Fisher CA-871 Receiver Intermittent

This unit has been a major pain.... the original symptom was the sound cutting out on both channels. It would run normally for a while and then cut out, or sometimes it would power on with no sound (relay clicks on, final preamp and output stages are fine). Tapping the volume up or down control causes it to come back on. Without a service manual, I could only take guesses. I replaced two IC's (TC9177P and TC9185P, volume control) on the control board, but no change. I replaced a third IC (AN4046 equiv) and again no change. In desperation, I tried replacing every last transistor and filter capacitor on that board, and checked the value of every last resistor. STILL no change. Never one to give up easily, I'm considering ordering a service manual. But if there's a possibility of logic problems or other expensive/tricky/impossible repairs needed, I don't want to waste $20 on a manual. Do you think this is a simple problem or will it require too much time and money to make it worthwhile? Or is it possible that the replacment IC's were defective? Thanks for any advice.

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Reply to
Chris F.
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I've got the same system and have had the same problem numerous times. The slider volume control has been the culprit on mine. Once I gave it a very vigorous cleaning it worked great for a while. Every once in a while I've got to do it again. In fact it is starting to act up again now so I guess I should dig into it. I ordered the service manual way back when I first bought the system so if you have any questions about any specific part I can give you the reference from the manual.

Cheers, Lawrence

Reply to
lmcclaf

I was going to say... how about just cleaning the controls?

Mark Z.

Reply to
Mark D. Zacharias

Oops sorry, my mistake. I misread the model number. My unit is a CA-271.

Lawrence

Reply to
lmcclaf

Check the speaker relay-s . Have the thing going and when it quits stick a screwdriver across the relay contact pins on the bottom of the board or ``whack`` the relay .

Reply to
Ken G.

Nope, not it. I would have found that quite easily. As I said in my first post the main output stage is fine (you can inject a signal), the trouble seems to be in the volume control section. Maybe this thing just isn't worth bothering with.......

Reply to
Chris F.

That TC1985P chip uses leg 3 as an inhibit or some such thing for when you turn the system off to retain a memory of where the volume was set or something like that. If you measure what you have at that leg when things are fine and then measure again when it kicks out you might find something funny being felt there which is throwing the volume out of whack. Tapping the volume controls would then override what the "memory" is trying to do so that might be why it is coming back when you hit the buttons. Grasping at straws here but doesn't cost nothing for a look.

Cheers, Lawrence

Reply to
lmcclaf

"Chris F." wrote in news:AHeXg.4049$cz.58002 @ursa-nb00s0.nbnet.nb.ca:

CLEAN THE DANG VOLUME CONTROL!!!

Reply to
Jim Land

It's DIGITAL NOT A SLIDER POT!!

Reply to
Chris F.

yes and no. It's a cheapie control. Typically they're using conductive and non conductive 'spokes' with rotary sliders running across them to generate the digital signal, usually a quadrature square wave. If the sliders or the conductive spokes get dirty/intermittent you get extra glitches which will give you a screwed up count or no contact which will give you no count at all, hence intermittent control or no volume. An awful lot of all-in-one small stereo's suffer from this. The bad news is the pot is probably sealed so good luck getting cleaner into it. And if it is a all-in-one small stereo good luck getting at the control!

tomh

Reply to
tomh

Perhaps I should be more clear: there are two buttons - one for volume up, and the other for volume down. There are no pots involved whatsoever, it is entirely logic-controlled.

Reply to
Chris F.

ahhh, excuse me, well check the buttons themselves, to see if they are closing. Pulling up to +V or down to ground. In an older unit they'll probably be directly connected to the chip doing the volume control. Or to a chip that puts out a data stream to the volume control chip. If it's a newer unit they may be scanned by a 'jungle chip', and you'll need a scope to check the waveform at the switch. If tapping or wrapping on the chassis brings the volume back or makes it go away, I'd also get out the magnifier and look for bad solder joints and breaks. If it is a newer unit with lots of IC's and you don't mind spending the time, do a lot of resoldering around the volume control IC and elsewhere. Ya might get lucky...

Reply to
tomh

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