Ok, Back to the radio...
No Receive.
Each question will be followed by a NO and YES answer.
Is there hash in the speaker?
NO Run you finger over the audio chip or do the metal probe on pin 4. If still no noise check pin 10 for 13.10 volts. You can check rest of the pins and make sure the voltages are as followed:
pin 1- 13.7 pin 2- 6.63 pin 5- 1.14 pin 9-6.86 pin 10-13.10 Rest of the pins should be at zero. For some reason you vave the same voltage on many pins look for a bad ground. If you have 13 volts (supply voltage) on 3 or more pins most likly the chip is bad. If there is no sound at all and all the above is good then make sure the mic is wired correctly. If ok then check ffrom the output of the chip towards the speaker. work your way towards the audio transformer and check C46. This is a coupling cap. Now work you way through the PA switch and the external speaker jack and then to the speaker. Make sure you check all caps along the way. These cap isolate DC from the audio line.
YES
Is the Receive indicator light on?
NO The receive LED is fed from R113. Check the 8 volt receive supply regulator TR23. Check C119. It is underated and fails often. Replace it with a higher voltage cap. Check the zener diode D22. It has a high failuer rate also. If D22 or C119 fails this will remove bias from TR23. That is all the voltage rail for the Receive supply.
YES
Does pin 11 of IC 1 have 5 volts?
NO Check D19. There should be 5 volts on it. If R124 is warm then most likely C112 has shorted. If the voltage is low check C97.
YES
Is the 10.240 oscilator working?
NO There are a lot of components in this circuit. We know the voltages are ok because of the checks that got us this far. Either the crystal is bad or there is a bad solder joint. D6 is a varactor diode. This is a diode capacitor combination. If the internal capacitance changes the circuit will not oscilate.
YES
More later
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RT.
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