Arcam T51 Service Manual

Service Manual

DiVA T51 AM/FM Tuner

T51

Issue 1.0

ARCAM

Contents List

Contents list

Circuit description

Circuit diagrams

Component overlays

Circuit board parts list

General assembly parts list

T51 Tuner Circuit Description

Power Supply

Mains voltage selection is made by placing a fuse, of appropriate value, in the 115V or 230V position. The single secondary is rectified and regulated and supplies four regulat ors.

Z7 is always powered when the mains is connected and keeps the pr eset memory of the micro controller intact. The high-value capaci tor (C84) will keep this data sa fe, for a limited time, in case of mains power failure.

Z5 provides the main 12V supply rail for the RF and audio circuits. This is always connected, except for the supply to the FM front end, which is di sabled by Q2 when t he unit is turned 'off'.

Z4 powers the LED back light on the display PCB.

Z6 is the 5V digital supply for the micro controller.

FM Tuner & IF

The FM aerial input is mixed in the front end FE1 which provides a 10.7MH z IF output. This is filtered and amplified by ceramic filters CF1 & CF2 and the circuit based around Q9 & Q10. A third filter CF3 can be put in circuit by fitting jumpers JP1 & JP2 across pins 2 & 4 and 1 & 3 of SK6 respectively. This effectively narrows the IF band to improve selectivity. Transistors Q17 and Q21 are part of the AGC circuit. The po sition of the jumper link JP7 to either SK10 or SK11 determines from which point the AGC circuit is triggered. The default is for the jumper to be fitted to SK10 which minimizes cross modulation and prevents the IF amp becoming saturated.

The LA1266 (Z9) demodulates the IF at pin 1 into an audio output at pin 12. The quadrature coil is a double-tuned device for best distortion perform ance.

When a station is tuned correctly the 'On Tune' signal goes low and drives a green LED on the display PCB. This signal is also used by the auto-stop detection and muting circuits.

AM Tuner & IF

The LA1266 (Z9) contains the AM RF amplifier, oscillator and mixer circuitry.

Switching between FM and AM modes is controlled by the 'FM' signal from the micro controller which disables the AM circuitry of Z9 and switches th e path of the audio signal throug h Z8.

MW/LW switching is performed by switching transistors Q12, Q14 & Q15. Each band has its own oscillator and aerial tuning coils, tuned by a varica p diode all contained within the AM module L5.

The 450kHz IF signal is fi ltered by coil and ceramic filter combination T5.

Birdie Filter

The ‘Birdie Filter’ (L2) is a four pole low pass filter, flat to about 53kHz, then with a very steep roll off from then on.. This is designed to reduce co-channel interference in FM Stereo and cut down on irritating ‘birdie’ noises.

Stereo Decoder

Stereo decoding is performed by LA3401 (Z8). The 38kHz reference signal is accurately created by ceramic resonator X3 and does not require adjus t ment. Stereo sepa ration is adjusted for maximum by preset RV1. This IC also contains FM/AM audio switching and muting functions.

Audio Filter s & Output

The left and righ t channel audio out puts from Z8 are filtered by the de-emphasis network of R1, C1 etc. The correct de-emphasis network is selected by the position of jumpers JP3 & JP4 on the pins of SK8. C2 & C102 (220pF) are selected for 50us and C3 & C103 (560pF) for 75us de-emph a sis .

The final filter, based on Z3, is a two-pole low-pass circuit with a cut-off frequency of around 20kHz. Also included is a 19kHz notch filter, L1 & C4, that removes most of the residual pilot to ne.

Muting

When the power switch is turned off Q5 is switched off, enabling the mute circuitr y of the stereo decoder (Z8) via diode D9. This rem oves the need for output muting transistors and elimin ates switchin g clicks and pops . At switch-on the mute is enabled while C21 is charged via Z8.

In normal use the mute inside Z8 is enabled in three other ways:

The AMUTE signal from the mic r o controller is active at power-on and for a short t ime when a preset is changed. When the band is changed the output is muted by charging C52. The audio outpu t must be muted whenever the tuner is in stereo mode and is also off-tune. This is to eliminate no ise during tuning and is provided by Q8 and the MONO and OFF TUNE control signals. In Mono mode this mute is disabled so that weak stations can be heard, despite the noise.

Micro controller

Control of the DiVA T51 tuner is performed by a single micro controller Z10, LA7230. This also provides keypad input and drives a LCD directly.

At power-on a matrix of diodes is scanned to set-up the controller for the correc t options:

D7 selects the correct frequency ran ges.

D10 enables the use of Auto tuning as well as manual tuning.

D8 allows the Auto-tuning mode to use the ‘IF Count’ method of search ing.

The position of jumpers JP 5 & JP6 fitted to SK9 are used to disable or enable LW and also whether the AM band steps are 9 kHz (UK) or 10 kHz (USA).

Z10 provides cont rol s ignal outputs for the following functions:

MONO - To defeat the stereo decoder

AMUTE - Turns on the mute circuit when a button is pressed & during tuning.

FM, MW & LW - Only one output active low at any one time. Used to switch on specific parts of the RF circuitry as appropriate.

The micro controller incl udes a Phase-Locked-Loop (PLL) circuit which compares the tuner local oscillator signals (FMIN & AMIN) with a reference frequency. B ased on this information and the required tuned frequency the controller varies the tuni ng voltage to the FM and AM front ends.

The tuning voltages (FMVt & AMVt) have to be filtered from the PLL by the circuitry around Q7 & Q13.

Display PCB

The display PCB holds the keypad, LCD display, LED back light modu le and On-Tune indicator.

The remote control receiver consists of the receiver RX1 and the PIC micro controller, Z1, which is used to decode the incoming remote control codes from RC5 format to Sanyo type commands. This is because the Sanyo micro controller, Z10, can only respond to Sanyo remote control commands.

Jumper Settings

Jumper Option 1 Option 2

JP1 Best sensitivity Best sound JP2 Best sensitivity Best sound JP3 De-emphasis 50uS De-emphasis

75uS

JP4 De-emphasis 50uS De-emphasis

75uS JP5 LW & MW MW only JP6 AM spacing 9KHz AM spacing

10KHz JP7 Less X-MOD Less De-sense

USA / Rest of the World

If the T51 is transferred from or to the USA the following jumper settings will require changing.

Jumper Rest of the

World

JP3 50uS 75uS De-emphasis JP4 50uS 75uS De-emphasis JP6 9KHz 10KHz AM spacing

USA Action

87654321

LK22

LK23

LK24

LK25

LK26

LK27

LK31

LK32

LK33

LK34

LK35

LK36

LK37

LK41

LK43

LK44

LK45

LK46

LK47

LK51

LK52

LK53

LK54

LK55

LK56

LK57

FM/AM IF Demodulator L892C2_1_2.SCH

Stereo decoder and Audio L892C3_1_2.SCH

LK18

LK19

LK20

LK28

LK29

LK30

LK38

LK39

LK40

LK48

LK49

LK50

LK58

LK59

LK60

LCTR HCTR IFCNT LO

SD AMIN SCAN

AMVt FMVt

Microprocessor and PLL L892C4_1_2.SCH

FMVt AMVt

SCAN AMIN SD

LO IFCNT HCTR LCTR

OFF TUNE

Power Mute

AM Audio FM Audio

ON TUNE

PICMUTE

STEREO

MONO

AMUTE

AM Audio FM Audio

Power Mute FM

AMUTEOFF TUNE

MONO

STEREO

PICMUTE

Tooling & Fixing Holes

Tooling Holes

PD1

TOOLING

PD2

TOOLING

PD3

TOOLING

PD4

TOOLING

EL1

Update Box

UPDATE_BOX

Main PCB Fixing Holes

FIX1 FIX2 FIX3 FIX4FIX5

FIX6 FIX7 FIX8

Photo Strip

PHOTO_STRIP

Photo Block

PHOTO_BLOCK

DD4

PCB MATERIAL

CEM1, 2 OZ Cu

CEM1_20Z

DRAWING TITLE

T51 Tuner

PCB

T100MASP

L892PB_1

PCB

EL10

Cable

Tie

CABLE_TIE

DD1

Drilling

Detail

DRILL_DWG

Kit Mask Exclude 'NF' parts from kit mask, i.e. Not Fitted.

This applies to R4 and R104

DD2

A2 Vertical

Paper Marker

DD_A2V

DD3

A2 Horizontal

Paper Marker

DD_A2H

Circuit Diagram

Notes:

00_1078

A & R Cambridge Ltd. Pembroke Avenue Denny Industrial Centre Waterbeach Cambridge CB5 9PB

1 2 3 4 5 6 7 8

Filename

G:\DATA\ECO\ECO AGENDA\00_1078 L892 T51 TUNER\L892_1\L892_1.ddb - L892c1_1_2.prj

ECO No. DESCRIPTION OF CHANGE

Date Printed

CL 12/09/00 R93 WAS 220R NOW 1K0

CL 17/7/00 PRODUCTION RELEASE00-1044

INITIALS

12-Sep-2000

DATE

Drawn by:

1 4Sheet of

DRAWING NO.

1.2

ISSUE

L892CT

+ 10 hidden pages