Fisher 400 NO FM stereo : ( FM mono works great

[bowtieman427]

Hello all, just restored my Fisher 400 and for some reason the left channel in FM Stereo mode is very scratchy, staticy, not getting the full frequeny respomce bandwidth, and low db intensity. When I play a CD left and right channel sound great and equal. FM Mono sounds great and equal on both channels.
Tunning eye working and equal on both sides.
ANY IDEAS OF WHAT IS WRONG, WHERE THE PROBLEM MAYBE OR WHAT TO CHECK.

Thanks in advance
Jim

 

[NOSValves]

Did you change any caps in the MPX section?

First thing I would do is the simple approach. Clean and reseat all the tubes/sockets in the MPX section.

Craig

 

[bowtieman427]

This is an early 400..I have replaced C214, C221, C222, and C210. I have also removed the tubes cleaned them again and well as a shot of deoxit in the the sockets. Result was the same : (

 

[BrassTeacher]

With the unit on, try wiggling the tubes in the multiplexer, one at a time, and see if you get any noise. If you do, it may be new tube socket time, and you have my condolences if that turns out to be the case. OTOH, at least it wouldn't be a tube tester socket!

 

[Whaleman]

Swap the 12AX7 tubes on the MPX around and see if the problems follows the tubes, then swap the IF tubes around. Make sure to mark their original locations, I had the same problem, swapping the tubes seem to cure it.

 

[NOSValves]

I'd inspect your work on the MPX section. Maybe a cold solder joint or a lead shorting out......It's really tight in there.

 

[bowtieman427]

Thanks all got it fixed it was a bad soldier job on my part. Sounds great
Jim