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Need help diagnosing broken gain knob on a Crown PS-200

cmb3366

cmb3366

Well-Known Member
Need help, odd substance on transformer on a Crown PS-200

Well, I got my Crown PS-200 in from e-bay today, beautiful, but its got a major issue, the seller has been informed about a potential return, but I figured I would ask some more experienced people aboutt possible easy fixes first.

I am having trouble with the left channel gain knob on my PS-200. When I got it, the right knob matched its clicks with the markings, but the left knob did not. I removed the left knob to make sure it was on right, but apparantly there is only one way to install it. I put it back on, still way off the markings. So I went to pull it off again, and now, this time the shaft pulls out with it, till it hits a stop. Now I cant get the shaft to return so it turns the volume. Is this how the knobs are set (is there a trick to putting it back together), or is the volume control just plain broken? Thanks a bunch.
 
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No clue on a fix, but that might be something you can get a parital refund from the seller to offset the costs of repair...

Just have to figure out how to do the repair....I'm guessing a swap of the controls would be in order, but I'm not sure.
 
Well, I grew a pair, popped the cover off, and took a look. No biggie, just a loose screw, bingo working pot, and everything matches up. However, a look at the insides raised another question.

The transformer, and the clothcovered wires leasing out are covered in a tarry substance, everything else inside is clean as a babys behind, aside from the usual dust. Does anybody know what went on here?


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From the pictures it looks like the amp and transformer were super-heated at some point. I can see that the back plastic cover of the transformer is deformed and, if I had to guess, I'd say the black stuff is melted "potting" material that flowed out of the transformer when it was hot.
 
Thats exactly what I was thinking. Is this nessecarily a problem (something to wrangle with the seller about), or just cosmetic, and nothing that will affect sound?
 
It seems to me that a lot of transformers have something similar -- I assume its some sort of tar that is used to immobilize and insulate the windings in the transformer. I don't think that there are plastic parts deformed as suggested above -- looks more like twisted wires to me.
I think its more important to see if it works properly than to focus on how things look -- looks are important, and may be a clue to past use and so important, but they aren't why you bought the amp.
 
Well, I appreciate all the helpful input, it helped a bunch. I took your advice Nat, buttoned her up, and threw it in the rack. The amp is a playing fool, so far so good, and it doesent run hot in the slightest. If sound is any indicator, I'd say this amp is A-ok.


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Transformer is OK.

What you are looking at is tar potting on part of the transformer leads nearest the body, this is normal and not a over heating situation.

There must be a situation where they dip the transformer body in tar or other potting compound and they do cover some of the leads coming out of it, as I work on these amps. and have seen many working units with this "look" to the transformers.

As for the broken pot, there is a small "D" shaped stem on the back end of the shaft, it is normally "peened over" at the rear of a small plastic disk inside the body of the control.

Because of the shape, the shaft may have been pushed back in 180 degrees wrong, making the front knob point in the wrong direction, if the front shaft is round, just push the shaft back in and loosen the knob screw and re-position the knob.

If the shaft won't stay in, try a little epoxy on the very end and see if it holds, the only problem is the disk may have cracked in two pieces.

Hope this helps.

Mark T.:music:
 
Thanks for the reply Mark.

I got the pot/knob working 100% again, it was just a loose connecting screw that was letting the lefthand knob 'freewheel', I tightened it, and it works perfect once again, and the markings match up perfectly.

As far as the tar covered pot, I've done some scrounging for interior pics of these amps, and they all seem to have it, so like you said, I think it was a result of factory assembly, not abuse. The amp plays beautifully, Stays COOL, looks awesome, matches my SL-2, and suits my needs. I couldent be happier with it.

I know its blasphemy, but I'm considering buying another to replace my McIntosh... time will tell.
 
Glad to help, now for my bill...

Glad to help with your questions, now you can ship me that McIntosh you won't be using!:banana:

Have fun!:yes:

Mark T.:music:
 
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