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Proton D940 Restoration

Vintage Solid State - AudioKarma.org Home Audio Stereo Discussion Forums - www.audiokarma.org
I had an earlier thread with a couple pics but decided to make a new one detailing the work I'm doing on this "had it since new" restoration. It's mainly just getting a recap, cleaning, relube, regrease, etc. But, I am finding some places on the board where heat is a definite part of the equation. So, some resistors, diodes and other parts are getting a little more attention... i.e. replaced if I have the parts in stock. At this point I'm not planning on replacing the main PS filter caps, but I can change my mind if I want to.

I have done a little work in the past on it...removing the tuner's ceramic filters and installing sockets and narrower ones to achieve better selectivity, but haven't yet tracked down an issue with the tuner display. Frequency shows odd digits, and the search function doesn't really work anymore. So, as I started the teardown I've been looking at solder joints etc. Lo and behold, the center conductor for the 75ohm antenna connection was broken, so perhaps that's the issue. I suppose it could also be the 7.2MHz crystal feeding the oscillator, so I'll keep that in mind.

I have discovered a variable resistor that is NOT referenced for any adjustments, so I'm wondering if any know what it's for? It's in the volume circuit and is labelled as VR801. (VR601/602 are on another part of the board and are for setting the amp BIAS).

Caps are Panasonic FM, FC and ECQ (possibly), Nichicon PW, KL, others as needed, and some Kemet film caps.

Here's some innards:

Tuner Board

Preamp section (also shows VR801 at end of ribbon cable)

Power supply

More coming.
Date: Aug 31, 2015   


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