Intek M-790 Service Manual

Name: Intek M-790
Brand: Intek
SKU: 7761826
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Model No: 3391 Drawring No: Customer :

Model No:

M-790 Plus

Rev,Date:

M-790 Plus

Service Manual

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Model No: 3391 Drawring No: Customer :

Title M-790 Plus

Rev,Date:

Table of Contents

Page

Specifications 3 Test and Alignment Procedure 4 Block Diagram 14 Schematic Diagram 15 Printed Circuit Board 25 Channel Frequency Charts 26 Parts List 38 Semiconductor Voltage Chart 48 Semiconductor Lead Assignment and Block Diagram 55 Exploded View Parts List 58 Exploded View 60

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Title M-790 Plus

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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

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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.

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THEORY OF OPERATIONS

TRANSMITTER

A. RF Amplification

The output of double AMP Q301 is fed through tuning IFT L301 and L302 to the base of pre driver AMP Q302. The output is then supplied through tuning circuit L303 to RF driver AMP Q303. The output of Q303 is supplied with tuning circuit L304 and C317,C315,C21 and goes to the base of final RF AMP Q304. The output of Q304 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 Q304 and antenna, 4-stage “PHI” network L308, C324, C1, C327, L311, C337, C333, L312, C328, C334, C338, L313 serves as a spurious radiation suppressor . This network also serves to match the impedance between TX power AMP Q304 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. RV1 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 RV1 to make 4 w indication of RF power meter.

The tuning is adjusted so that the actual power is from 3.8 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. RV401 limits the incoming modulation audio levels to inhibit over modulation. While reading the modulation factor on the modulation analyzing equipment, adjust RV401 shall not exceed +-1.8 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 D203 and corresponding ALC circuit limits the modulation shall not exceed +/-80% adjust RV201 +/-80% modulation under 1.0 KHz AF 60% mod plus 20 dB of audio signal.

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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 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 Q105,Q106 mixes the incoming RF signal to generate first IF signal. Mixed signals were filtered with the XF101 (10.695 MHz) crystal filter and other tuning circuits. Output signal of mixer is filtered with CF101 (455 KHz ceramic filter). The 455 KHz signal from the 2 quadrature detector loop L104. Then we can see the recovered audio signals on Pin 11 for FM of IC102. With the amplitude of recovered signals, Q112 serves as an audio amplifier. For AM signal Will be pass filter CF101 and induced to Q116, Q117 respective and detected to voice signal by D111.

IF filter was amplified and limits internaly. After amplification the signals fed the

IF section and 2nd IF section.

TROUBLESHOOTING HINTS

Symptom

• Defective power switch VR102.

Unit does not work at all

No output from speaker at all

No noise on speaker

• Blown fuse.

• Broken DC power cord.

• Defective IC101.

• Defective external speaker jack.

• Poor connection on microphone connector

• Defective push switch on microphone.

• Defective internal speaker.

• Defective VR102, IC103 other components.

• Measure all the voltage of IC102 with voltage

chart

• Defective squelch circuit components (RV102, VR1, IC102)

Probable Cause Remedy

• Replace

• Repair or replace

• Replace

• Replace the defective

components.

• Replace

Squelch does not work

• Defective VR1, RV2, IC2.

• Replace the defective

components.

• Re-adjust

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No modulation

• Defective microphone.

• Poor audio output and defective modulation

microphone amplifier components (IC103).

• Defective microphone connector components.

• Defective ALC circuit D413, D414.

• 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 D5.D3

• Defective IC101.

• Defective RV101.RV202

• Defective RED wire fuse.

• Defective IC101, Q414.

• Defective IC101, SW105. • Replace

• Defective EMG SW.

• Defective IC101.

• Replace

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ALIGNMENT PROCEDURE

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 (Figure 1).

Connect DC voltmeter between R406, C411 and GND. (Figure 2).

CT201

L501 1V at TX.

27.185MHz±300Hz

Figure 1 Figure 2

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TRANSMITTER SECTION

Test Equipment Required

• RF power meter (RF SSVM) • DC power supply (13.2 volt, 3 amp)

• 50 ohms dummy load (non-inductive) • Spectrum analyzer

• RF attenuator (50 ohms non-inductive) • Frequency counter

• Oscilloscope • Coupler

• Audio generator

ALIGNMENT PROCEDURE

Step Setting

RF power stage MIC : Transmit Volume : optional Squelch : optional

CH : selector : 19 CH9 : OFF

Second harmonic check MIC : Transmit Volume : optional Squelch : optional CH : selector : 19 CH9 : OFF

Connection Adjuster Adjust for

Connect dummy load and RF power meter to the EXT-ANT jack on the set (Figure 3).

Connect RF power meter With dummy load to spectrum analyzer through coupler /-40 dB Attenuator to EXT-ANT jack on the set (Figure 4).

L301 L302 L303

At no modulation,

Maximum indication on the power meter (4 watts). If indication is not in 4 watts range, adjust L301, L302, L303.

compare the level o fundamental frequency to the level of harmonic frequency. Suppression of the

harmonic frequency level must be lower than –60 dB. Check for the other channels.

Frequency check MIC : Transmit Volume : optional Squelch : optional

CH : selector : 19 CH9 : OFF

Connect dummy load and frequency counter though coupler to RF powermeter. Connect RF powermeter to EXT-ANT jack on the set (Figure 5).

CT201 Be sure that the

indication of the transmitter frequency is 27.185MHz±300Hz on the frequency counter.

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TX power level adjustment Volume : optional Squelch : optional

CH : selector : 1 CH9 : OFF

Connect dummy load and oscilloscope through Coupler to RF powermeter connect audio generator to microphone jack (Figure 6).

RV202 Adjust until the 5

appears on the channel display LCD.

bar

Figure 3

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Figure 4

RECEIVER SECTION

Test Equipment Required

• RF Signal generator (RFSG)

• SSVM

• Distortion meter

• DC power supply

ALIGNMENT PROCEDURE

Step Setting

Audio output adjustment MIC : Receive Volume : Fully clockwise Squelch: Turn to- Counter clockwise CH selector : 19 RF gain : Fully clockwise

CH9 : OFF RFSG:27.185 MHz,1kHZ 1µV , 1.2 K Dev.

Connect RF signal generator to EXT-ANT jack. Connect SSVM and distortion meter with 8 ohm dummy load (Figure 7).

Connection Adjuster Adjust for

L101 L102 L103 L104 L106 L401 L402 L403

Maximum indication on SSVM. Reduce output from RFSG until the audio output becomes about 500mW (2V).

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Squelch adjustment MIC : Receive Volume : 50mW (2V) Squelch : Clockwise

CH selector : 19 RFSG:27.185MHz, 1kHZ 1mV, 1.2K DEV.

Connect RF signal generator to EXT-ANT Jack. Connect SSVM and distortion meter to EXT speaker jack with 8 ohm dummy load (Figure 7).

RV1 Adjust until the audio

output appears.

RF signal meter adjustment MIC : Receive Volume : 500mW (2V) Squelch : Fully counter

Clockwise RFSG: 27.185 MHz, 1kHZ, 1µV, 1.2K Dev.

Connect RF signal generator to EXT-ANT Jack. Connect SSVM and distortion meter to EXT speaker jack with 8 ohm dummy load (Figure 7).

RV101 Adjust until the 3

LED on the S/RF meter lights up.

Figure 5

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Figure 6

Figure 7

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INTEK M-790 ESP

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PLL CIRCUIT BLOCK DIAGRAM

1. INTRODUCTION

The frequencies for transmitter and receiver first local frequencies are all derived from a single 4.5 MHz crystal by means of a phase locked loop. The first local oscillator frequencies are 16.270 MHz (CH 1) to

16.710 MHz (CH 40) for EU and 16.90625 MHz (CH 1) to 17.29625 MHz (CH 40) for UK . The second local frequency is fixed at 10.240 MHz to generate second IF 455 KHz. During transmit, The VCO of the PLL operates 13.4825 MHz (CH 1) to 13.7025 MHz (CH 40) for EU ,13.800625 MHz (CH 1) to

13.995625 MHz (CH 40) for UK the VCO frequency gose to the double circuit Q301,L301,L302 which doubles the frequency to generate 26.965 MHz (CH 1) to 27.405 MHz (CH 40) for EU and 27.60125 MHz (CH 1) to 27.99125 MHz (CH 40) for UK

13.4825 MHz (CH 1) EU 26.965 MHz (CH 1)

13.7025 MHz (CH 40) EU 27.405 MHz (CH 40)

13.800625 MHz (CH 1) UK 27.60125 MHz (CH 1)

13.995625 MHz (CH 40) UK 27.99125 MHz (CH 40)

The VCO operating frequency for the receiver is 16.270,16.90625 MHz (CH 1) to 16.710,17.29625 MHz (CH 40) as the first local oscillator, injected through the buffer AMP Q506 into the first fed balanced mixer Q107,Q108

Q 408

VCO

Q 301

Doubler

To Transmitter

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2. BASIC SYNTHESIZER SCHEME

The crystal frequency (4.500 MHz) is divided by 1800 times to make 2.5 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 Pin 75 of IC101. 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 D503,D504

Under locked conditions, both of phase detector input signal must be indential at 2.5 KHz. The VCO frequency is then given by:

FVCO / N = 0.0025 MHz or FVCO = 0.0025 x N MHz

Since “N” is an integer, the VCO frequency can be stepped up with 2.5 KHz increments. By suitable choice of “N” the desired output frequency can be obtained.

Channel 1 Channel 40

Function

N FVCO N FVCO

Transmit 5393 13.4825 5481 13.7025

Receive 6508 16.2700 6684 16.7100

Transmit 5520.25 13.800625 5598.25 13.995625

Receive 6762.50 16.90625 6918.5 17.29625

(SEE TABLE FOR OTHER CHANNELS)

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The VCO frequency goes to the double circuit, which doubles the incoming signals.

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Double output Frequency

Transmit _______

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.

CH 1, 13.4825 MHz CH 1, 13.800625 MHz

CH 40, 13.7025 MHz CH 40, 13.995625 MHz

26.965 MHz

27.60125 MHz

27.405 MHz

27.99125 MHz

INTERNAL BLOCK DIAGRAM

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DIVIDE RATIO, VCO RX/TX FREQUENCIES FOR EACH CHANNEL OF “EU”

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Channels

1 26.965 6508 16.27 5393 13.4825 2 26.975 6512 16.28 5395 13.4875 3 26.985 6516 16.29 5397 13.4925 4 27.005 6524 16.31 5401 13.5025 5 27.015 6528 16.32 5403 13.5075 6 27.025 6532 16.33 5405 13.5125 7 27.035 6536 16.34 5407 13.5175 8 27.055 6544 16.36 5411 13.5275

9 27.065 6548 16.37 5413 13.5325 10 27.075 6552 16.38 5415 13.5375 11 27.085 6505 16.39 5417 13.5425 12 27.105 6512 16.41 5421 13.5525 13 27.115 6516 16.42 5423 13.5575 14 27.125 6524 16.43 5425 13.5626 15 27.135 6528 16.44 5427 13.5675 16 27.155 6532 16.46 5431 13.5775 17 27.165 6536 16.47 5433 13.5825 18 27.175 6544 16.48 5435 13.5875 19 27.185 6548 16.49 5437 13.5925 20 27.205 6552 16.51 5441 13.6025 21 27.215 6608 16.52 5443 13.6075 22 27.225 6612 16.53 5445 13.6125 23 27.255 6624 16.56 5451 13.6275 24 27.235 6616 16.54 5447 13.6175 25 27.245 6620 16.55 5449 13.6225 26 27.265 6628 16.57 5453 13.6325 27 27.275 6632 16.58 5455 13.6375 28 27.285 6636 16.59 5457 14.6425 29 27.295 6640 16.60 5459 13.6475 30 27.305 6644 16.61 5461 13.6525 31 27.315 6648 16.62 5463 13.6575 32 27.325 6652 16.63 5465 13.6625 33 27.335 6656 16.64 5467 13.6675 34 27.345 6660 16.65 5469 13.6725 35 27.355 6664 16.66 5471 13.6775 36 27.365 6668 16.67 5473 13.6825

Frequencies

(MHz)

RX TX Frequencies MHz

Frequencies MHz

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37 27.375 6672 16.68 5475 13.6875 38 27.385 6676 16.69 5477 13.6925 39 27.395 6680 16.70 5479 13.6975 40 27.405 6684 16.71 5481 13.7025

DIVIDE RATIO, VCO RX/TX FREQUENCIES FOR EACH CHA NNEL OF “UK”

Channels

1 27.60125 6546.5 16.90625 5412.25 13.800625

2 27.61125 6766.5 16.91625 5522.25 13.805625

3 27.62125 6770.5 16.92625 5524.25 13.810625

4 27.63125 6774.5 16.93625 5526.25 13.815625

5 27.64125 6778.5 16.94625 5528.25 13.820625

6 27.65125 6782.5 16.95625 5530.25 13.825625

7 27.66125 6786.5 16.96625 5532.25 13.830625

8 27.67125 6790.5 16.67625 5534.25 13.835625

9 27.68125 6794.5 16.98625 5536.25 13.840625 10 27.69125 6798.5 16.99625 5538.25 13.845625 11 27.70125 6802.5 17.00625 5540.25 13.850625 12 27.71125 6806.5 17.01625 5542.25 13.855625 13 27.72125 6810.5 17.02625 5544.25 13.860625 14 27.73125 6814.5 17.03625 5546.25 13.865625 15 27.74125 6818.5 17.04625 5548.25 13.870625 16 27.75125 6822.5 17.05625 5550.25 13.875625 17 27.76125 6826.5 17.06625 5552.25 13.880625 18 27.77125 6830.5 17.07625 5554.25 13.885625 19 27.78125 6834.5 17.08625 5556.25 13.890625 20 27.79125 6838.5 17.09625 5558.25 13.895625 21 27.80125 6842.5 17.10625 5560.25 13.900625 22 27.81125 6846.5 17.11625 5562.25 13.905625 23 27.82125 6850.5 17.12625 5564.25 13.910625 24 27.83125 6854.5 17.13625 5566.25 13.915625 25 27.84125 6858.5 17.14625 5568.25 13.920625 26 27.85125 6861.5 17.15625 5570.25 13.925625 27 27.86125 6866.5 17.16625 5572.25 13.930625 28 27.87125 6870.5 17.17625 5574.25 13.935625 29 27.88125 6874.5 17.18625 5576.25 13.940625 30 27.89125 6878.5 17.19625 5578.25 13.945625

Frequencies

(MHz)

RX TX Frequencies MHz

Frequencies MHz

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