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I have a Fisher FM50-B that is dropping out one channel once fully warmed. As I'm starting to go thru it a schematic would really help. Anyone have the schematic they could share?Many thanks,
- Gary
Follow Ups:
I have a 500B that did the same thing. i would turn it off, and the channel would return.Since the 500B has similar if not the same tuner section and MUX (is it a WX board?) as the 50B, here is what happened w/ mine.
When i would put the selector in mono, both channels would play fine, but in stereo, the right channel would drop, and this is after I did the upgrades to that section as well, IE caps and resistors upgrades.
What the problem was there is a loopstick coil in the mux section that had a cold solder joint on it! After I resoldered, this solved the problem.
I hope this is the case w/ you too, I heard everything from the tubes to the diode packages in this section too!
Good luck,
Jeff -I also suspected a cold solder joint, and hearing your experience was reassuring.
I reflowed the mpx section and the output section. I also replaced all of the electrolytics under the chassis and the output coupling caps.
With about 20 hours of listening the shotgun approach appears to have worked!
The Fisher FM-50b is a pretty nice sounding tuner btw - not as sensitive as my FM200B or R200's but every bit as musical sounding on a good signal.
Many thanks!
Gary,Your welcome, glad it works now. Probably a very warm sounding tuner. I'm in a suburb of Chicago and there is a station WXRT 93.1 that is classic/album rock and the DJ's voices that come out of my 500B are just too lifelike to describe!
BTW, was it in the MUX section, ie did both channels work in mono mode only to drop when stereo? If so your problem was most likely in the MUX section.
One other note, my 500B is haunting when it comes to pulling in stations, even in my basement w/ no external antenna, I can pick up a Kenosha, Wi station loud and clear. Might want to check the alignment out.
Glad to help,
Jeff -Unfortunately, other than the simple alignment used by Dynaco FM3's I have no experience with FM tuner alignment. I do have basic instruments (scope, 5mhz function generator, HP334a distortion meter and frequency counter etc) but no sweep generator. Any good references or basic instructions for getting started?
Gary,Unfortunately I did not have to align any of my units, however I have "tweaked" the front end using the tuning eye or meters, whichever the tuner has and w/ success turing ever slightly and carefully getting the front end (the tuner gang adjustment screws, or the rf section as in fisher tuners) up to par.
I was suggested this by others who do these restorations. I DO NOT touch the IF or Mux sections. If I would ever need it done, i would contact paul at BizzyBee since he is only a 1/2 hour drive from me.
http://www.2baudio.com/However for both of my 400 and 500B, the service manuals do have the alignment procedures.
Hope this helps,
I have a 400 with the same problem, I will give it a looksee this weekend; thank you for the tip.
... do you know if it's in Sams? If so, my father probably has the Sams. Sams has an on-line index (I'll bet you knew that) :-)Season's greetings!
I'd looked in the past, but must have botched the search. It does show up as being available!I have the Sams for the FM-50, but don't have a copy of the FM50-B version. Apparently it is a schematic only - any chance your dad might have #889 FISHER FM50B?
I used to get them at the public library in Boston, but that isn't practical since my move.
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