.4

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1.1 Introduction

T855 General Information

B1.5

The T855 is a high performance microprocessor controlled FM base station receiver designed for single or multichannel operation in the 400 to 530MHz frequency range

The receiver is a dual conversion superhet with a synthesised local oscillator. The first IF is 45.0MHz, allowing exceptionally high spurious signal rejection to be achieved in the receiver front end. The second IF section (455kHz) combines amplitude limiting, detection and audio preamplification within a single integrated circuit. It also drives carrier and noise level detectors for signal strength indication and gating the audio output. RSSI can be used to drive a carrier mute for audio output gating (link selectable) when the optional T800-04-0000 RSSI PCB is fitted.

The audio section output can be adjusted to deliver >+10dBm to a 600 ohm balanced output, and 1W to a local monitor speaker. A flat or de-emphasised audio response is link selectable.

The synthesiser frequency is programmed via the serial communications port. Eight channel select lines are accessible via an additional D-range connector (D-range 2 T800-03-0000) at the rear of the set.

All components except those on the VCO board are mounted on a single PCB. This is secured to a die-cast chassis which is divided into compartments to individually shield each section of circuitry. Access to both sides of the main PCB is obtained by removing each of the two chassis covers. There is provision within the chassis to mount small option PCBs.

The front panel controls include gating sensitivity, line level, monitor volume and a monitor mute switch.

The T855 has a width of 60mm and occupies a single space in a Tait rack frame, which has the ability to accommodate up to seven standard modules.

1. Although capable of operating over the 400-530MHz frequency range, the T855 has a 5MHz switching range (see Section 1.2.3 and Section 3.1).

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B1.6

T855 General Information

M850-00

1.2 Specifications

1.2.1 Introduction

The performance figures given are minimum figures, unless otherwise indicated, for equipment tuned with the maximum switching range and operating at standard room temperature (+22°C to +28°C) and standard test voltage (13.8V DC).

Where applicable, the test methods used to obtain the following performance figures are those described in the EIA and ETS specifications. However, there are several parameters for which performance according to the CEPT specification is given. Refer to Section 1.2.6 for details of test standards.

Details of test methods and the conditions which apply for Type Approval testing in all countries can be obtained from Tait Electronics Ltd.

The terms "wide bandwidth", "mid bandwidth" and "narrow bandwidth" used in this and following sections are defined in the following table.

Channel Spacing

Wide Bandwidth 25kHz ±5.0kHz 15.0kHz

Mid Bandwidth 20kHz ±4.0kHz 12.0kHz

Narrow Bandwidth 12.5kHz ±2.5kHz 7.5kHz

Sensitivity and distortion figures are stated for standard operating conditions which includes audio de-emphasis. Note that the sensitivity and distortion figures will be degraded when flat audio is selected.

Link PL210

De-emphasised Audio 1-2 (A-B) 2-3 (E-F)

Flat Audio 2-3 (B-C) 1-2 (D-E)

a. The letters in this column refer to the identification letters screen printed onto the PCB be-

side each set of links.

Modulation

100% Deviation

Receiver

IF Bandwidth

Link PL220

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Page 33

M850-00

1.2.2 General

T855 General Information

B1.7

Number Of Channels .. 128 (standard)

Supply Voltage:

Operating Voltage .. 10.8 to 16V DC Standard Test Voltage .. 13.8V DC Polarity .. negative earth only Polarity Protection .. diode

Supply Current:

Standby .. 350mA Full Audio .. 750mA

Operating Temperature Range .. -20°C to +60°C

Dimensions:

Height .. 191mm Width .. 60mm Length .. 324mm

Weight .. 2.13kg

1.2.3 RF Section

Frequency Range .. 400-530MHz

Type .. dual conversion superheterodyne

Frequency Increment .. 5 or 6.25kHz

Switching Range .. 5MHz (i.e. ±2.5MHz from the centre

frequency)

Input Impedance .. 50 ohms Frequency Stability .. ±1ppm, -20°C to +60°C

(see also Section 1.4)

Signal Strength Indicator .. -115dBm to -70dBm, 0 to 5V (RSSI optional) at approx. 10dB/V

1. Additional channels may be factory programmed. Contact your nearest Tait Dealer or Customer Service Organisation.

Page 34

B1.8

IF Amplifiers:

Sensitivity (De-emphasised Response):

Sensitivity (Flat Response):

Signal+Noise To Noise Ratio (Typical):

T855 General Information

Frequencies .. 45MHz and 455kHz Bandwidths-

Narrow Bandwidth (NB) .. 7.5kHz Mid Bandwidth (MB) .. 12kHz Wide Bandwidth (WB) .. 15kHz

Single Channel .. -117dBm Bandspread (12dB Sinad) .. -115dBm (across switching range)

Single Channel .. -111dBm Bandspread (12dB Sinad) .. -109dBm

De-emphasised

RF Level -107dBm .. 30dB (WB) 20dB (WB)

25dB (NB) 15dB (NB)

M850-00

Flat

RF Level -83dBm (CEPT) .. 54dB (MB) 49dB (MB)

50dB (NB) 45dB (NB)

RF Level -57dBm (EIA) .. 55dB (WB) 55dB (WB)

Selectivity:

Narrow Bandwidth (±12.5kHz) .. 83dB minimum, 85dB typical (CEPT) Mid Bandwidth (±20kHz) .. 87dB minimum, 90dB typical (CEPT) Wide Bandwidth (±25kHz) .. 87dB minimum, 90dB typical (CEPT)

Offset Selectivity (Canada only) .. 20dB

Spurious Response Attenuation .. 100dB

Intermodulation Response Attenuation:

Narrow Bandwidth .. 80dB CEPT (typical) Mid Bandwidth .. 75dB CEPT Wide Bandwidth .. 85dB EIA

Blocking .. 100dB

Co-channel Rejection .. 6dB

Amplitude Characteristic .. 3dB

Spurious Emissions:

Conducted .. -90dBm to 4GHz Radiated .. -57dBm to 1GHz

-47dBm to 4GHz

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M850-00

T855 General Information

1.2.4 Audio Section

1.2.4.1 General

Outputs Available .. line and monitor

Frequency Response .. flat or de-emphasised (750µs)

(link selectable)

Flat Response:

Bandwidth .. 67 to 3400Hz Response .. within +1, -2dB of output level

at 1kHz

De-emphasised Response:

Bandwidth .. 300 to 3400Hz Response .. within +1, -3dB of a -6dB/octave

de-emphasis characteristic (ref. 1kHz)

B1.9

Line Output:

Power .. adjustable to >+10dBm Load Impedance .. 600 ohms Distortion (@ -70dBm signal level):

De-emphasised

Wide Bandwidth .. ≤2% ≤2% Mid & Narrow Bandwidth .. ≤2% ≤4%

1.2.4.2 CTCSS

Linkable High Pass Filter:

Bandwidth .. 350 to 3400Hz Response .. within +1, -3dB of level at 1kHz Hum And Noise .. 30dB min. at 250.3Hz (1kHz at 60% system deviation 35dB typical (67 to 240Hz) CTCSS at 10% system deviation)

Tone Detect:

Tone Squelch Opening .. better than 6dB sinad

3dB sinad at 250.3Hz (typical) 4dB sinad at 100Hz (typical)

Flat

Tone Detect Bandwidth .. ±2.1Hz accept (typical)

±3.0Hz reject (typical)

Response Time .. 150ms open and close (typical)

Page 36

B1.10

1.2.4.3 Mute Operation

Systems Available .. noise mute and carrier mute

Noise Mute:

Carrier Mute (Optional):

T855 General Information

Operating Range .. 6-20dB sinad Hysteresis .. 1.5 to 6dB Threshold .. adjustable to -105dBm Opening Time .. 20ms Closing Time .. 50ms

Operating Range .. -115 to -80dBm Hysteresis .. 2 to 10dB Opening Time .. 5ms Closing Time .. 50ms

M850-00

Note:

The opening and closing times given above are for the standard setup (SL210 linked and SL220 not linked - refer to Section 3.8).

1.2.5 Microprocessor Controller

Auxiliary Ports:

Open Drain Type .. capable of sinking 2.25mA via 2k2Ω

max. .. 5V

1.2.6 Test Standards

Where applicable, this equipment is tested in accordance with the following standards.

1.2.6.1 European Telecommunication Standard

ETS 300 086 January 1991

Radio equipment and systems; land mobile service; technical characteristics and test conditions for radio equipment with an internal or external RF connector intended primarily for analogue speech.

ETS 300 113 March 1996

Radio equipment and systems; land mobile service; technical characteristics and test conditions for radio equipment intended for the transmission of data (and speech) and having an antenna connector.

ETS 300 219 October 1993

Radio equipment and systems; land mobile service; technical characteristics and test conditions for radio equipment transmitting signals to initiate a specific response in the receiver.

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Page 37

M850-00

ETS 300 279 February 1996

Radio equipment and systems; electromagnetic compatibility (EMC) standard for private land mobile radio (PMR) and ancillary equipment (speech and/or non-speech).

1.2.6.2 DTI CEPT Recommendation T/R-24-01

Annex I: 1988

Technical characteristics and test conditions for radio equipment in the land mobile service intended primarily for analogue speech.

Annex II: 1988

Technical characteristics of radio equipment in the land mobile service with regard to quality and stability of transmission.

1.2.6.3 Telecommunications Industry Association

T855 General Information

B1.11

ANSI/TIA/EIA-603-1992

Land mobile FM or PM communications equipment measurement and performance standards.

Page 38

B1.12

T855 General Information

M850-00

1.3 Product Codes

The three groups of digits in the T850 Series II product code provide information about the model, type and options fitted, according to the conventions described below.

The following explanation of T850 Series II product codes is not intended to suggest that any combination of features is necessarily available in any one product. Consult your nearest Tait Dealer or Customer Service Organisation for more information regarding the availability of specific models, types and options.

Model

The Model group indicates the basic function of the product, as follows:

T85X

-XX-XXXX T855 receiver T856 25W transmitter T857 exciter T858 50W power amplifier T859 100W power amplifier

Type

The Type group uses two digits to indicate the basic RF configuration of the product.

The first digit in the Type group designates the frequency range: T85X-X

The second digit in the Type group indicates the channel spacing: T85X-XX

X-XXXX ’1’ for 400-440MHz

’2’ for 440-480MHz ’3’ for 480-520MHz

-XXXX ’0’ for wide bandwidth (25kHz) ’3’ for mid bandwidth (20kHz) ’5’ for narrow bandwidth (12.5kHz)

Options

T85X-XX-XXXX The Options group uses four digits and/or letters to indicate

any options that may be fitted to the product. This includes standard options and special options for specific customers. ’0000’ indicates a standard Tait product with no options fitted. The large number of options precludes listing them here.

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M850-00

T855 General Information

B1.13

1.4 Standard Product Range

The following table lists the range of standard T855 types (i.e. no options fitted) available at the time this manual was published. Consult your nearest Tait Dealer or Customer Service Organisation for more information.

Frequency Range (MHz) 400-440

IF Bandwidth (kHz) 7.5 12 15

TCXO ±1ppm -20°C to +60°C

Receiver Type: T855- 15-0000 13-0000 10-0000

Frequency Range (MHz) 440-480

IF Bandwidth (kHz) 7.5 12 15

TCXO ±1ppm -20°C to +60°C

Receiver Type: T855- 25-0000 23-0000 20-0000

Frequency Range (MHz) 480-530

IF Bandwidth (kHz) 7.5 15

TCXO ±1ppm -20°C to +60°C

Receiver Type: T855- 35-0000 30-0000

•••

••

You can identify the receiver type by checking the product code printed on a label on the rear of the chassis (Figure 1.1 in Part A shows typical labels). You can further verify the receiver type by checking the placement of an SMD resistor in the table that is screen printed onto the PCB (refer to Section 6.1 for more details).

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B1.14

T855 General Information

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T855 Circuit Operation

2 T855 Circuit Operation

This section provides a basic description of the circuit operation of the T855 receiver.

B2.1

Note:

Refer to Section 6 where the parts lists, grid reference index and diagrams will provide detailed information on identifying and locating components and test points on the main PCB. The parts list and diagrams for the VCO PCB are in Part E.

The following topics are covered in this section.

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

Section Title Page

2.1 Introduction 2.3

2.2 Receiver Front End 2.4

2.3 Mixer 2.5

2.4 IF Circuitry 2.5

2.5 Noise Mute (Squelch) 2.6

2.6 Carrier Mute 2.6

2.7 Audio Processor 2.7

2.8 Power Supply And Regulators 2.8

2.9 Microcontroller 2.9

2.10 Synthesised Local Oscillator 2.10

2.11 VCO 2.11

2.12 Received Signal Strength Indicator (RSSI) 2.12

Figure Title Page

2.1

2.2

2.3

2.4

2.5

2.6

2.7

T855 High Level Block Diagram T855 Front End, IF and Mute Block Diagram T855 Audio Processor Block Diagram T855 Power Supply And Regulators Block Diagram T855 Microcontroller Block Diagram T855 Synthesiser Block Diagram T855 RSSI Block Diagram (T800-04-0000 RSSI PCB)

2.3

2.4

2.7

2.8

2.9

2.10

2.12

Page 42

B2.2

T855 Circuit Operation

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2.1 Introduction

T855 Circuit Operation

Noise

Mute

B2.3

Mixer Mixer Limiter

Front

End

Synthesised

Local

Oscillator

45MHz

Second

Local

Oscillator

12.8MHz Master

Oscillator

455kHz

Figure 2.1 T855 High Level Block Diagram

The T855 receiver consists of a number of distinct stages:

• front end

•mixer

• synthesised local oscillator

•IF

• audio processor

• mute (squelch)

Detector

RSSI

Audio

Processor

Carrier

Mute

Speaker

600Ω

}

Line

• regulator circuits

• received signal strength indicator (RSSI).

These stages are clearly identifiable in Figure 2.1. Refer to the circuit diagrams in Section 6 for further detail.

Page 44

B2.4

T855 Circuit Operation

M850-00

2.2 Receiver Front End

(Refer to the front end, IF section and audio processor circuit diagrams (sheets 4, 3 and 2 respectively) in Section 6.3.)

Local Oscillator

(From Synthesiser)

RF In

400-530MHz

Harmonic

Filter

Helical

Filter

Amp

Helical

Filter

4dB Pad

Diplexer

Post

Mixer

Amp

4-Pole

Crystal

Filter

Amp

2-Pole

Crystal

Filter

45MHz

Active

FilterLFAmp

Diode

Detector

Gain Adjust

Amp

2nd LO

44.545MHz

Smoothing

Mixer

(MC3361)

Filter

Mixer

Ceramic

Filter

455kHz

Link:

Comparator

Limiter

(MC3361)

RSSI

Carrier Mute Noise Mute

Mute Adjust

45MHz

Detector

(MC3361)

Buffer

Amp

Comparator

Gating

Delays

t∆

Low Pass Filter

Mute Adjust

Comparator

Buffer

Amp

Audio (To Audio Processor)

RSSI Output Voltage (To D-Range Connector)

Rx Gate Out (To Audio Processor)

Audio Section

Figure 2.2 T855 Front End, IF and Mute Block Diagram

The incoming signal from the N-type antenna socket is fed through a 9-pole, low pass filter with a cut frequency of approximately 600MHz. This low loss filter (typically less than 0.5dB over 400-530MHz) provides excellent immunity to interference from high frequency signals.

The signal is then further filtered, using a high performance helical resonator doublet (FL410) which provides exceptional image rejection, before being amplified by approximately 8dB (Q410). The signal is then passed through a further helical filter doublet (FL420) before being presented to the mixer via a 2dB attenuator pad.

Each sub-block within the front end has been designed with 50 ohm terminations for ease of testing and fault finding. The overall gain from the antenna socket to the mixer input is approximately 2dB.

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M850-00

T855 Circuit Operation

B2.5

2.3 Mixer

(Refer to the front end circuit diagram (sheet 4) in Section 6.3 and Figure 2.2.)

IC410 is a high level mixer requiring a local oscillator (LO) drive level of +17dBm (nominal). The voltage controlled oscillator (VCO) generates a level of +21dBm (typical) and this is fed to the mixer via a 5dB attenuator pad. A diplexer terminates the IF port of the mixer in a good 50 ohms, thus preventing unnecessary intermodulation distortion.

2.4 IF Circuitry

(Refer to the IF section circuit diagram (sheet 3) in Section 6.3 and Figure 2.2.)

Losses in the mixer are made up for in a tuned, common gate, post mixer amplifier (Q310). Several stages of amplification and filtering are employed in the IF circuitry. The first crystal filter is a 4-pole device (&XF300) which is matched into 50 ohms on both its input and output ports. This stage is followed by a common base amplifier (Q320) whose output is matched into a 2-pole crystal filter (&XF301). The signal is then amplified using a high gain MOSFET amplifier (Q330), after which the signal is mixed down to 455kHz with the second crystal local oscillator (44.5455MHz).

The 455kHz signal is filtered using a 6-pole ceramic filter (&XF302) before being limited and detected. Q340 provides a buffered 455kHz output for use with the optional RF level detector (RSSI)

The second IF mixer, limiter and detector is in a 16-pin IC (IC310). Quadrature detection is employed, using L390, and the recovered audio on pin 9 of IC310 is typically 1V p-p for 60% system deviation.

Page 46

B2.6

T855 Circuit Operation

M850-00

2.5 Noise Mute (Squelch)

(Refer to the audio processor and IF section circuit diagrams (sheets 2 and 3 respectively) in Section 6.3 and Figure 2.2.)

The noise mute operates on the detected noise outside the audio bandwidth. An operational amplifier in IC310 is used as an active band pass filter centred on 70kHz to filter out audio components. The noise spectrum is then further amplified in a variable gain, two-stage amplifier (Q350 & Q360) with additional filtering. The noise is then rectified (D310) and filtered to produce a DC voltage proportional to the noise amplitude. The lowest average DC voltage corresponds to a high RF signal strength and the highest DC voltage corresponds to no signal at the RF input.

The rectified noise voltage is compared with a threshold voltage set up on RV230, the front panel "Gating Sensitivity" potentiometer. Hysteresis is provided by the feedback resistor (R267) to prevent the received message from being chopped when the average noise voltage is close to the threshold. R281 and R280 determine the mute opening and closing times and, in combination with solder links SL210 and SL220, provide three time delay options (SL210 is linked as standard - refer to Section 3.8). The mute control signal at pin 7 of IC270 is used to disable the speaker and line audio outputs. The speaker output can be separately enabled for test purposes by operating the front panel mute disable switch, SW201.

2.6 Carrier Mute

(Refer to the audio processor and IF section circuit diagrams (sheets 2 and 3 respectively) in Section 6.3 and Figure 2.2.)

A high level carrier mute facility is also available. The RSSI (refer to Section 2.12) provides a DC voltage proportional to the signal strength. This voltage is compared with a preset level, set up on RV235, and may be linked into the mute timing circuit using PL250. PL250 selects either the noise mute or the carrier mute. From this point both the noise and carrier mute circuits operate in the same manner, using common circuitry.

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T855 Circuit Operation

2.7 Audio Processor

(Refer to the audio processor circuit diagram (sheet 2) in Section 6.3.)

B2.7

From

IF Stage

Demodulated

Signal

Flat/De-

emphasis

*IF

Comp

(*IF Audio

Compensation

Circuit)

PL210

2 3

LPF

Flat/De-

emphasis

Amplifier

PL220

1 3

Audio 1

Output

High Pass

Filter

Audio 2

Input

RSSI

(Optional)

Speech

PL240

1 2 3 4 5

1 2 3

PL230

Carrier

Mute

Noise

Mute

Monitor Volume

Line

Level

PL250

3 2 1

PL260

Speaker Mute

Line Mute

PL270

1 2

Driver Amp

12V

Relay

Rx Disable

Timer

Driver Amp

Figure 2.3 T855 Audio Processor Block Diagram

The recovered audio on pin 9 of IC310 is passed through a compensation network and processed in a third order elliptic active filter to give the required response. Linking (PL220 & PL210) is available to give either a flat or de-emphasised audio response, with de-emphasis giving a -6dB/octave roll off. The output of IC210 is split to provide separate paths for the speaker and line outputs. The "Audio 1", Audio 2" and "Speech" lines allow access to the receiver’s audio path for external signalling purposes (refer to Section 3.5).

RSSI Output

Mute Relay

Gate Output

Rx Disable (Optional Pad)

Mute Disable

Speaker Output

Line Output

Line Monitor

The signals are passed to audio drive amplifiers IC240 and IC260. Under muted conditions the inputs of these amplifiers are shunted to ground via transistors Q230 and Q290 respectively. The audio output of IC240 has a DC component which is removed by C249, and this then drives a speaker directly. The output of IC260 is fed into a line transformer to provide a balanced 2-wire or 4-wire, 600 ohm output.

The speaker volume is set using the front panel "Monitor Volume" knob (RV205) and the line level is set using the recessed "Line Level" potentiometer (RV210).

The red front panel "Gate" LED (D250) indicates the status of the mute circuit. When a signal above the mute threshold is received, the LED is illuminated. The "Monitor Mute" switch (SW201) on the front panel opens the mute, allowing continuous monitoring of the audio signal (on = audio muted; off = audio unmuted).

The mute control line is available on pad 234 ("RX GATE OUT") for control of external circuitry. A high (9V) on pad 234 indicates that the audio is disabled and a low (0V) indicates that a signal above the mute threshold level is being received.

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B2.8

T855 Circuit Operation

M850-00

The audio can also be disabled using the "RX-DISABLE" inputs, pads 225 or 228, having connected the "RX-DISABLE" link between pins 1 & 2 of PL260. An adjustable time delay (RV220) is provided on these lines. In order to disable the audio, either pad must be pulled to 0V (refer to Section 1.4 in Part G).

An undedicated relay is provided (RL210) for transmitter keying or other functions and this can be operated from the mute line by linking PL270.

2.8 Power Supply And Regulators

(Refer to the regulators circuit diagram (sheet 6) in Section 6.3.)

13.8V Nom. From Rear D-Range 1

Reg

Amp

Switching

5V Dig

Reg

LVI

µP

Reset

13.8V Nom.

5V 5V Dig9V 20V

Figure 2.4 T855 Power Supply And Regulators Block Diagram

The T855 is designed to operate off a 10.8-16V DC supply (13.8V nominal). A 5.3V regulator (IC630) runs directly from the 13.8V rail, driving much of the synthesiser circuitry. It is also used as the reference for a DC amplifier (IC640, Q630 & Q620) which provides a medium current capability 9V supply.

A switching power supply, based on Q670 and Q660, runs off the 9V supply and provides a low current capability +20V supply. This is used to drive the synthesiser loop filter (IC740), giving a VCO control voltage of up to 20V.

The 13.8V supply drives both output audio amplifiers without additional regulation. A separate 5V regulator (IC610) drives the microprocessor and associated digital circuitry. The output of this regulator is monitored by the Low Voltage Interrupt (LVI) circuit (IC650).

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T855 Circuit Operation

2.9 Microcontroller

(Refer to the microcontroller circuit diagram (sheet 8) in Section 6.3.)

B2.9

Watchdog Timer

& LVI

Watchdog

EEPROM

Microcontroller Cavity

Channel

Select

Port

Auxiliary

Output

Port

Synthesiser

12.8MHz Clock

External

Serial

Port

Audio In

Speech

5V Digital

Regulator

5V Reset

Microcontroller

Converter

CTCSS Decoder

Figure 2.5 T855 Microcontroller Block Diagram

Overall system control of the T855 is accomplished by the use of a member of the 80C51 family of microcontrollers (IC810) which runs from internal ROM and RAM. Four ports are available for input/output functions.

Non-volatile data storage is achieved by serial communication with a 16kBit EEPROM (IC820). This serial bus is also used by the microcontroller to program the synthesiser (IC740).

The main tasks of the microcontroller are as follows:

• program the synthesiser;

• interface with the PGM800Win programming software at 9600 baud via the

serial communication lines on D-range 1 (PL100) & D-range 2;

• monitor channel change inputs from D-range 2;

• generate timing waveforms for CTCSS detection;

• coordinate and implement timing control of the receiver.

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T855 Circuit Operation

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2.10 Synthesised Local Oscillator

(Refer to the synthesiser circuit diagram (sheet 7) in Section 6.3 and the VCO circuit diagram in Part E.)

12.8MHz

Reference

Oscillator

Serial

Bus

FREQUENCY SYNTHESISER IC

Reference

Divider

ref

Clk Data En

Controller

Phase

Detector

Charge

Pump

Programmable

Divider

Loop Filter

Prescaler

64/65

VCO Buffer

Buffer

VCO PCB

Output

Buffer

+22dBm

L.O.

Figure 2.6 T855 Synthesiser Block Diagram

The synthesiser (IC740) employs a phase-locked loop (PLL) to lock a voltage controlled oscillator (VCO) to a given reference frequency. The synthesiser receives the divider information from the control microprocessor via a 3-wire serial bus (clock, data, enable). When the data has been latched in, the synthesiser processes the incoming signals from the VCO buffer (f

) and the reference oscillator (f

ref

A reference oscillator at 12.8MHz (IC700) is buffered (IC710) and divided down to

6.25kHz or 5kHz within the synthesiser IC (IC740).

A buffered output of the VCO is divided with a prescaler and programmable divider which is incorporated into the synthesiser chip (IC740). This signal is compared with the reference signal at the phase detector (also part of the synthesiser chip). The phase detector outputs drive a balanced charge pump circuit (Q760, Q770, Q775, Q780, Q785) and active loop filter (IC750, Q790) which produces a DC voltage between 0V and 20V to tune the VCO. This VCO control line is further filtered to attenuate noise and other spurious signals. Note that the VCO frequency increases with increasing control voltage.

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T855 Circuit Operation

B2.11

2.11 VCO

(Refer to the VCO circuit diagram in Part E.)

The VCO transistor (Q1) operates in a common emitter, and uses a transmission line resonator (TL1). The transmission line is used in a two port configuration with varicaps positioned at one end. The VCO control voltage from the loop filter (IC750) is applied to the varicaps (D1 & D2) to facilitate tuning. The VCO output is coupled into a cascode amplifier stage (Q2 & Q3) which supplies +10dBm (nominal) output. Further amplification in Q5 brings the output drive level to +20dBm to drive the mixer.

A low level "sniff" is taken from the input to Q5 to drive the divider buffer to the synthesiser (IC740).

The VCO operates at the actual frequency required by the first mixer, i.e. there are no multiplier stages.

The VCO frequency spans from either 355-395MHz, 395-435MHz or 435-485MHz according to product type (refer to Section 1.4). The VCO is tuned to 45MHz below the desired receive frequency (low side injection) to produce a 45MHz IF signal at the output of the mixer.

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B2.12

T855 Circuit Operation

M850-00

2.12 Received Signal Strength Indicator (RSSI)

(Refer to the T800-04-0000 RSSI PCB circuit diagram in Section 6.2 and the IF section circuit diagram (sheet 3) in Section 6.3.)

The RSSI option PCB plugs directly into the main PCB (support circuitry being fitted as standard). It is fitted to the T855 whenever receiver signal strength monitoring is required, e.g. trunking or voting. Its function is to provide a DC voltage proportional to the signal level at the receiver input. The DC voltage is available at D-range 1 (PL100 pin 5).

The RSSI also provides the capability for high level signal strength muting, which may be selected on PL250 (refer to Section 3.5). The mute threshold may be set between

-115dBm and -70dBm by RV235.

Amp Detector Error Amp

RSSI Input

Temp Comp Q1D

Q1C Q1A &

Variable Gain Stage Q1E

Temp Comp

DC Amp (Gain= x33)

Q1B

VDC

RSSI Output 1V/10dB

NTC

DC Offset

(Ref)

Figure 2.7 T855 RSSI Block Diagram (T800-04-0000 RSSI PCB)

The variable gain stage (Q1A) is a common emitter amplifier with its emitter grounded and the AGC control loop voltage applied to its base. Since the AGC loop will maintain a constant signal level at the collector, the gain of Q1 must be proportional to the incoming 455kHz signal level. The gain of Q1 is linearly proportional to its collector current which itself is exponentially related to the base-emitter voltage. Thus there is a logarithmic relationship between the base-emitter voltage and the gain. The circuit therefore produces a feedback voltage, and an output voltage, logarithmically related to the RF input signal.

The AGC loop is followed by a DC amplifier which provides level shifting, temperature compensation and gain to give a nominal 1V/10dB at the RSSI output. RV320 on the main PCB is used to set the RSSI voltage to a fixed value at a given RF input signal strength.

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T855 Initial Tuning & Adjustment

3 T855 Initial Tuning & Adjustment

B3.1

Caution:

The following section describes both short and full tuning and adjustment procedures and provides information on:

• channel programming

• selecting the required audio links

• synthesiser alignment

• receiver front end and IF alignment

• noise and carrier level mute adjustment

• setting the line and monitor output levels

• setting up the RSSI.

Note:

Refer to Figure 4.3 which shows the location of the main tuning and adjustment controls. Refer also to Section 6 where the parts lists, grid reference index and diagrams will provide detailed information on identifying and locating components and test points on the main PCB. The parts list and diagrams for the VCO PCB are in Part E.

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

Section Title Page

3.1 Introduction 3.3

3.2 Channel Programming 3.3

3.3 Test Equipment Required 3.4

3.4

3.4.1

3.4.2

3.4.3

3.4.4

3.4.4.1

3.4.4.2

3.4.5

3.4.6

3.4.6.1

3.4.6.2

3.4.6.3

3.4.7

Short Tuning Procedure

Introduction Synthesiser Alignment Front End Alignment Mute Adjustment

Noise Mute Carrier Level Mute

Line Amplifier Output CTCSS

Decoder Operation Opening Sinad High Pass Filter

RSSI (If Fitted)

3.5

3.6

3.7

3.8

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B3.2

T855 Initial Tuning & Adjustment

Section Title Page

M850-00

3.5

3.5.1

3.5.2

3.6 Synthesiser Alignment 3.10

3.7 Alignment Of Receiver Front End And IF 3.10

3.8 Gating Delay 3.12

3.9 Noise Mute Adjustment 3.12

3.10 Carrier Level Mute 3.12

3.11

3.11.1

3.11.2

3.12

3.12.1

3.12.2

3.12.3

Audio Processor Links

General Audio Processor Linking Details For CTCSS

Audio Processor

Line Amplifier Output Monitor Amplifier Output (Speaker Output)

CTCSS

Decoder Operation Opening Sinad High Pass Filter

3.8

3.9

3.13

3.14

3.13 RSSI 3.14

Figure Title Page

3.1

3.2

T855 Test Equipment Set-up For Short Tuning Procedure T855 Test Equipment Set-up For Full Tuning & Adjustment

Procedure

3.4

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3.1 Introduction

T855 Initial Tuning & Adjustment

B3.3

When you receive your T855 receiver it will be run up and working on a particular frequency (the "default channel") 5MHz switching range (i.e. ±2.5MHz from the factory programmed frequency), you should only need to reprogram the receiver with the PGM800Win software (refer to the PGM800Win programming kit and Section 3.2 below).

However, if you want to switch to a frequency outside the 5MHz switching range, you will have to reprogram and re-tune the receiver to ensure correct operation. In this case you should carry out the short tuning procedure described in Section 3.4.

If you have carried out repairs or other major adjustments, you must carry out the full tuning and adjustment procedure described in this section (except for Section 3.4).

. If you want to switch to a frequency that is within the

3.2 Channel Programming

You can program up to 128 channel frequencies into the receiver’s EEPROM memory (IC820) by using the PGM800Win software package and an IBM PGM800Win to select the receiver’s current operating frequency (or "default channel").

If the receiver is installed in a rack frame, you can program it via the programming port in the speaker panel. However, you can also program the receiver before it is installed in a rack frame as follows:

 PC. You can also use

• by using a T800-01-0010 calibration test unit;

• via D-range 1;

• via D-range 2 (standard T800-03-0000 auxiliary D-range only);

• via SK805 (internal Micromatch connector).

If you do not use the T800-01-0010, you will have to connect the PC to the receiver via a module programming interface (such as the T800-01-0004).

For a full description of the channel programming procedure, refer to the PGM800Win programming software user’s manual.

Note:

When an auxiliary D-range kit (D-range 2 - T800-03-0000) is fitted, you can also select a channel with an external switch, such as the DIP switch on the rack frame backplane PCB. Refer to Part C in the T800 Series Ancillary Equipment Service Manual (M800-00-101 or later issue) or consult your nearest Tait Dealer or Customer Service Organisation for further details.

1. Use the "Read Module" function in PGM800Win to find out what the default channel is.

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B3.4

T855 Initial Tuning & Adjustment

3.3 Test Equipment Required

You will need the following test equipment:

• computer with PGM800Win installed

• T800 programming kit

• module programming interface (e.g. T800-01-0004 - optional)

• 13.8V power supply

• digital multimeter

• audio signal generator

M850-00

• RF signal generator or RF test set (optional)

• audio voltmeter

• sinad meter

• oscilloscope

not needed for short tuning procedure

• distortion meter

• T800-01-0010 calibration test unit (optional)

•4Ω speaker (not needed if the calibration test unit is used)

Figure 3.1 and Figure 3.2 show typical test equipment set-ups (with and without a T800-01-0010 calibration test unit).

RF Signal

Generator

Audio Signal

Generator

PGM800Win

PSU

External Modulation

+13.8V

-Ve

RF In

Receiver

T800

Calibration

Test Unit

Line Line

Sinad Meter

Audio

Voltmeter

Figure 3.1 T855 Test Equipment Set-up For Short Tuning Procedure

PSU

RF Signal

Generator

External Modulation

Audio Signal

Generator

PGM800Win

+13.8V

-Ve

RF In

Receiver

GND

via module programming interface

Serial

(e.g. T800-01-0004)

Com

Line Line

Speaker Output

600Ω

Distortion

Meter

Sinad Meter

Audio

Voltmeter

Oscilloscope

CH1

GND

(Or 4Ω Resistor)

CH2

Probe

4Ω Speaker

Figure 3.2 T855 Test Equipment Set-up For Full Tuning & Adjustment Procedure

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T855 Initial Tuning & Adjustment

B3.5

3.4 Short Tuning Procedure

Use this procedure only if you want to reprogram the receiver to a frequency outside the 5MHz switching range and do not intend to carry out any other major adjustments or repairs.

3.4.1 Introduction

Reprogram the operating frequency as described in the PGM800Win programming kit (refer to Section 3.2).

Remove the top cover (nearest the handle).

Set up the test equipment as described in Section 3.3.

Set the links in the audio processor section as required (refer to Section 3.5).

3.4.2 Synthesiser Alignment

• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-

ures the synthesiser loop voltage).

• Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V.

Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V on the middle channel. If there is no middle channel, tune C6 so that the channels

are symmetrically placed around a loop voltage of 10V. All channels should lie within the upper and lower limits

of 16V and 3V respectively. Do not attempt to program channels with a greater fre-

quency separation than the specified switching range of 5MHz.

3.4.3 Front End Alignment

Note 1:

Note 2:

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

For multichannel operation align the receiver on a frequency in the middle of the required band.

Inject a strong on-channel RF signal with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz into the antenna socket and adjust the helical resonators #FL410 & #FL420 to give best sinad.

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B3.6

T855 Initial Tuning & Adjustment

Continually decrease the RF level to maintain 12dB sinad.

Readjust FL410 and FL420 to give best sinad.

With PL210 and PL220 connected for de-emphasised audio response, the receiver sensitivity should be better than -117dBm, assuming that the audio levels are not being overdriven (refer to Section 3.4.5).

3.4.4 Mute Adjustment

3.4.4.1 Noise Mute

Connect pins 1 & 2 of PL250 to enable the noise mute.

Set the RF level to -105dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Set RV230 (front panel gating sensitivity) fully anticlockwise.

M850-00

Adjust RV310 (noise mute gain) to close the mute (if necessary turn off the RF signal and then turn it on again).

Rotate RV310 anticlockwise until the mute just opens.

Adjust RV230 for the required opening sinad.

3.4.4.2 Carrier Level Mute

Connect pins 2 & 3 of PL250 to enable the carrier mute and disable the noise mute.

Apply an on-channel signal from the RF generator at the required mute opening level with ±3kHz deviation (±2.4kHz) [±1.5kHz] at ±1kHz.

Adjust RV235 (carrier mute) to close the mute (if necessary, momentarily turn off the RF), then slowly adjust it until the mute just opens. The mute should now open at this preset level.

3.4.5 Line Amplifier Output

Apply an on-channel signal from the RF generator at a level of -70dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust RV210 (front panel line level) to set the line level to the required output level.

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3.4.6 CTCSS

3.4.6.1 Decoder Operation

Program a CTCSS tone on the set channel using PGM800Win.

Set the RF signal generator output to -70dBm.

Modulate the generator with:

• a 1kHz tone at ±3kHz deviation (±2.4kHz) [±1.5kHz]

• a CTCSS tone at the programmed frequency at ±500Hz deviation (±400Hz) [±300Hz].

Check that the receiver gate opens and the front panel "Gate" LED is on.

3.4.6.2 Opening Sinad

B3.7

Adjust RV230 (front panel gating sensitivity) fully clockwise.

Reduce the RF signal level to -110dBm.

Observe the sinad meter and reduce the RF level until the receiver mute closes.

Slowly increase the signal level until the receiver mute just opens and stays open.

With PL240 pins 1 & 2 linked (G - H; high pass filter bypassed), check that the sinad is less than 6dB.

Reset RV230.

3.4.6.3 High Pass Filter

Set the audio processor links as follows:

Plug Link Function

PL210 1 - 2 A - B de-emphasised response

PL230 2 - 3 N - P audio from internal CTCSS speech filter

PL240 4 - 5 K - L audio input via PL230 or I/O pad

Reset the RF signal generator output to -70dBm and note the line level (measurement A).

Reduce the 1kHz generator to zero output and measure the line level again (measurement B).

Check that measurement B is at least 30dB below measurement A.

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T855 Initial Tuning & Adjustment

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3.4.7 RSSI (If Fitted)

The T800-04-0000 RSSI is an optional PCB which adds signal strength monitoring and high level mute facilities to the basic receiver.

Ensure the T800-04-0000 PCB is fitted in SK320 and SK330 in the IF compartment.

Apply an on-channel signal from the RF generator at a level of -100dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust RV320 (RSSI level) to give 2.0V RSSI output on pin 5 of D-range 1 (PL100) when measured with a high impedance DMM.

3.5 Audio Processor Links

3.5.1 General

Use the following table to set up the audio processor to the configuration you require. You should set the audio processor links before carrying out the receiver alignment. The factory settings are shown in brackets [ ].

Plug Link

PL210

PL220

PL230*

PL240

PL250

[1 - 2]

2 - 3

1 - 2

[2 - 3]

1 - 2

[2 - 3]

3 - 4

1 - 2

[2 - 3]

3 - 4 4 - 5

[1 - 2]

2 - 3

[A - B]

B - C

D - E

[E - F]

M - N

[N - P]

P - Q

G - H

[H - J]

J - K

K - L

[R - S]

S - T

Function

de-emphasised response flat response

flat response de-emphasised response

audio input via AUDIO-2 pad audio from internal CTCSS speech filter audio input via I/O pad P250

bypass high pass filter

300Hz high pass filter in circuit

audio input via PL230 or I/O pad

noise mute carrier mute

PL260

PL270

a. The letters in this column and in the table in Section 3.5.2 below refer to the identification

letters screen printed onto the PCB beside each set of pins.

b. Refer to Section 3.5.2 for further details.

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1 - 2

[2 - 3]

[1 - 2]

2 - 3

U - V

[V - W]

[X - Y]

Y - Z

RX-DISABLE link not connected

relay link not connected

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T855 Initial Tuning & Adjustment

B3.9

3.5.2 Audio Processor Linking Details For CTCSS

You must connect the audio processor links correctly according to the CTCSS option used, as shown in the table below.

CTCSS Option PL230 PL240

standard, no CTCSS 2 - 3 N - P 2 - 3 H - J

received CTCSS + speech passed to line output

high pass filtered speech, internal CTCSS detection

external CTCSS detection 1 - 2 M - N 4 - 5 K - L

The conditions stated in the above table are defined as follows:

• standard, no CTCSS - no CTCSS or other sub-audio signalling used

- audio bandwidth 300Hz to 3kHz

- hum & noise -55dB

• received CTCSS tone - tone and speech transmitted down 600 ohm line + speech to line output - audio bandwidth 10Hz to 3kHz

- hum & noise -45dB

• high pass filtered speech - 400Hz to 3kHz + internal CTCSS detection - hum & noise -30dB with 250.3Hz tone present

• external CTCSS detection - decoding performed through the receiver (but

externally)

- speech injected back into receiver via "AUDIO-2" and sent down 600 ohm line

3 - 4 P - Q 1 - 2 G - H

2 - 3 N - P 4 - 5 K - L

Note 1:

Note 2:

AUDIO-2 is available on D-range 1 (PL100) pin 7 via the link resistor R160. Although PL100 pin 7 is already assigned to SERIAL-COM, this can be disabled by removing R808.

External CTCSS units can connect in series with the audio chain via AUDIO-1 and AUDIO-2.

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T855 Initial Tuning & Adjustment

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3.6 Synthesiser Alignment

• Ensure that the receiver has been programmed with the required frequencies using the PGM800Win software.

• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this measures the synthesiser loop voltage).

• Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V.

Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of

10V on the middle channel. If there is no middle channel, tune C6 so that the channels

are symmetrically placed around a loop voltage of 10V. All channels should lie within the upper and lower limits

of 16V and 3V respectively. Do not attempt to programme channels with a greater fre-

quency separation than the specified switching range of 5MHz.

• The TCXO =(IC700) output frequency should be trimmed when the IF is tuned refer to Section 3.7.

3.7 Alignment Of Receiver Front End And IF

Note:

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

Align the synthesiser as instructed in Section 3.6. For multichannel operation align the receiver on a frequency in the middle of the required band.

Inject a strong on-channel RF signal with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz into the antenna socket and adjust the helicals (#FL410 and #FL420) to give the best sinad.

Continually decrease the RF level to maintain 12dB sinad.

Roughly tune IF coils L310, L320, L330, L340, L350, L360, L370, L380, L385 and L390 for best sinad.

While maintaining a low level unmodulated RF input to the receiver, loosely couple into the first IF an additional high level signal at 45MHz - you will hear a beat note.

Trim the synthesiser TCXO (=IC710) for zero beat.

While maintaining the low level RF input to the receiver, loosely couple into the second IF an additional high level signal at 455kHz - you will hear a beat note.

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Tune L385 for zero beat.

T855 Initial Tuning & Adjustment

B3.11

Note:

If a second oscillator is not available, you can connect a frequency counter to IC710 pin 8 (i.e. after the TCXO buffer) via an oscilloscope probe to measure the TCXO frequency directly (12.8MHz). At this point the voltage level is approximately 4V p-p.

Readjust the front end helicals (#FL410 and #FL420) to give the best sinad.

Change the RF signal level to -75dBm and modulate with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Connect an oscilloscope probe to SK320 pin 3 (RSSI 455kHz input) and connect plugs PL210 and PL220 to give a flat audio response (refer to Section 3.5).

Readjust L310, L320, L330, L340, L350, L360, L370 and L380 to give a maximum amplitude response on the oscilloscope with minimal amplitude modulation.

If you would like a more accurate method of tuning the IF, refer to the sweep tuning method described in Section 5.5.5.

Further adjust these coils, along with L390, for minimum audio distortion, ensuring that the 455kHz level (on the oscilloscope) does not fall significantly.

Check that the distortion reading is:

wide bandwidth ≤2% mid and narrow bandwidth ≤4%.

If required, reconnect plugs PL210 and PL220 to give a de-emphasised audio response and check that the distortion reading is ≤2% (all bandwidths).

Reduce the RF level until 12dB sinad is reached. The receiver sensitivity should be better than -117dBm (de-emphasised) or -111dBm (flat), assuming that the audio levels are not being overdriven (refer to Section 3.11).

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B3.12

T855 Initial Tuning & Adjustment

M850-00

3.8 Gating Delay

Two solder links (SL210 & SL220) are provided on the bottom of the PCB to allow three gate delay time options, as shown in the table below.

SL210 SL220 Closing Delay

linked not linked <50ms*

not linked linked <25ms

not linked not linked <20ms

*Factory setting.

3.9 Noise Mute Adjustment

Connect pins 1 & 2 of PL250 to enable the noise mute.

Align the receiver as instructed in Section 3.6 and Section 3.7.

Set the RF level to -105dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Set RV230 (front panel gating sensitivity) fully anticlockwise.

Adjust RV310 (noise mute gain) to close the mute (if necessary turn off the RF signal and then turn it on again).

Rotate RV310 anticlockwise until the mute just opens.

Once the mute has been set up as described above, adjust RV230 for the required opening sinad.

3.10 Carrier Level Mute

Connect pins 2 & 3 of PL250 to enable the carrier mute and disable the noise mute.

Apply an on-channel signal from the RF generator at the required mute opening level with ±3kHz deviation (±2.4kHz) [±1.5kHz] at ±1kHz.

Adjust RV235 (carrier mute) to close the mute (if necessary, momentarily turn off the RF), then slowly adjust it until the mute just opens. The mute should now open at this preset level.

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T855 Initial Tuning & Adjustment

3.11 Audio Processor

3.11.1 Line Amplifier Output

Apply an on-channel signal from the RF generator at a level of -70dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust RV210 (front panel line level) to give an output of +10dBm on the 600 ohm line.

Check for any clipping or distortion on the oscilloscope.

Set the line level to the required output level.

3.11.2 Monitor Amplifier Output (Speaker Output)

B3.13

Adjust RV205 (front panel monitor volume) to give an output of 2V rms into a 4 ohm resistive load.

Check for any clipping or distortion on the oscilloscope.

Switch to a 4 ohm speaker and adjust RV205 to the required level.

3.12 CTCSS

3.12.1 Decoder Operation

Program a CTCSS tone on the set channel using PGM800Win.

Set the RF signal generator output to -70dBm.

Modulate the generator with:

• a 1kHz tone at ±3kHz deviation (±2.4kHz) [±1.5kHz]

• a CTCSS tone at the programmed frequency at ±500Hz deviation (±400Hz) [±300Hz].

Check that the receiver gate opens and the front panel "Gate" LED is on.

3.12.2 Opening Sinad

Adjust RV230 (front panel gating sensitivity) fully clockwise.

Reduce the RF signal level to -110dBm.

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B3.14

T855 Initial Tuning & Adjustment

Observe the sinad meter and reduce the RF level until the receiver mute closes.

Slowly increase the signal level until the receiver mute just opens and stays open.

With PL240 pins 1 & 2 linked (G - H; high pass filter bypassed), check that the sinad is less than 6dB.

Reset RV230.

3.12.3 High Pass Filter

Set the audio processor links as follows:

Plug Link Function

PL210 1 - 2 A - B de-emphasised response

PL230 2 - 3 N - P audio from internal CTCSS speech filter

M850-00

PL240 4 - 5 K - L audio input via PL230 or I/O pad

Reset the RF signal generator output to -70dBm and note the line level (measurement A).

Reduce the 1kHz generator to zero output and measure the line level again (measurement B).

Check that measurement B is at least 30dB below measurement A.

3.13 RSSI

The T800-04-0000 RSSI is an optional PCB which adds signal strength monitoring and high level mute facilities to the basic receiver.

Ensure the T800-04-0000 PCB is fitted in SK320 and SK330 in the IF compartment.

Align the receiver as instructed in Section 3.6 and Section 3.7.

Apply an on-channel signal from the RF generator at a level of -100dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust RV320 (RSSI level) to give 2.0V RSSI output on pin 5 of D-range 1 (PL100) when measured with a high impedance DMM.

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T855 Functional Testing

4 T855 Functional Testing

B4.1

Caution:

The following test procedures will confirm that the T855 has been tuned and adjusted correctly and is fully operational.

Note 1:

Note 2:

Refer to Figure 4.3 for the location of the main tuning and adjustment controls, and to Section 3.3 for the test equipment set-up. Refer also to Section 6 where the parts lists, grid reference index and diagrams will provide detailed information on identifying and locating components and test points on the main PCB. The parts list and diagrams for the VCO PCB are in Part E.

The following topics are covered in this section.

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

Section Title Page

4.1 Current Consumption 4.3

4.2 Sensitivity 4.3

4.3 Switching Range 4.3

4.4 Audio Distortion 4.4

4.5 Ultimate Signal-To-Noise Ratio 4.4

4.6 De-emphasised Audio Frequency Response 4.5

4.7 Noise Mute (If Linked In) 4.6

4.8 RSSI (If Fitted) 4.6

4.9 Carrier Level Mute (RSSI Fitted & Carrier Mute Linked In) 4.7

Figure Title Page

4.1

4.2

T855 De-emphasised Audio Frequency Response T855 RSSI Voltage vs Signal Strength

4.5

4.6

4.3

T855 Main Tuning & Adjustment Controls

4.9

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B4.2

T855 Functional Testing

M850-00

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Page 69

M850-00

T855 Functional Testing

4.1 Current Consumption

Connect the T855 to a 13.8V power supply.

Rotate RV230 (front panel gating sensitivity) anticlockwise until the "Gate" LED is extinguished.

B4.3

Set switch SW201 (front panel monitor mute) to the

Check that the current in the 13.8V power cable is less than 350mA.

Rotate the RV230 clockwise until the "Gate" LED is lit.

Rotate RV210 (front panel line level) and RV205 (front panel monitor volume) to give maximum outputs.

Check that the current is less than 750mA.

Reset the front panel controls to the required settings.

position.

4.2 Sensitivity

If CTCSS is enabled, disable the CTCSS tone by either programming the T855 for "No Tone" on the set channel, or by pulling pin 10 of D-range 2 (CTCSS ENABLE) low.

Apply an on-channel signal from the RF generator with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust the RF level to give 12dB audio sinad.

Check that the sensitivity is -117dBm or better.

4.3 Switching Range

Apply an on-channel signal from the RF generator at various frequencies within the 5MHz switching range (front end bandwidth), corresponding to pre-programmed channels.

Measure the sensitivity at each frequency as described in Section 4.2.

Ensure that the sensitivity is -115dBm or better across the whole switching range.

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B4.4

T855 Functional Testing

M850-00

4.4 Audio Distortion

The level of distortion measured at the line output (refer to Figure 1.3 in Part F) gives an indication of the accuracy of the IF alignment.

Apply an accurate on-channel signal from the RF generator at a level of -70dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Adjust RV210 (front panel line level) to give +10dBm into 600 ohms.

Check that the distortion is approximately 1% THD.

Note:

For a flat response, the distortion should always be better than 2% for wide bandwidth sets or 4% for mid and narrow bandwidth sets.

Adjust RV205 (front panel monitor volume) to give 2V rms into a 4 ohm resistive load.

Check that the distortion at the monitor output is better than 2% THD.

Reset the controls before proceeding to the next set of tests.

4.5 Ultimate Signal-To-Noise Ratio

Apply a signal from the RF generator at a level of -57dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Select de-emphasis on the links provided in the audio processor (refer to Section

3.5), and link pins 2 & 3 of PL240 to include the 300Hz filter.

Adjust RV210 (front panel line level) to provide +10dBm output.

Switch off the modulation, checking that the residual noise is lower than -45dBm (-43dBm) [-39dBm] at the line output (this corresponds to S/N of 55dB (53dB) [49dB] and is in accordance with EIA measurement conditions).

Note:

31/09/98 Copyright TEL

You can make the measurement without the 300Hz high pass filter, but the result will be 10dB worse.

Page 71

M850-00

T855 Functional Testing

4.6 De-emphasised Audio Frequency Response

Set RV210 (front panel line level) to provide 0dBm output at 1kHz modulating frequency.

Sweep the modulating frequency, checking that the line audio response closely follows that shown in Figure 4.1 - the limits should not be exceeded.

B4.5

Wide Bandwidth

Mid Bandwidth

25°C 13.8V

+25

Ref. audio power: +0.0dBm @ 1kHz

+20 +15 +10

+5 +0

-5

-10

-15

-20

-25

-30

-35

Audio Level (dB ref. to O/P @ 1kHz)

-40

-45

-50

-55

100 200 300 500 1k 2k 3k 5k 10k

25°C 13.8V

+25

Ref. audio power:

-2.5dBm @ 1kHz

+20 +15 +10

+5 +0

-5

-10

-15

-20

-25

-30

-35

Audio Level (dB ref. to O/P @ 1kHz)

-40

-45

-50

-55

100 200 300 500 1k 2k 3k 5k 10k

Frequency (Hz)

Narrow Bandwidth

25°C 13.8V

+25

Ref. audio power:

-2.2dBm @ 1kHz

+20 +15 +10

+5 +0

-5

-10

-15

-20

-25

-30

-35

Audio Level (dB ref. to O/P @ 1kHz)

-40

-45

-50

-55

100 200 300 500 1k 2k 3k 5k 10k

Frequency (Hz)

Figure 4.1 T855 De-emphasised Audio Frequency Response

Page 72

B4.6

T855 Functional Testing

4.7 Noise Mute (If Linked In)

Rotate RV230 (front panel gating sensitivity) fully anticlockwise.

Apply an on-channel signal from the RF generator at a level of -110dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Increase the RF level in 1dB steps, checking that the mute opens for an RF input level of approximately -105dBm.

Turn the RF off and check that the mute closes.

Rotate RV230 clockwise and check that the mute opens.

Reset RV230 to give the required opening sinad.

M850-00

Caution:

Some RF generators can cause a false opening of the mute because the generator produces a burst of noise when the attenuation range changes. To correct the problem you will have to change generators.

4.8 RSSI (If Fitted)

Apply an on-channel signal from the RF generator at a level of -110dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Using a high impedance DMM, check that the RSSI output voltage on pin 5 of D-range 1 (PL100) is 2V (nominal).

Vary the RF level in 5dB steps and check that the RSSI output voltage changes at a rate of approximately 10dB/V over the range of -115dBm to -70dBm (refer to Figure 4.2 for RSSI voltage vs signal strength).

RSSI Voltage

-130 -120 -110 -100 -90 -80 -70 -60 RF Level (dBm)

Figure 4.2 T855 RSSI Voltage vs Signal Strength

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M850-00

T855 Functional Testing

4.9 Carrier Level Mute (RSSI Fitted & Carrier Mute Linked In)

Apply an on-channel signal from the RF generator at a level of -120dBm with ±3kHz deviation (±2.4kHz) [±1.5kHz] at 1kHz.

Increase the RF level in 2dB steps and check that the mute opens at an RF level which corresponds with the preset level on RV235 (carrier mute), i.e. between

-115dBm and -70dBm.

B4.7

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B4.8

T855 Functional Testing

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Page 75

M850-00

5 T855 Fault Finding

T855 Fault Finding

B5.1

Caution:

The following test procedures and fault finding flow charts may be used to help locate a hardware problem, however they are by no means a complete fault finding procedure. If you still cannot trace the fault after progressing through them in a logical manner, contact your nearest Tait Dealer or Customer Service Organisation. If necessary, you can get additional technical help from Customer Support, Radio Systems Division, Tait Electronics Ltd, Christchurch, New Zealand (full contact details are on page 2).

Note 1:

Note 2:

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ].

Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 2.00 and later of the software.

The following topics are covered in this section.

Section Title Page

5.1 Visual Checks 5.3

5.2 Component Checks 5.3

5.3 Front Panel LED Indicator 5.3

5.4

5.4.1

5.4.2

5.4.3

5.5

5.5.1

5.5.2

5.5.3

5.5.3.1

5.5.3.2

DC Checks

Power Rails VCO Locking Mute Operation

RF Checks

VCO Frequency RF Sensitivity Oscillator Stability

TCXO Second IF

5.4

5.5

5.6

5.5.4

5.5.5

Demodulator Output IF Distortion

5.6

Page 76

B5.2

T855 Fault Finding

Section Title Page

5.6 PGM800Win Generated Errors 5.8

M850-00

5.7

5.7.1

5.7.1.1

5.7.1.2

5.7.1.3

5.7.2

5.7.3

5.7.4

5.7.5

5.7.6

5.7.7

Fault Finding Charts

Microcontroller (IC810)

Basic Checks Serial Communication

CTCSS Decode Regulator Synthesiser Noise Mute Carrier Mute Receiver Audio

Figure Title Page

5.1

5.2

5.3

RF Test Cable IF Swept Response Ceramic Filter Swept Response

5.9

5.10

5.11

5.12

5.13

5.16

5.17

5.18

5.19

5.5

5.7

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Page 77

M850-00

T855 Fault Finding

B5.3

5.1 Visual Checks

Remove the covers from the T855 and inspect the PCB for damaged or broken components, paying particular attention to the surface mounted devices (SMDs).

Check for defective solder joints. If repair or replacement of components is considered necessary, refer to Section 3 of Part A.

5.2 Component Checks

If you suspect a transistor is faulty, you can assess its performance by measuring the forward and reverse resistance of the junctions. Unless the device is completely desoldered, first make sure that the transistor is not shunted by some circuit resistance. Use a good quality EVM (e.g. Fluke 75) for taking the measurements (or a 20k ohm/V or better multimeter, using only the medium or low resistance ranges).

The collector current drawn by multi-junction transistors is a further guide to their performance.

If an IC is suspect, the most reliable check is to measure the DC operating voltages. Due to the catastrophic nature of most IC failures, the pin voltages will usually be markedly different from the recommended values in the presence of a fault. The recommended values can be obtained from either the circuit diagram or the component data catalogue.

5.3 Front Pa nel LED Indica tor

The green "Supply" LED on the receiver front panel will flash according to the conditions described in the following table:

Flash Rate Condition

fast ( sec. on/ sec. off

approx.)

slow (1 sec. on/1 sec. off

approx.)

receiver is linked with

PGM800Win

VCO is out of lock -

refer to Section 5.4.2

unequal ( sec. on/1 sec. off

approx.)

Where two or more conditions occur at the same time, the precedence is in the order shown above (i.e. receiver linked has the highest priority, followed by VCO error, then internal error).

microcontroller has detected an

internal communications error -

refer to Section 5.7.1

Page 78

B5.4

T855 Fault Finding

M850-00

5.4 DC Checks

5.4.1 Power Rails

Refer to the test points & options diagrams in Section 6 for test point locations, and to the regulator fault finding chart (Section 5.7.2) for fault diagnosis.

Check the 9V (TP602) and 13.8V (TP601) power supply test points in the regulator compartment with a DMM.

Check the 20V regulator output at the test point (TP603) in the regulator compartment.

Check the 5V regulator output at the test point (TP604) in the regulator compartment and on IC310 pin 4.

Check the 5V digital regulator output at the junction of C611A (+) and IC610 pin 2 in the regulator compartment.

5.4.2 VCO Locking

Using a DMM, monitor the VCO control voltage on the long lead of L1 on the VCO PCB.

If the synthesiser is locked and the VCO aligned, the voltage at this point should be between 3 and 16V.

If the VCO is not locked, refer to the synthesiser fault finding charts (Section 5.7.3).

5.4.3 Mute Operation

The front panel "Gate" LED will show the status of the mute circuitry and will turn on when a signal is received above the threshold level.

Check that PL250 is linked correctly:

noise mute 1-2 carrier mute 2-3.

Check that the mute gate opens as follows:

noise mute - rotate RV230 (front panel gating sensitivity) fully clock-

wise and check that the front panel "Gate" LED turns on;

carrier mute - rotate RV235 (carrier mute) fully clockwise and check that

the front panel "Gate" LED turns on.

If the mute fails to operate correctly, refer to the noise mute fault finding chart (Section

5.7.4) or the carrier mute fault finding chart (Section 5.7.5).

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Page 79

M850-00

T855 Fault Finding

5.5 RF Checks

5.5.1 VCO Freque ncy

Check that the VCO is phase locked (refer to Section 5.4.2).

Connect a frequency counter (level +20dBm) to the VCO input to the mixer (IC410).

B5.5

Monitor the local oscillator frequency and check that it is 45MHz required receive frequency.

Refer to the synthesiser fault finding charts (Section 5.7.3) for further information.

below the

5.5.2 RF Sensitivity

Ensure that the VCO is on the correct frequency and the receiver correctly aligned.

Check that the 12dB sinad sensitivity into the front end is as follows:

-117dBm (de-emphasised response)

-111dBm (flat response).

If the sensitivity is poor, you can trace the fault by measuring the sensitivity into successive circuit blocks. Prepare a test cable by connecting a 1nF capacitor to the end of a length of coax cable as shown in Figure 5.1.

1nF

Coax

To Test Cable

Connect To Earth

Figure 5.1 RF Test Cable

Note:

Poor sensitivity indicates a fault in one of the circuit blocks following the test break.

Note:

Refer to the receiver fault finding charts (Section 5.7.6) for further information.

Before using the test cable, ensure the coax braid is connected to an earth point on the PCB.

Using the RF test cable, apply a modulated 45MHz signal to the test breaks in the IF section, or an on-channel RF signal to the front end test breaks.

Check that the sensitivity at each test break is within 2dB of the levels shown on the circuit diagram.

Poor sensitivity into the mixer can be caused by lack of drive level from the VCO (the drive level should be >+17dBm).

Page 80

B5.6

T855 Fault Finding

5.5.3 Oscillator Stability

5.5.3.1 TCXO

While maintaining a low level unmodulated RF input to the receiver, loosely couple into the first IF an additional high level signal at 45MHz - you should now hear a constant low frequency beat note.

Tap the TCXO with a finger and replace it if the beat note permanently changes.

5.5.3.2 Second IF

While maintaining a low level unmodulated RF input to the receiver, loosely couple into the second IF an additional high level signal at 455kHz - you should now hear a constant low frequency beat note.

Adjust L385 for "zero beat".

M850-00

5.5.4 Demodulator Output

Apply an on-channel RF signal modulated by 1kHz with ±3kHz (±2.4kHz) [±1.5kHz] deviation at an amplitude of -65dBm.

Connect an oscilloscope probe (DC coupled) to TP314 (audio output).

Check that an audio signal of approximately 800mV peak to peak is present.

Optimum tuning of the quad coil (L390) for minimum audio distortion (with a "flat" audio response) should coincide with maximum audio amplitude and a DC level of approximately 1.7V.

5.5.5 IF Distortion

If the audio distortion is still high after careful IF alignment (Section 3.7), sweep the IF to investigate the bandpass response.

Apply an on-channel RF signal modulated at 10Hz with ±12kHz (±9kHz) [±6kHz] deviation at an amplitude of -80dBm.

Connect the modulating 10Hz audio signal to the "X" input of an oscilloscope and observe the 455kHz IF input to SK320 pin 3 via a suitable RF probe on the "Y" input. Alternatively, if you have an RSSI PCB fitted, use an oscilloscope probe for the "Y" input to monitor the RSSI output voltage at pad P238 (RSSI test point) or pin 5 of D-range 1 (PL100). This will give a demodulated log response and only the top half of the wave forms shown in Figure 5.2 and Figure 5.3 will be displayed on the oscilloscope screen.

Note:

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The "X" input should be DC coupled.

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M850-00

T855 Fault Finding

Check that the swept response has a rounded top and no sharp non-linearities (refer to Figure 5.2).

Increase the RF level to -50dBm; the trace will now show the shape of the 455kHz ceramic filter (&XF302).

Check that the response has no sharp non-linearities.

If sharp non-linearities do occur, replace the filter and sweep again to confirm a satisfactory solution (refer to Figure 5.3).

B5.7

Figure 5.2 IF Swept Response Figure 5.3 Ceramic Filter Swept Response

Page 82

B5.8

T855 Fault Finding

M850-00

5.6 PGM800Win Generated Errors

The following errors are those most likely to occur using PGM800Win. Refer to the PGM800Win software user’s manual for a complete list of error messages.

Channel Switch Set

The (programmed) default channel change was not accepted by the base station because a channel is selected externally. Try turning the external channel switch off to change the default channel in PGM800Win.

Synth Out Of Lock

The synthesiser received incorrect data, or the data was corrupted. Enter a frequency within the VCO switching range, or tune the VCO.

Internal Error

Data could not be read from the base station due to an internal error. Check for shorts or open circuits on the SDA, SCK, SYNTH and EPOT lines. The SDA, SCK and SYNTH are normally high.

Write/Read To An Unlinked Module

The link to the module does not exist. Undefined error.

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Page 83

M850-00

5.7 Fault Finding Charts

T855 Fault Finding

B5.9

Note:

The standard test point designations used in this section are as follows:

TP601 13.8V TP602 9V TP603 20V TP604 5V

5.7.1 Microcontroll er (IC810)

5.7.1.1 Basic Checks

Is the 12.8MHz clock

present on IC810 pin 21

(microcontroller)?

Replace

IC810.

N Pulsing

Is pin 30 pulsing?

Check the

state of

pin 10.

High or open circuit

Low

Check IC740 (synthesiser).

Use a DSO* to check

operation of IC650

(i.e. active high

pulse at power up).

*digital storage oscilloscope

Replace

IC650.

Check state of

pins 36 to 43.

Static high/low

Replace IC810.

Pulsing

Check state

of pin 35.

Correct the fault causing pin 35 to be low/floating.

High

Low/floating

Replace

IC810.

Page 84

B5.10

T855 Fault Finding

5.7.1.2 Serial Communication

M850-00

Disconnect the

pro

ramming lead.

Is IC810 pin 11 hi

(microcontroller)

Connect the programmin

lead and use PGM800Win

to read the rack/radio.

Check I/O pad P810

with a DSO*.

Does it swin

oscilloscope

Use PGM800Win

to send a POLL command to the

from

0 to 5V?

Y*digital storage

radio.

Check pin state.

Noise

on pin

Check the SERIAL-COM

and AUDIO-1/2 links.

Check the transistor

interface circuitry

and/or replace the

ramming lead.

pro

Low/floatin

Check the transistor

interface circuitry.

Check IC810 pin 13

with a DSO. Is there

a response from IC810 after

a poll command is sent?

Check the transistor

interface circuitry

and/or replace the

ramming lead.

pro

Replace

IC810.

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Page 85

M850-00

5.7.1.3 CTCSS Decode

T855 Fault Finding

B5.11

Use PGM800Win to

select a channel

with a CTCSS tone

rammed.

pro

Set test equipment to correct

channel/CTCSS tone.

Check IC830 pin 7.

Is there a square wave at

the CTCSS input frequency?

Check IC810 pins 24 & 26

(microcontroller).

Are there 5V square waves at

the CTCSS frequency?

Check IC850 pins 1 & 14.

Are there 9V square waves at

the CTCSS frequency?

Cannot select a channel

No square wave or

uneven mark/space ratio

No square waves or

uneven mark/space ratio

No square waves or

uneven mark/space ratio

Check serial communications.

(See separate flow chart).

Check the input filter is operatin

Replace IC810.

Replace IC850.

correctly

(IC830 pin 8).

Is IC850 pin 7 low and

Q845 collector hi

Is IC810 pin 31 low? Replace IC810.

Check the receiver

mute circuit.

Replace IC850

or Q845.

Page 86

B5.12

T855 Fault Finding

5.7.2 Regulator

M850-00

Check for

overheatin

components &

short circuits.

13.8V present on IC630 pin 3?

5.3V present on IC630 pin 1?

9.0V present

on TP602?

20V present

on TP603?

Check continuity

from D-ran

connector pin 9.

(D-ran

Replace IC630.

Check Q620,

Q630 & IC640.

Check Q660 is

switchin

approx. 180kHz.

e 1)

5V present on

IC610 pin 2?

Regulators OK.

Check R615.

Replace IC610.

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Page 87

M850-00

T855 Fault Finding

B5.13

5.7.3 Synthesiser

Refer to the synthesiser circuit diagram (sheet 7) in Section 6 and the VCO circuit diagram in Part E.

No VCO RF output.

9V present at VCO Q4/Q5?

DC V present

at Q4 & Q5?

8.3V present at VCO?

DC V present at

VCO, Q1, Q2 & Q3?

Capacitors OK?

Check for cracks,

shorts, etc.

VCO out of lock.

Check 9V reg.

Check biasin

resistors, Q4 & Q5.

Check Q4 C

multiplier

(synth).

Check biasin

resistors, Q1,

Q2 & Q3.

Replace

if faulty.

+5V present

at IC700, IC710

& IC740?

20V present

on IC750 pin 8?

9V present on

Q795 divider buffer?

DC V present

on Q795 emitter?

Does VCO trimmer

adjust for stable

control line between

3 & 16V?

Check 5V reg. &

supply resistor

to each IC.

20V inverter

supply faulty.

Check 9V supply.

Check biasin

resistors & Q1.

Replace VCO.

Check VCO tunin

caps & trimmer.

Check #C1, L1, L2,

D1 & D2 in VCO.

VCO trimmer

freq. ran

Is 8MHz VCO range

achieved between

Continued on the next pa

e OK? Y

3 & 16V?

VCO OK.

VCO freq. correct?

Does VCO trimmer

adjust for required

frequency ran

between 3 & 16V?

Synthesiser OK.

Recheck

pro

rammin

via PGM800Win.

Page 88

B5.14

T855 Fault Finding

Continued from previous page

M850-00

Replace synthesiser

(IC740).

Check phase detector output

pins (IC740 pins 3 & 4).

Are there very narrow pulses

(~50ns) at the reference frequency?

(i.e. 5kHz : 200µs period

6.25kHz : 160µs period) *See Note below.

Is the charge pump bias

voltage at the base of

Q760 & Q780 between

3.5 and 5V? (5V when locked) Y

Is the voltage on C762,

R760, and R758 9V ±0.2V?

Is the charge pump voltage

on Q790 gate between

3 and 8.5V? (6.5V ±0.2V locked)

Is the loop filter reference

voltage at C772 (+) 6.5V ±0.2V?

Check programming.

N Y

Check serial bus

when programming

i.e. clock/data/enable

activity (IC740 pins

18, 19 & 17).

Check Q760, Q780,

R766 & C765.

Check R762 & C762.

Check charge pump components

(Q775 & Q780) and Q790.

Check C772, R774, R772,

C770, R763 & Q790.

Programming and

serial bus OK?

Check microcontroller

section (IC810).

Is reference

clock present

at IC740 pin 20

(12.8MHz >1.5Vpp)?

Check TCXO (IC700)

and buffers (IC710).

Check loop filter components

R775, C774, C776, R510, C505, IC750. Is the supply

to IC750 +20V +4, -2V?

Check the signal path from

the VCO to synthesiser.

Measure the frequency from

the VCO at IC740 pin 11 using

a frequency counter.

Signal

Is the level >-10dBm?

Does the frequency adjust

as the VCO trimmer is

adjusted (out of lock)?

Replace synthesiser

(IC740).

No signal

Check regulator circuitry.

Check VCO.

Check divider buffer

circuit (Q795) and bias

voltages on Q795 emitter

(1.3V ±0.2V).

*Note:

When locked, both of these are very narrow (~50ns). If unlocked, one will be very narrow (~50ns), and the other wide (>15µs).

31/09/98 Copyright TEL

Page 89

M850-00

Noisy synth; poor

selectivity &/or

poor residual FM.

T855 Fault Finding

B5.15

VCO phase locked?

3-16V present on

control line?

Correct DC V

present on Q1 VCO?

Loop filter &

components around

op. amp. (IC750) OK?

Change trimmer;

still noisy?

Change Q1;

still noisy?

Go to B.

Check inductors, biasin

resistors

& Q1.

Replace if faulty.

Change TCXO;

still noisy?

Change varactors;

still noisy?

Replace VCO

assembly.

Synthesiser OK.

Page 90

B5.16

T855 Fault Finding

5.7.4 Noise Mute

M850-00

Ensure PL250 is set

for noise mute operation.

Rotate RV230 (gating sensitivity) c/w & cc/w & view

"Gate" LED.

Does "Gate" LED

toggle on/off?

Switch SW201 (monitor

mute) to ensure

mute is enabled.

Check Q230, Q245 &

Q290 for operation.

Mutable audio

on outputs?

Refer to audio fault finding chart.

Apply on channel signal

@ -117dBm* to receiver.

Audio on

TP314?

Noise on

IC310 pin 11?

Amplified noise

on C380?

Approx. 0.6V DC rect-

ified noise on pad 236?

Vary RF level &

observe voltage

on pad 236.

Pad 236 voltage

varies 0-1.8V?

Adjust RV230 (gating sensitivity) & observe voltage

on IC270 pin 3.

*Modulated by 1kHz signal with ±3kHz (±2.4kHz) [±1.5kHz] deviation

Check components around active filter.

Check D310 is

rectifying noise.

Check RV330

(noise mute gain).

Refer to receiver fault finding chart.

Check Q340

& Q350.

adjustment

Note:

c/w = clockwise cc/w = counterclockwise or anticlockwise

Voltage varies

0-2.5V?

Set RF signal level to

-117dBm. Rotate

RV230 c/w & cc/w.

Monitor voltage on

IC270 pin 1. Switching

0-8V as RV230 rotated?

Monitor voltage on

IC270 pin 7. Switching

0-8V as RV230 rotated?

Monitor voltage on

pad 234. Switching

0-8V as RV230 rotated?

Does "Gate" LED toggle?

Check 9V rail &

resistors R264,

R265 & R284.

Replace IC270.

Check/replace

IC270 & D240.

Replace Q250.

Check/replace Q255 & D250.

31/09/98 Copyright TEL

Page 91

M850-00

5.7.5 Carrier Mute

Ensure PL250 is set

for carrier mute operation,

and the RSSI PCB is fitted.

T855 Fault Finding

B5.17

Switch SW201

(monitor mute) to ensure

mute is enabled.

Apply on channel signal

@ -110dBm* to receiver.

Audio on

TP314?

Approx. 2V at

D-Range 1 pin 5?

Rotate RV235

(carrier mute) c/w & cc/w

& view "Gate" LED.

Does "Gate" LED

toggle on/off?

Approx. 5V on

RSSI pad 238?

Approx. 5V on

IC280 pin 1?

*Modulated by 1kHz signal with ±3kHz (±2.4kHz) [±1.5kHz] deviation.

Refer to receiver fault finding chart.

Check for short circuits

and/or replace IC310.

Check Q340 and

adjoining components.

Check/replace IC280

& adjoining components.

Check Q230, Q245 &

Q290 for operation.

Note:

c/w = clockwise cc/w = counterclockwise or anticlockwise

Mutable audio

Refer to audio

fault finding chart.

on outputs?

Adjust RV235 & observe voltage

on IC280 pin 6.

Voltage varies

0-6V?

Set RF signal level

to -95dBm. Rotate

RV235 c/w & cc/w.

Monitor voltage on

IC280 pin 7. Switching

0-8V as RV235 rotated?

Monitor voltage on

IC270 pin 7. Switching

0-8V as RV235 rotated?

Monitor voltage on

pad 234. Switching

0-8V as RV235 rotated?

Does "Gate" LED toggle?

Check 9V rail & resistors R275, R277 & RV235.

Replace IC280.

Check/replace IC270 & D240.

Replace Q250.

Check/replace Q255 & D250.

Page 92

B5.18

T855 Fault Finding

5.7.6 Receiver

Refer to the receiver IF and front end circuit diagrams (sheets 3 & 4) in Section 6.

Poor sensitivity:

worse than -117dBm.

Ensure VCO, RF

front end & IF

correctly aligned.

M850-00

High audio

distortion.

Quad coil L390

tuned for min.

distortion (flat

audio response)?

Check VCO

frequency OK?

Check IF

alignment OK?

Check distortion

TP314 OK?

Fault find audio.

High audio

distortion?

Check DC

conditions OK?

(see cct diagrams)

Adjust L390.

Retune all

IF coils.

Readjust TCXO

frequency.

Adjust IF coils.

Check distortion

TP314,

injecting 45MHz

@ -47dBm into TP310

at Q320 input. OK?

Inject 45MHz after mixer IF

output TP412.

Measure distortion.

OK?

Check sensitivity

into each stage

(see 5.5.2)

Check/repair faulty

stage or component.

Fault in IC310,

&XF302, Q330,

Q320, &XF301 or

surrounding circuitry.

Check/replace.

Check

sensitivity

into each

IF stage.

See Chart B

(below).

Replace

faulty device.

Repair stage.

Inject on-channel

RF into mixer TP411.

Measure distortion.

OK?

Check TCXO

stability OK?

(see 5.5.3)

Replace TCXO.

Refer to synthesiser fault finding

charts.

31/09/98 Copyright TEL

Page 93

M850-00

5.7.7 Audio

T855 Fault Finding

B5.19

Apply on channel signal

@ -117dBm* to receiver.

Audio on

TP314?

Audio on

IC210 pin 1?

Audio at

top of RV205

& RV210?

Ensure RV230

(

ating sensitivity)

fully clockwise.

"Gate" LED on?

*Modulated by 1kHz signal with ±3kHz (±2.4kHz) [±1.5kHz] deviation.

Check components

around IC210.

Check link PL240.

fault findin

Refer to

receiver fault

chart.

findin

Check C233.

Refer to mute

charts.

Audio on

C238/C259?

Audio on

IC240 pin 2 &

IC260 pin 2?

Audio on speaker?

Audio on line

monitor (pad 284)

& line output?

Refer to mute

fault findin

Replace C249 & check continuity.

Check/replace

output components.

charts.

Replace

faulty IC.

Page 94

B5.20

T855 Fault Finding

M850-00

31/09/98 Copyright TEL

Page 95

M850-00

6 T855 PCB Information

T855 PCB Information

B6.1.1

Caution:

This section provides the following information on the T855 receiver:

•parts lists

• grid reference indexes

• mechanical assembly drawings

•PCB layouts

• test points & options connections drawings

• circuit diagrams.

This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.

Section Title IPN Page

6.1 Introduction 6.1.3

6.2 T800-04-0000 RSSI PCB 220-01138-00 6.2.1

6.3 T855 Receiver PCB 220-01396-02 6.3.1

Page 96

B6.1.2

T855 PCB Information

M850-00

31/09/98 Copyright TEL

Page 97

M850-00

T855 PCB Information

B6.1.3

6.1 Introduction

Product Type Identification

You can identify the receiver type by checking the product code printed on a label on the rear of the chassis (product codes are explained in Section 1.3 in this Part of the manual, and Figure 1.1 in Part A shows typical labels). You can further verify the product type by checking the placement of an SMD resistor in the table that is screen printed onto the top side of the PCB, similar to the example drawn below. In this example, the resistor indicates that the product was built as a T855-10-XXXX.

855-30 PRODUCT TYPE 855-35 855-10 855-20 855- 855-13 855-23

PRODUCT TYPE 855-15 855-25

Note:

The only function of this resistor is to indicate the product type. It has no effect on the circuitry or operation of the receiver.

PCB Identification

All PCBs are identified by a unique 10 digit “internal part number” (IPN), e.g. 220-01390-02, which is screen printed onto the PCB (usually on the top side), as shown in the example below:

The last 2 digits of this number define the issue status, which starts at 00 and increments through 01, 02, 03, etc. as the PCB is updated. Some issue PCBs never reach full production status and are therefore not included in this manual. A letter following the 10 digit IPN has no relevance in identifying the PCB for service purposes.

Note:

It is important that you identify which issue PCB you are working on so that you can refer to the appropriate set of PCB information.

Page 98

B6.1.4

T855 PCB Information

M850-00

Parts Lists

The 10 digit numbers (000-00000-00) in this Parts List are “internal part numbers” (IPNs). We can process your spare parts orders more efficiently and accurately if you quote the IPN and provide a brief description of the part.

The components listed in this parts list are divided into two main types: those with a circuit reference (e.g. C2, D1, R121, etc.) and those without (miscellaneous and mechanical).

Those with a circuit reference are grouped in alphabetical order and then in numerical order within each group. Each component entry comprises three or four columns, as shown below:

circuit reference lists components in alphanumeric order

variant column indicates that this is a variant component which is fitted only to the product type listed

description gives a brief description of the component

Internal Part Number order the component

this number

The miscellaneous and mechanical section lists the variant and common parts in IPN order.

Parts List Amendments

At the front of the parts list is the Parts List Amendments box (an example of which is shown below). This box contains a list of component changes which took place after the parts list and diagrams in this section were compiled. These changes (e.g. value changes, added/deleted components, etc.) are listed by circuit reference in alphanumeric order and supersede the information given in the parts list or diagrams. Components without circuit references are listed in IPN order. The number in brackets at the end of each entry refers to the Tait internal Change Order document.

IPN of new

component

Parts List Amendments

R306 Changed from 180Ω to 560Ω (036-13560-00) to increase sensitivity (71003).

Change Order

number

circuit reference

or IPN

31/09/98 Copyright TEL

description

of change

Page 99

M850-00

T855 PCB Information

B6.1.5

Variant Components

A variant component is one that has the same circuit reference but different value or specification in different product types. Where two products share the same PCB, the term “variant” is also used to describe components unplaced in one product. Variant components have a character prefix, such as “&”, “=” or “#”, before the circuit reference (e.g. &R100).

The table below explains the variant prefixes used in T800 Series II products:

If the variant prefix is. . . the component will. . .

& change according to channel spacing

= change according to frequency stability

# change according to frequency range

% be placed or unplaced for special applications

be unplaced in one product (where two products share the same PCB)

Grid Reference Index

This section contains a component grid reference index to help you find components and labelled pads on the PCB layouts and circuit diagrams. This index lists the components and pads in alphanumeric order, along with the appropriate alphanumeric grid references, as shown below:

PCB layout components listed in alphanumeric order

reference

circuit diagram

reference

component location on the sheet

sheet number

component location on the layer

layer number 1 = top side layer 2 = bottom side layer

Page 100

B6.1.6

t s

T855 PCB Information

M850-00

Using CAD Circuit Diagrams

Reading a CAD circuit diagram is similar to reading a road map, in that both have an alphanumeric border. The circuit diagrams in this manual use letters to represent the horizontal axis, and numbers for the vertical axis. These circuit diagram “grid references” are useful in following a circuit that is spread over two or more sheets.

When a line representing part of the circuitry is discontinued, a reference will be given at the end of the line to indicate where the rest of the circuitry is located, as shown below. The first digit refers to the sheet number and the last two characters refer to the location on that sheet of the continuation of the circuit (e.g. 1R3).

hese grid references

how where the circuit

is continued

DISCRIMINATOR

1R3 2R9 2R9 8A2

IF-SIG

4R4

%R338

100

C301

4N7

C369 100P

L310 33U

C371

10U

R339 100K

R303

31/09/98 Copyright TEL

Tait TEL0024, TEL0025, TEL0022, TEL0021, TEL0020 Descriptions Diagrams Info

Specifications and Main Features

Frequently Asked Questions

User Manual

About This Manual

Updating Equipment And Manuals

Copyright

Ordering Tait Service Manuals

Publication Information

Table Of Contents

List Of Effective Pages

Part A Introduction To Servicing

1 General

1.1 Additional Technical Information

1.2 Caution: CMOS Devices

1.3 Caution: Aerial Load

1.4 Caution: Beryllium Oxide & Power Transistors

2 Mechanical

2.1 Torx Recess Head Screws

2.2 Pozidriv & Philips Recess Head Screws

2.3 Disassembly/Reassembly

2.3.1 Receivers/Exciters/Transmitters

2.3.2 Power Amplifiers

2.4 Cover Screw Torques

3 Component Replacement

3.1 Leaded Components

3.1.1 Desoldering Iron Method

3.1.2 Component Cutting Method

3.2 Surface Mount Devices

3.3 Cased Mica Capacitors

4 Software History

4.1 PGM800Win V1.0

4.2 PGM800Win V2.00

Part B T855 Receiver

1 T855 General Information

1.1 Introduction

1.2 Specifications

1.2.1 Introduction

1.2.2 General

1.2.3 RF Section

1.2.4 Audio Section

1.2.4.1 General

1.2.4.2 CTCSS

1.2.4.3 Mute Operation

1.2.5 Microprocessor Controller

1.2.6 Test Standards

1.2.6.1 European Telecommunication Standard

1.2.6.2 DTI CEPT Recommendation T/R-24-01

1.2.6.3 Telecommunications Industry Association

1.3 Product Codes

1.4 Standard Product Range

2 T855 Circuit Operation

2.1 Introduction

2.2 Receiver Front End

2.3 Mixer

2.4 IF Circuitry

2.5 Noise Mute (Squelch)

2.6 Carrier Mute

2.7 Audio Processor

2.8 Power Supply And Regulators

2.9 Microcontroller

2.10 Synthesised Local Oscillator

2.11 VCO

2.12 Received Signal Strength Indicator (RSSI)

3 T855 Initial Tuning & Adjustment

3.1 Introduction

3.2 Channel Programming

3.3 Test Equipment Required

3.4 Short Tuning Procedure

3.4.1 Introduction

3.4.2 Synthesiser Alignment

3.4.3 Front End Alignment

3.4.4 Mute Adjustment

3.4.4.1 Noise Mute

3.4.4.2 Carrier Level Mute

3.4.5 Line Amplifier Output

3.4.6 CTCSS

3.4.6.1 Decoder Operation

3.4.6.2 Opening Sinad

3.4.6.3 High Pass Filter