Author Topic: 206 Amp Backwards Capacitors?  (Read 212 times)

Offline theseacowexists

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206 Amp Backwards Capacitors?
« on: February 20, 2020, 07:17:48 AM »
I'm working on a Wurlitzer 206 for a friend. A previous owner had already chopped it and modded it for an aux output and tremolo control, and those all appear to have been installed and are work correctly. The amp is quite noisy, so I replaced all the e-caps, and that helped a bit, but I've noticed something after looking at the diagrams. Is it possible that the original caps could have been installed backwards? I'm certain the three large filter caps are correct, but it's the small ones I am wondering about. There are three diagrams in the service manual, one undated, one dated June 1971, one dated June 1973. The polarity of all the small caps does not seem to match between all three diagrams. The actual board I'm working on is stamped Jan 4 1973, so it would make sense to me that the June 1971 diagram is the one I should be going off - although the actual caps don't seem to match that diagram, either!

I'm also going to replace some of the more brittle looking resistors, as I know that's helped on my Pianets. Also, C-12 (not an e-cap) appears to have been clipped out at some point - might as well put a new one in.

Offline theseacowexists

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Re: 206 Amp Backwards Capacitors?
« Reply #1 on: February 20, 2020, 07:18:36 AM »
The three diagrams and a shot of the board

Offline Tim Hodges

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Re: 206 Amp Backwards Capacitors?
« Reply #2 on: February 20, 2020, 07:44:06 AM »
So the main power supply caps are fine (those 3 large Mallory's)

Are you talking about the axial electrolytics on the left hand side? Are the negative leads going to ground? I have some photos of a later 1974 board but not all are clear.

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Offline theseacowexists

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Re: 206 Amp Backwards Capacitors?
« Reply #3 on: February 20, 2020, 08:28:15 AM »
Yes, the ones on the left are the ones I'm talking about. So all of the negatives should be going to ground then?

Offline Tim Hodges

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Re: 206 Amp Backwards Capacitors?
« Reply #4 on: February 20, 2020, 02:42:18 PM »
Can you take a photo of the underside of your board?
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Offline theseacowexists

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Re: 206 Amp Backwards Capacitors?
« Reply #5 on: February 20, 2020, 02:52:28 PM »
Here ya go!

Offline DocWurly

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Re: 206 Amp Backwards Capacitors?
« Reply #6 on: February 21, 2020, 04:24:30 PM »
The 1973 diagram has a lot of stupid errors in it, yet is the last and most up-to-date diagram.  Basically, when they rotated the amp in the graphic so that it faced the way a user would ACTUALLY look at the thing, they neglected to rotate the polarity of a lot of items in it.  The ones I am aware of are the Diodes:  D2 through D5.  I didn't know about the capacitors, but it would not amaze me.

There is a version of the amp from around 1972 that seems to be a transition from the 1971 to the 1973 amp.  So there are really 5 different periods of 200 amps.  At least.  and that doesn't take into account all the classroom variants.

I am about to do exactly what you are doing.  I have a hunch that the high wattage resistors on these boards dry out, start getting super-hot, and make a lot of noise.  R-14 gets BURNING hot on these things.  That may also be a sign that something else is failing, so we'll see what happens next.
« Last Edit: February 21, 2020, 04:29:02 PM by DocWurly »

Offline theseacowexists

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Re: 206 Amp Backwards Capacitors?
« Reply #7 on: February 25, 2020, 02:51:12 PM »
I ended up leaving the caps alone, as everything was working well enough. I did replace the missing C-12 cap. The high wattage resistors were all replaced, that seems to have helped tame some of the amp noise. The piano is back with my friend, but I did offer to replace all of the resistors if it's still too noisy for her taste. So far, she seems pleased with it.