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Fisher FM-200-B Muting Switch

notdigital

notdigital

AK Subscriber
Subscriber
Not to interrupt an ongoing thread on another unit, I thought I'd start a separate thread on a switch issue I'm having. Specifically, I determined that the switch behind the MUTING pot is defective. Consequently, the indicator light is always on.

Here is the switch as repaired to stock condition:

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Below is the switch as wired in my unit with what I have available as a replacement, i.e. the SPST black switch on the right. Can it be wired to replace the original switch. It seems like I can move the 330k resistor to share the lug with one black wire; if so, how would I accommodate the bare grounding wire? Tap it to the case? Possible? Not possible? :scratch2: :scratch2:
 

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Not -- In the FM-200B, the muting control switch (as you know) is a double switch. One side of the switch merely turns on and off the indicator lamp. That's it. The lamp is not controlled by any internal circuitry -- just the switch to let you know that the muting circuits are engaged. The other side of the switch controls the B+ to the muting oscillator. When switched off, there is no power applied to the muting oscillator, making it impossible for the circuit to mute the last limiter stage at all.

Short of getting the correct switch, you could make your SPST switch work, but it would take some modifications to do so. Basically it would involve developing a low current 12 volt DC power source, and then have your SPST switch activate a DPDT 12 volt relay, which would active the Fisher circuits.

On the other hand, the new switch was not terribly expensive, and available from Mark Oppat.

Good luck with your project!

Dave
 
dcgillespie said:
On the other hand, the new switch was not terribly expensive, and available from Mark Oppat.


Dave
Click to expand...

I have one that I purchased for one of those "just in case" moments. I'm not sure I want to give it up to the tuner.

I have a bunch of the single throws. Maybe it's about time I perform micro surgery.....

Thanks Dave.
 
Anatomy of a Toasted Switch

Necessity dictated that I delve into what I had been loathe to do, that is, try to repair a toasted switch. For those who would be up to working through the frustration of manipulating tiny pieces, the pictures below will either give you pause or reason to take up the challenge.

It's pretty straightforward, tiny elements aside. Simply lift the spring from the center lock washer, slide the washer to free it and remove; remove the phenolic base to expose the toasted contacts; clean out the guts; replace the burnt contact and reassemble.

This toasted switch is the one that I removed from my X-202-B:

http://www.audiokarma.org/forums/showpost.php?p=8101302&postcount=1

Now onto taking out the tuner switch and replacing it.....
 

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So I take it you sacrificed a SPST switch to get a good contact to repair the defective one?

Dave
 
Yup Dave. Now I only have 5 left :D

And thanks Fred. But guess what? I'm keeping my day job!!!!!!
 

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