The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Can anyone help with my SS3900 PCB #EPT360014B PLL #MC145106P. The problem I have is feedback on FM RX and the same on SSB TX/RX. I have replaced the Mic Op-Amp IC4 and most of the caps around the Mic Op-Amp but this has made any difference to the problem.

Bret (AKA Chevin).

Check RX/TX switch transistors TR36.37 and 38 plus D77, It sounds like TR36 is leaking, check base to emitter junction. Let us know how you get on.

Rick.

Check the transistor like Rick suggested and found tr36 with 920 ohms between base to emitter. I could not find a 2SB525 so I have used a BC640 which is 1 amp 80 volts. I think this transistor will be ok. Rick can you let me know if this is ok to use this transistor.

I got this Superstar 3900 from a guy which told me it had been to 4 different rig doctors and none could fix-it. It just shows that Rick certainly knows is stuff.

Bret (AKA Chevin).

The BC640 will do just fine but it's pinout is E.C.B. The 2SB525 is B.C.E.