I know someone out there must of worked on one of these rigs at one time or another.. Currently I am working on one that I bought new years ago and I brought it out of storage and decided to restore it's operation ...
First, the FM on this rig never worked the way it should have, always low audio level on receive but I never cared for that anyways back then and never gave it any thought.. But I decided now to look into it. It appears on the RF board, the one on the bottom behaves like it has leakages in the circuit.. Why I say this is because I am getting enough voltage on the emitter of Q39 which also has a DIODE (D109) connecting to the FM decoder chip to partially squelch out the audio...
According to the print I shouold be getting near 0 volts here in RX mode but I get around 3 volts which is enough to forward bias D109 and mute the FM audio.
I looked at every component that is connected to that rail, things like the TX switch that supplies 8 volts to that rail down to all the tracks to disables the RX RF buffers etc..
I disconnectec diode after diode looking for leakage and found none but thbere absolutely voltage getting there with no sign of where its coming from... So I noticed that if I loaded the line down with a 1k resistor it all works great. Btw, there does not appear to be any shunting R to common as it is now? Bad design maybe but normally you have a pull down R, I can't locate one anywhere in that circuit.
SO I notice when I disconnect diodes to the various paths on the board this leakage voltage was reducing itself..
I've come to a conclusion that the fiber board has come partially conductive over time and due to the multiple paths for possible leaks this all adds up and since I see no pull down R in the circuit any where, I put in a 1K and not it seems to work...
Does all this make any sense at all ?