Superstar 3600 feedback on FM RX and SSB TX/RX.

[Chevin]

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).

[Rick]

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.

[Chevin]

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).

[zodiac]

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