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Analogue radio repairs

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PostPosted: Thu Nov 10, 2016 8:52 am    Post subject: Analogue radio repairs Reply with quote

Radios for hard to fix radios
Fault. Doesn't turn On (Dead radio)
1/Check Fuses
2/Resolder On / Off switch, carefully without creating solder bridges to
SMD caps.
3/ Dead battery.
4/ 7.9 Mhz crystal module near the CPU is faulty
5/ Check 5volts on pin 4 of U411.If found to be faulty must replaced with the same as you remove, G5 reg. Can not be replaced with R5 reg (reg. for the CPU)

FaultNo TX Audio or low TX Audio
1/ Replace internal flex cable.
2/ Check for bad soldering on C457 caused by dropping
3/ Resolder and retention accessories socket
4/ replace internal mic. First check to see if the is a DC on TX across the internal Mic

FaultNot responding to sub-tones.
1/ check for bad soldering on C412 and C413

Fault. Cant change Rxer volume.
1/ Bad soldering on the volume control.

Fault. Distorted Rx Audio.
1/ Iron fillings in speaker grill
2/ Bad speaker

Fault. No TX/Rxer Audio
1/ O/C Accessory socket, Resolder and retention
2/ Replace the flex internal speaker/mic cable
3/ No Rx audio, check the out put of the Audio Amp ( IC 409 )

FaultTransmit audio squeals
1/ Resolder VCO Tank circuits. (L258 - L259)
2/ check out C249 either resolder or replace

FaultNo TX or Rx but the lights are on
1/ O/C soldering on the Channel Switch
2/ Check 5volts on pin 4 of U411 (reg. for the CPU). Must be G5 regulator. R5 regs generally work better.

FaultTX LED flashes but no output power
1/ Change U411 (CPU regulator)

Fault. Weak Rxer.
1/ Change Both I.F. crystal filters
2/ Read the radio and then check TX frequency, maybe off frequency, retune the radio using software

2/ if you read this radio with version 2 , program with version 2 . If you read with version 3 you program with version 3. NEVER use version 4. ie , program the radio with the same software you read it with

FaultLow range
1/ Replace the antenna Pin with new type
2/ If new type already installed, retention and clean contacts.
3/ If current consumption is normal change Pin diodes.
4 /If current drain is low, PA module is faulty
5/ Check if the radio is on frequency, it must me within 100Hz to the programmed frequency

GP328 Multibay chargers.. no output voltage
1/ opto coupler faulty, can be changed with 4N35 but you need to reverse the new opto 180 degrees cause theLED and the transistor is the other sides
Fault red LED flashes for no reason
1/ locate faulty transistor near the lower mounting screw in a white square

GP328 Rxer Audio sounds tinnie and low
1/ Adjust via software the mic gain.internal mic gain and external have to be the same

Max 638. CPU not turning on and the radio turning off after on for only about 2 seconds.
1/ Connect pins 4 and pin 10 to make the CPU turn on and the radio to work. Numbered just like the
2/ to put this into test mode either short the data pin on the mic socket to earth or plug in a RIB box and do not turn it on and them turn the radio on. It should be in test mode.
3 never use software version 4. This is for the USA market and will delete some software

Shinwa Radios..To adjust the squelch control there is a POT next to a 4011 I.C. on the solder side of the PCB. This is the squelch level control

GP328/338.. No Rxer Audio
1/ check speaker
2/ Check Flex cable connections to PCB socket
3/ if there is a GP300 Speaker Mic adaptor, does it work without it.
If yes, change the adaptor.

Fault..No speaker/mic operation but internal mic working
1/ please check R435 and C404 and C433 for physical damage

Fault.Running radio on Power supply and the RED L.E.D. flashes to show low battery
1/ replace temp sensor cause the temp sensor shuts down the PCIC chip

Fault.Radio is dead battery Ok
1/ Check for 5 volts on either pin 13 or 17, if not there replace the PCIC (U201)
2/ If no voltages around the temp. Sensor (CR105) change it. This is used to sense the temp. Of the battery when charging.

Fault . Hetrodyning
1/ The GP328/338 radios when tuned above 500 Mhz are able to receive an image 10 Mhz above and below the oridinal frequancy. To fix this problem alter the tuned cct in the Ant. Coupling ccts

Fault.Low or No Tx power
1/ If current consumption is normal change Pin diodes.
2/ Look for current changes on the power transistor and test PN Junction for short circuit.
3/ Damaged flex cable.
4/ If current drain is low change or Nil change PA transistor

Fault. No TX Audio
1/ Bad or damaged components, L400 and R421.
2/ Damaged flex cable.
3/ faulty internal Mic. (Must have about 2.5volts Dc across it on TX)

Fault.radios beeps when the PTT is pressed and again when released
1/ CPU software (Not the software you program) is corrupted, change the microprocessor.
2/ Change Flash RAM, due to missing firmware
3/ Replace ASVIC chip, not transferring data from the cpu to the rest of the radio

FaultTurns on and off intermittently.
1/ Cracked solder joints on the on off switch.
2/ Battery connection terminal block either not soldered well, damaged or loose
3/ faulty PCIC chip or temp sensor

Fault.No Rx Audio but the Key pad Audio ok.
1/ Check for Audio on pin 14 or 15 of U420.
2/ Check speaker and flex cable for Open circuits
3/ check the caps to ground on the volume pot.

FaultPoor Rxer, distorted audio
1/ Change ASFIC chip (U404)

Fault Intermittent pausing RX Audio
1/ The ASFIC Chip is the cause of subtone related Audio trouble. Over modulated RX Audio can distort the subtone decoding and cause this problem too.

FaultAudio amp oscillating when at full volume
1/ missing RF shield over crystal filters

Mobile radios.
Faults. Blows fuses.
1/ Check reverse protection diode
2/ Check Voltage regs

Faults. Poor LCD.
Check and replace the elastomer

Faults.Pin 4 not go to 12 VDC
1/ Check Q802 Located on the bottom of the RF PCB near the back of the radio

Maxon mobiles
1 / to change the TX Audio: adjust VR4

kenwood TK370
fault drifting frequency
1/ replace the reference oscillator crystal with another part number L77-1726-05 and serous resistor R58 with patr numberRK73-GB1J-223J

Tait 2000II
1/ No Rx Audio.earth Speaker earth ,one pin on acc. Socket to get Audio on internal speaker

Special notes !!!!
When hands free set is connected
Radios on 412 to 415 Mhz when transmitting cause Samsung
CDMA Phones to dial out (last number redial)
When programming the XTS2500,shift /TAB /Enter will get the radio to go out of band

The flex cables used in the 838s can be used in HT1000 and simular trunking radios

27 Mhz CB radios.. Weak TX, (100's of Milli-watts out the antenna)
Faulty PA reg, Rxer not affected

Most PA transistors can be replaced with 2SC2166 with 27 Mhz CBs

The pin diodes in the GP300 can also be used in the 338and the 328

The computer cable connections to the HUB orange/mate and orange, blue/mate and blue, green/mate and green/mate a
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