Author Topic: Volume control issue  (Read 899 times)

TC Chris

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Volume control issue
« on: December 19, 2015, 04:33:24 PM »
I've just posted an inquiry on the solid-state Maggie section but I'll ask here too.  Problem is that part of the number is missing from the paper label but it's a solid-state Magnavox from the 1970s or so. 

The problem is a non-functioning volume control.  I used some DeOxit F5 "Faderlube" on it because it was really dirty, noisy, and intermittent.  After that, the left channel worked fine but the right channel goes from no noise at all to a little bit of sound to quite loud--three discrete steps as you rotate the pot.  I was fairly generous with the DeOxit but that right channel is still not functioning.

I poked around to see if maybe there was a bad solder joint where the pot joined the circuit board but nothing changed.

Any suggestions or ideas?

Chris Campbell

Harbourmaster

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Re: Volume control issue
« Reply #1 on: December 21, 2015, 06:54:44 PM »
Flush the pot again... try a different solvent like WD-40 or CRC-QD Electronic Cleaner. Once you have it working you can put a few drops of Faderlube in it.
-- Aloha, Ken

No Console Left Behind!

TC Chris

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Re: Volume control issue
« Reply #2 on: December 21, 2015, 08:21:20 PM »
I have another theory.  The Faderlube fixed the left channel's noisiness.  The right channel isn't noisy--it just goes abruptly from very faint loudness to loud functioning.  It doesn't crackle or drop out.

I looked at the downloads for solid-state preamp schematics.  None matched this device, which was later, but I noticed that they all had taps on the volume pots for loudness control.  Some had two taps.  If a loudness tap's associated capacitors were shorted, it would cause the effect I'm hearing-very little sound as you rotate the pot about halfway, then sudden (and too loud) effectiveness of the pot after you pass the shorted tap

I really need a schematic and chassis layout diagram of this device to diagnose it properly.  It also needs to be extracted from the console, which involves a rat's nest of wiring with the @#?*$!!! molex connectors.  Here's the data I could find on th device:  The paper label is missing the first letter of the unit no.-- what is left reads  _G6654PN01.  Inside on the back cover there's a connection diagram with two additional numbers:  W-75002 and R-34403BA.  It's approx. 1977--the receiver portion resembles the device in the 1977 catalog.


Chris Campbell

xaenon

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Re: Volume control issue
« Reply #3 on: July 26, 2016, 05:35:33 PM »
What you describe is almost exactly what's happening with my 1975-ish Magnavox.   Did you ever get this resolved?

TC Chris

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Re: Volume control issue
« Reply #4 on: July 26, 2016, 09:58:14 PM »
Not yet.  It's my colleague's device, and she lives down the alley from me with a husband, kids, and two nasty small white dogs.  Now it's summer and all indoor projects are deferred until fall, and perhaps until the nasty small dogs die of general nastiness.  When I first looked at it, I was having trouble removing all the stubborn Molex connectors that keep it snared in the console.  I am thinking that in its current condition, it's not much use, so maybe I'll use more muscle on the connectors and get it free so I can take it home and test it without the small dogs yapping in the background and trying to eat me.  Meanwhile, I'm sailing and when it rains, trying to get the '61 Chevy to start.

Chris Campbell