Intek M-760 Service Manual

Model No: M760 Plus

Customer: INTEK Rev No: A

M-760 Plus

Service Manual

Model No: M760 Plus

Customer: INTEK Rev No: A

Table of Contents Page

Specifications …………………………………………………………….……3 Test and Alignment Procedure ……………………………………….….…….4 Block Diagram ………………………………………………………….……13 Schematic Diagram ……………………………………………….………. 14 Printed Circuit Board ……………………………………………………… 21 Channel Frequency Charts ……………………………………….…………23 Parts List ……………………………………………………………………32 Semiconductor Voltage Chart ………………………………………………...38

Model No: M760 Plus

Customer: INTEK Rev No: A

SPECIFICATIONS

1. GENERAL

Channels………………………...…………………………….................. …….400 Ch AM/FM 4W

Frequency Range………………………………...……………… …. …..…25.615 to 30.105 MHz FrequencyControl……………………………………………………..…………..……………..…PLL Operating Temperature Range……………………..……………………………….…-10° / +55°C

DC Input Voltage…………………………...……………………………………....13.2 V DC ±15%

Size………………………………………….……………..……….…180(L) X 35(H) X 140(D) mm Weight……………………………………………………..………………..……...…………0.850 kg

2. RECEIVER

Receiving System……………………………..Dual Conversion Super Heterodyne Intermediate Frequency…………………………………………………….…1st IF: 10.695 MHz, 2nd IF: 455 MHZ

Sensitivity……………………………………….....….0.5 µV for 20 db SINAD in FM mode Audio

Distortion……………………………………..………..……..…………….Less Than 8% @ 1 KHz ImageRejection………………………………………………………………………..………...65 dB Adjacent ChannelRejection…………………………………………….……………………...65 dB Signal/ Noise Ratio………………………………………………………………………….….45 dB Current Drain at standby……………………………………………………………………..325 mA

3. TRANSMITTER

Output Power……………………………………………………..……….....….4W @ 13.2 V DC

Modulation……………………………………………………...…….……FM: 1.8 KHz ±0.2 KHz

Frequency response…………………………………………………....From 400 Hz to 2.5 KHz

Output impedance…………………………………..…………………………………RF 50 ohm Unbalance Signal/ Noise Ratio……………………………………………………………..40 dB MIN Current Drain…………………………………………………………………….….1300 mA

Model No: M760 Plus

Customer: INTEK Rev No: A

OPERATION INSTRUCTIONS

Having properly installed your batteries and hooked-up the antenna, you are now ready to operate your radio for optimum reception and voice transmission.

Turn the power “ON” with ON/OFF switch.

Set the desired channel.

Adjust the squelch control knob to reduce any undesirable background noise when no signal is being received. To do this, select a channel where no signal are present, or wait until signals cease on your channel. Then, rotate the squelch control knob clockwise to a point where the background noise disappears.

Note: When the squelch is set properly, the speaker will remain quiet until a signal is received. In order to receive weak signals, do not set the squelch too high.

Adjust the volume to the desired listening level.

To Transmit

Press and hold the push-to-talk button. Speak slowly and clearly in a normal voice two to three inches from the microphone. A buit-in modulation control circuit will automatically adjust the microphone input level. There is no need to speak loudly.

To Receive

Release the push-to-talk button.

Model No: M760 Plus

Customer: INTEK Rev No: A

THEORY OF OPERATIONS

TRANSMITTER

A. RF Amplification

The output of double AMP Q14 is fed through tuning IFT L8 to the base of pre driver AMP Q15. The output is then supplied through tuning circuit L9 to RF driver AMP Q16. The output of Q16 is supplied with tuning circuit L10 and C116,C67,C95 and goes to the base of final RF AMP Q17. The output of Q17 is supplied to the antenna through L-C tuning circuit.

B. Circuit for Suppression of Spurious Radiation

The tuning circuit between the output of final AMP Q17 and antenna, 4-stage “PHI” network L13, C142,C71,C72,L14,C74,C75,L15,C77,C78,L16,C79,C80,L24 serves as a spurious radiation suppressor . This network also serves to match the impedance between TX power AMP Q17 and the antenna.

C. Circuit for Limiting Power

After finished all alignment, the constant voltage supply circuit limits the available power 4 W or slightly less.

RV4 and corresponding three transistors control supply voltage of RF amplifier and other circuits. Tune all the trimmer parts for maximum indication of RF power meter and adjust RV4 to make 4 w indication of

RF power meter. The tuning is adjusted so that the actual power is from 3.5 to 4.0 W. There are no other additional controls for

adjusting the TX output power.

D. Modulation Control

a. FM The mic input is fed to mic audio amplifier IC KIA324 which drives modulation varicap diode D403 in the VCO

circuit. RV1 limits the incoming modulation audio levels to inhibit over modulation. While reading the modulation factor on the modulation analyzing equipment, adjust RV1 shall not exceed +-1.7 KHz/Dev. After 20 dB up from

1.25 KHz/1.2 KHz/Dev. Audio level b. AM

Modulation signals are filtered with RC network and goes to the audio power AMP IC IC103 to make nominal signal level to achieve wanted modulation. To control incoming audio signal, diode D7 and corresponding ALC circuit limits the modulation shall not exceed +/-90% adjust RV3 +/-90% modulation under 1.0 KHz AF 60% mod plus 20 dB of audio signal.

Model No: M760 Plus

Customer: INTEK Rev No: A

E. Receiver

CB receiver is dual conversion supper-heterodyne type with the first IF 10.695 MHz and second IF 455 KHz. Receiver is separated two blocks, 1

IF section and 2nd IF section. The PLL synthesizer supplies first local frequency 16.270 ~ 16.710 MHz.(for EU) and 16.90625 MHz ~ 17.29625 MHz (for UK) With the provided first local frequencies to Q2,Q3 mixes the incoming RF signal to generate first IF signal. Mixed signals were filtered with the XF1 (10.695 MHz) crystal filter and other tuning circuits. Output signal of mixer is filtered with CF1(455

KHz ceramic filter). The 455 KHz signal from the 2

IF filter was amplified and limits internaly. After amplification the signals fed the quadrature detector loop L20. Then we can see the recovered audio signals on Pin 9 for FM of IC7. With the amplitude of recovered signals, Q10 serves as an audio amplifier. For AM signal Will be pass filter CF1 and induced to Q6, Q7 respective and detected to voice signal by D5.

TROUBLESHOOTING HINTS

Symptom

Unit does not work at all

Probable Cause Remedy

• Defective power switch VR1. • Blown fuse. • Broken DC power cord. • Defective IC5.

• Replace • Replace • Replace • Replace

No output from speaker at all

No noise on speaker

Squelch does not work

• Defective external speaker jack. • Poor connection on microphone connector • Defective push switch on microphone. • Defective internal speaker. • Defective VR1, IC8 other components.

• Measure all the voltage of IC7 with voltage chart • Defective squelch circuit components (RV5,RV7,VR2 IC7)

• Defective VR2, RV5,RV7, IC3-D.

• Repair or replace •

Repair or replace • Repair or replace • Replace • Replace the defective components.

• Replace • Replace

• Replace the defective

components. • Re-adjust

Model No: M760 Plus

Customer: INTEK Rev No: A

No modulation

• Defective microphone. • Poor audio output and defective modulation microphone amplifier components (IC3). • Defective microphone connector components. • Defective ALC circuit D8,D9

• Replace • Replace the defective components. • Replace • Replace the defective components.

LCD meter does not work

LCD display does not work

Channel selector does not work

EMG CH9.19 does not work

• Defective D11,D22 • Defective IC5. • Defective RV2.RV6

• Defective RED wire fuse. • Defective IC5, .

• Defective IC5. • Replace

• Defective EMG SW. • Defective IC5. • Replace • Replace

• Replace • Replace •

Replace

• Replace • Replace

TEST EQUIPMENT SETUP

A. TX test equipment setup:

Spectrum Power Analyzer Supply

Modulation Wattmeter Radio Meter 10W U.U.T.

Oscilloscope Frequency Audio Gen. Counter

Distortion AC Meter Voltmeter

Model No: M760 Plus

Customer: INTEK Rev No: A

B. RX test equipment setup:

SINAD Meter RF Signal Power Generator Supply

Distortion 8 ohm Radio Meter loading U.U.T.

Oscilloscope Note: U.U.T. = device under test

Alignment Procedure.

4.1 VCO Adjust.

4.1.1 VCO Voltage Adjust:

Test point TP1 connect to the multi-meter，set UUT enter test mode. Press channel “UP” key to select CH01A of Poland Band in FM mode.

1. Adjust IFT L17 for 1.0 ± 0.1V on the Multi-meter read，and then checking CH40L of RU Band should be less than

3.8V, and then check AM mode CH01A ≥ 0.8V，CH40L ≤ 3.8 V

2. Set UUT for TX MODE：Check CH01A ≥ 0.8V，CH14D ≤ 3.8V; CH15D ≥ 0.8V, CH21G ≤ 3.8V; CH22G ≥ 0.8V,

CH40L ≤ 3.8V.

3. Turn to AM mode and repeat above item 2.

4.2 RX Section Alignment . ( FM and AM )

4.2.1 Audio Distortion Adjust:

1. UUT set to FM mode CH19，output of RF signal generator connect to TP2. Audio dummy load connect to EXT.

Speaker. (@8Ω load)

2. Set RF S.S.G Freq.: 10.695MHz，Mod.: ±1.2KHz，Fmod.: 1KHz, Output level:1mV.

3. Squelch Volume set to minimum position, volume control set to around middle position.

4. Adjust IFT L20 for maximum audio output and minimum distortion at the distortion meter. ( distortion less than 5%).

5. Set volume control to maximum position, audio output power shall be more than 3 Watts.

6. UUT set to AM mode CH19，output of RF signal generator connect to TP2. Audio dummy load connect to EXT.

Speaker. (@8Ω load)

Model No: M760 Plus

Customer: INTEK Rev No: A

7. Set RF S.S.G Freq.: 10.695MHz，Mod.: 60%，Fmod.: 1KHz, Output level:1mV.

8. Squelch Volume set to minimum position, volume control set to around middle position.

9. Adjust IFT L5 for maximum audio output and minimum distortion at the distortion meter. ( distortion less than 5%).

10. Set volume control to maximum position, audio output power shall be more than 3 Watts.

4.2.2 Sensitivity Adjust:

1. RX RF bandwidth alignment: Apply Spectrum analyzer ’s Track Gen. Output connect to the UUT antenna terminal and input connect to the UUT TP3 (Q26 Emitter), center frequency set 27MHz, span set 30MHz, adjust IFT L4, L21 & L22 refer to attached table curve, then short TP3 & TP4.

2. UUT set to FM mode CH22，output of RF signal generator connect to TP5 (Antenna).

3. Set RF S.S.G Freq.: 27.225MHz，Mod.: ±1.2KHz，Fmod.: 1KHz, Output level:0.5uV.

4. Adjust the volume control for 2V output on distortion meter read.

5. Adjust L2 & L3 for more than 12dB at SINAD meter.

6. Repeat as needed. Check all channels sensitivity must met the D.T.S. specifications.

7. UUT set to AM mode CH22，output of RF signal generator connect to TP5 (Antenna).

8. Set RF S.S.G Freq.: 27.185MHz，Mod.: 60%，Fmod.: 1KHz, Output level:0.5uV.

9. Adjust the volume control for 2V output on distortion m eter read.

10. Adjust L2 & L3 for more than 12dB at SINAD meter.

11. Repeat as needed. Check all channels sensitivity must met the D.T.S. specifications.

4.2.3 T- Squelch Sensitivity Adjust:

1. UUT set to AM CH22，output of RF signal generator to the antenna input terminal.

2. Set RF S.S.G Freq.: 27.225MHz，Mod.: 60%，Fmod.: 1KHz, Output level: -47dBm.

3. Volume control and Squelch control set to maximum position，(Full C.W)

4. Adjust the RV5 to mute the speaker, then turn the RF S.S.G. output level to –47dBm.

5. Slowly turn RV5 to a position that the audio output on the speaker just appears from no output. Turn the RF S.S.G.

output level to -57dBm, the audio must be off from the speaker.

Auto Squelch Adjust:

6. UUT set to AM CH22，output of RF signal generator to the antenna input terminal.

7. Set RF S.S.G Freq.: 27.225MHz，Mod.: 60%，Fmod.: 1KHz, Output level: -104dBm.

8. Squelch volume control set to minimum and Off position (Full C.C.W).

9. Adjust the RV7 to mute the speaker, Slowly turn RV7 to a position that the audio output on the speaker just appears

from no output. Tu rn the RF S.S.G. output level to -107dBm, the audio must be off from the speaker.

4.2.4 RX Signal Meter Display Adjust: (For M-760 Only)

1. UUT set to AM CH22，output of RF signal generator to antenna input terminal. RF Gain volume at maximum. Power

switch turn on.

Model No: M760 Plus

Customer: INTEK Rev No: A

2. Turn the RF S.S.G output for 100uV without modulation.

3. Adjust RV6 for 9 characters displayed at the RX signal strength of the LCD.

4. Turn the RF S.S.G level output increase 30dB, the RX signal strength should up to +30 position.

4.2.5 Maximum S/N Detector & ANL detection:

1. UUT set to FM CH22，output of RF signal generator to antenna input terminal. RF Gain set to maximum, Squelch set to minimum, compander set off. (M-150 W/O Compander)

2. Set RF S.S.G Freq.: 27.225MHz，Mod.: ±1.2KHz，Fmod.: 1KHz, Output level: 1mV.

3. The Vo lume control turn to 0.5 watts audio output for reference A dB.

4. Then off the Modulation, here the audio output for reference B dB. A-B for S/N ≥ 35dB.

5. Compander set to On, repeat above item 3 and 4, A-B for S/N ≥ 50dB. (M-760 only)

6. UUT set to AM CH22, set RF S.S.G Mod. for 60%. Compander set Off. Repeat above item 3 and 4, A-B for S/N ≥

35dB; Compander set to On, repeat above item 3 and 4, A-B for S/N ≥ 50dB. (M-760 only)

7. UUT set to AM CH22, set RF S.S.G mod for 30%. RF level set 5.0uV. ESP set off. RF Gain set to maximum, Squelch

set to minimum. ANL set off, Noise generater (pulse 1us; width 100ms; output level 1.0Vrms) set to on and connect to the antenna socket with network combinator.

8. Set audio output level for 0.8Vrms for 0dB reference, RF S.S.G MOD. turn off, set ANL to ON, the audio output

should be drop 6dB or below.

4.3 TX Section Alignment.

4.3.1 TX output power and Frequency Alignment:

1. UUT set to FM EU CH19，Antenna connect to the RF power-meter input terminal.

2. Set UUT to TX mode, adjust the IFT L8 and L9 for TX power output maximum, and then adjust the RV4 check the

output TX power for 4.0W.

3. Set UUT turn to AM mode, check the TX power output for 0.7 to 1.3W.

4. Change to channel to UK band “U40” (27.99125MHz), Adjust the trimmer capacitor CT1 to 27.99125MHz ± 50Hz

on frequency counter. The UUT turn to EU CH19, check the TX carrier frequency should 27.185000 +/- 300Hz.

5. TX harmonics adjust and checking, turn to FM CH19, adjust L24 for 2

harmonic -36dBm below.

4.3.2 TX Signal Meter Indicator Alignment.

1. UUT set to AM CH19，input of power-meter to antenna input terminal.

2. Set UUT to TX mode, adjust the RV2 for “4” characters displayed at the TX signal strength of the LCD display.

4.3.3 TX modulation Deviation Alignment:

Model No: M760 Plus

Customer: INTEK Rev No: A

1. UUT set to FM I2 CH19, input of power-meter to antenna input terminal. Input of MIC socket to the audio frequency

signal generator output terminal. Mic Gain set to maximum. Compander set to Off.

2. Set audio frequency signal generator @ FREQ.: 1000Hz Output level: 50mVrms. Note: Should be add one

10uF capacitor in series between the AF signal O/P and UUT input.

3. Set UUT to TX mode, adjust RV1 for 1.6KHz deviation on modulation meter.

4. Decrease the AF output level. Check the 1.2KHz deviation modulation sensitivity should be between 8 -15 mV;

Compander set On, Check the 1.2KHz deviation modulation sensitivity should be between 3-8 mV.

5. Turn the AF output level for 1.2KHz deviation on modulation meter, check the modulation distortion must be less than

5.0% on the audio distortion meter for Compander On and Off..

6. Set UUT to AM mode; Set audio frequency signal generator @ FREQ.: 1000Hz Output level: 50mVrms.

7. Set UUT to TX mode, adjust RV3 for 90% deviation on modulation meter.

8. Decrease the AF output level. Check the 50% deviation modulation sensitivity should be between 8-15 mV;

Compander set On, Check the 50% deviation modulation sensitivity should be between 3-8 mV.

9. Turn the AF output level for 60% deviation on modulation meter, check the modulation distortion must be less than

5.0% on the audio distortion meter for Compander On and Off..

4.3.4 PA audio output checking:

1. The UUT enter PA mode after long press the “ANL” key, Volume set maximum position for M-150, and the MIC gain set maximum position for M-760. 1KHz audio input.

2. Turn to TX mode, the PA output must meet the DTS.

5.0 TEST MODE DESCRIPTION，Model Selection and International Band Select:

1. For M-760, Press both keys of “ANL” & “Scan” synchronously, then turn on the DC power enter test mode. Press

the “ENG” key for Software version checking, press the Channel “Down” key for LCD segments scanning checking.

2. For M-150, Press both keys of “ANL” & “DN” synchronously, then turn on the DC power enter test mode. Press the

“ENG” key for Software version checking, press the Channel “Down” key for LED segments scanning checking.

3. RX & TX parameter test: Press the “channel up” key can select Germany CH41 (26.565MHz), CH19(27.185MHz),

EU CH22(27.225MHz) and UK CHU40(27.99125MHz), PO CH01A and RU CH40L.

4. EEPROM control for VCO alignment for Channel RU 14D, RU 15D, RU 21G and RU 22G.

5. VCO Alignment Channel: PO band CH01A(25.610MHz) ---- Low channel; RU band channel CH40L(30.105MHz)

---- High channel.

6. Model selection and European band and International band selection.

Model select: M-150 R146 = N/A and R145 = 10K; M-760 R146 = 47K and R145 = N/A. (CPU PIN64 pull high for M-150; CPU PIN64 pull low for M-760) International Band select: “IB” pad open for European band only, International band disable; “IB” PAD shorting that the International band enable and the European band enable also. (CPU pin 21 pull high for International Band)

Model No: M760 Plus

Customer: INTEK Rev No: A

7. BAND SELECTION:

M-150: 1) switch ON radio while pressing the UP key

2) display will show the current band ID code (blinking)

3) select band using the UP or DN keys

4) shortly press the DN key to confirm

5) display will show the selected band ID code for 2-3 seconds, then it will show the channel number

M-760:

5) display will show the selected band ID code for 2-3 seconds, then it will show the

6.0 Factory Setting of Band for Shipment

FACTORY SETTING

All radios must be shipped from factory set as follows : BAND SETTING : EUROPEAN BANDS ONLY

RADIO SWITCH ON : CE BAND

1) switch ON radio while pressing the EMG key

2) display will show the current band ID code (blinking)

3) select band using the UP or DN keys

4) shortly press the EMG key to confirm channel number

Step Setting

Frequency adjustment MIC : Receive Volume : optional Squelch :

optional CH selector : 19 EU CH9 : off

VCO Voltage adjustment MIC : Receive Volume : optional Squelch :

optional CH selector : 1A CH9 : OFF

Connection Adjuster Adjust for

Frequency counter to dummy load

CT1 27.185MHz±300Hz

(Figure 1).

Connect DC voltmeter between R97, C112and

L17 1V at RX.

GND. (Figure 2).

Model No: M760 Plus

Customer: INTEK Rev No: A

Schematic Diagram

VCO CIRCUIT DIAGRAM

Model No: M760 Plus

Customer: INTEK Rev No: A

COMPANDOR CIRCUIT DIAGRAM

PLL CIRCUIT BLOCK DIAGRAM

1. INTRODUCTION

The frequencies for transmitter and receiver first local frequencies are all derived from a single 4.0 MHz crystal by means of a phase locked loop. The first local oscillator frequencies are 26.965 MHz (CH 1) to

27.405MHz (CH 40) for EU and 27.60125 MHz (CH 1) to 27.99125 MHz (CH 40) for UK . The second local frequency is fixed at 10.240 MHz to generate second IF 455 KHz.

The VCO operating frequency for the receiver is 37.660 MHz (CH 1) to 37.560 MHz (CH 40) as the first local oscillator, injected through the buffer AMP Q411 into the first fed balanced mixer Q2 and Q3.

2. BASIC SYNTHESIZER SCHEME

The crystal frequency (4.000 MHz) is divided by 800 times to make 5 KHz which is fed to one side of the phase detector. The VCO output is divided by a programmable divider, and fed to other side of the phase detector of IC4. The feedback loop is closed by passing the phase detector output through an active low pass filter and using the output to control the VCO frequency through varicap diode D402,D403

Under locked conditions, both of phase detector input signal must be indential at 5 KHz. The VCO frequency is then given by:

FVCO / N = 0.005 MHz or FVCO = 0.005 x N MHz

Since “N” is an integer, the VCO frequency can be stepped up with 5 KHz increments. By suitable choice of “N” the desired output frequency can be obtained.

N FVCO N FVCO

Transmit 5393 26.965 5481 27.405

Receive 7532 37.660 7620 38.100

Channel 1 Channel 40

FUNCTION

Transmit 5520.25 27.60125 5598.25 27.99125

Receive 7659.2 38.296 7737.25 38.68625

Since all frequencies are obtained from the crystal controlled PLL oscillator, all outputs are coherent with the crystal oscillator frequency and maintaining the same percentage accuracy.

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