GP350 Problem

[arlojanis]

I have a UHF GP350 that has a funny problem. Power on beep is OK. I can read and write it OK. It does not receive a signal. There is background noise if I press the volume set button. When I press and hold transmitt, there is a very quick blink of the red LED and no transmitted signal. Both 16.8 and 7.9 crystals are OK. What are more things to check?

[Al]

Sounds like a synthesizer problem - common to both rx and tx. Have you looked at the rx injection at the first mixer to verify the frequency and level? The lock detect line on pin 20 of the uP should be at +5V if the synth is in lock. Do not overlook the possibility of a faulty channel select switch, SW401. It's BCD outputs to the uP are on pins 34(1), 36(2), 37(4), and 38(8), active low.

[arlojanis]

I have tried injecting 455 khz and 45.1 mhz and heard nothing. I tried injecting 1 khz tone to the volume control and heard nothing. I scoped the volume control and saw nothing while generating a signal. The monitor led will come on after pressing button. The busy LED never comes on. I am thinking about subbing the channel selector switch.