Fisher 800T No Sound Except Through Tape

[mikiekimi]

Anyone have a block diagram for the Fisher 800T? Getting ready to tear into one that has good sound on Tape In, but nada on AM/FM/Phono/Aux (neither headphone jacks nor speaker terminals). Reverb plugs are in place. Looking over the SM it appears Tape bypasses the preamp and possibly the control amp. Seeking confirmation.

 

[larryderouin]

500-tx is essentially the same as an 800-T. 500TX is Single Voltage, 800-T is multi voltage. Use a 500-TX manual. Tape monitor comes in just after the Reverb jacks. Make sure the jumpers are in correctly. These ARE NOT Preamp out/ AMP in jumpers. CLEAN the Source selector switch (actually do ALL of them on the front panel) with DeOxit. Spritz and exercise all of them 50 times. Then test again.

 

[mikiekimi]

Thanks Larry, I was hoping that the basic control cleaning would solve it, but no luck. The jumpers are in correctly. I have SMs for both (I've worked a few 500Ts in the past). Nada on the block diagram in either 500T manual I have. The folks that own this said it was working fine - then suddenly no noise. They listen to it on AM/FM/Phono/Aux.

 

[larryderouin]

Pull jumpers and heat shrink across the bend, leaving the end legs bare. The bend is such that if they are pushed in too far, they short against the outer ground shell of the jack. Heatshrinking the bend and pushing in until they grab will keep from shorting signal. Clean the jumper pins and the jacks. Tighten jacks as needed. that's the only thing I can think of that would kill the signals from the preamp as everything goes thru it and S-1 (source selector). Tape mon has it's own equalization pre.

 

[mikiekimi]

Thanks.

They were already heat shrinked. I cleaned them and re-positioned them to be sure they weren't shorting the signal.

According to the owner (original owner BTW - pretty cool...couple in their 80s), the receiver sound dropped while they were listening to a CD via AUX. They turned it on/off and it came back for a few minutes, then dropped completely and hasn't made a peep since. I just happened to test TAPE since I know sometimes tape inputs sit outside of the preamp/tone controls.

I'll need to trace a signal and see what board it's dying at...hope it warms up soon so my garage 'bench' get above freezing and I can spend some time on it.

 

[Sterling245]

I had this issue on one of my 800ts and if I remember right the issue was a bad regulator on the power supply board. I'll get you more info tomorrow when I have the service manual in front of me!

 

[fred soop]

If both channels are out, then it is probably not switch contacts or reverb jumpers. More likely a problem in the preamp power supply. That's the one thing common to both channels.

 

[Sterling245]

I had this issue on one of my 800ts and if I remember right the issue was a bad regulator on the power supply board. I'll get you more info tomorrow when I have the service manual in front of me!

I looked at the service manual and I believe it was Q972 that was bad. (RCA TR-1001).

 

[mikiekimi]

I looked at the service manual and I believe it was Q972 that was bad. (RCA TR-1001).

I think you're onto something. PS Board 9EE should be +12 (it's +4.5) and 9DD should be +30 (it's +6.5).

Is there a modern sub for Q972? Looks like maybe an NTE 128...

 

[larryderouin]

A bit overkill but a KSA1220ay should work. I heard a month or two ago that NTE had gone out of business. Makes it harder to cross reference now. The KSA 1220 can be had at mouser for about $0.35 ea

 

[mikiekimi]

A bit overkill but a KSA1220ay should work. I heard a month or two ago that NTE had gone out of business. Makes it harder to cross reference now. The KSA 1220 can be had at mouser for about $0.35 ea

Pretty sure I have 1220s in the stash

 

[mikiekimi]

This community is just wonderful. You all undoubtedly saved me hours of tracking this down. Popped a 1220 in there and it fired right up

Can't thank you all enough!