Black Russian Big Muff fried out

[fuzzdoge]

A friend of mine fried her Russian by accidentally using a power supply with wayy too many volts. 40v dc roughly I think.

I've replaced the electrolytic, assuming this was the only thing fried. Good news is that it sounds like a muff again. Bad news is that now the pots are all scratchy and not working correctly at all. Get them in the right spot and they work but are extremely touchy and not gigable at all.

Before I go and replace the pots could it be something else? Can too much voltage fry the pots?

[GibsonGM]

Measure for DC on those pots, try to find out where it is coming from.  That is what makes the scratch (barring physical destruction).  My first guess is of course going to be that you missed a coupling cap, it is leaking DC thru....

Yes, pots can happily die from exceeding their power rating - depends how long your friend had 40V on them and what they were set at at the time.   Set at 90k, you'd have microamps and 100ths of Watts.    Set low, tho, and you can easily burn a pot out.

Check your caps again, look for DC on both sides of each one using 9V or less.  I think the damage is already done, so don't worry about creating "more"...you can center the pots first to make yourself feel better if you like.   Go thru the circuit in an orderly way, and you will probably find the issue pretty quickly...

If all else is cool, and no DC on the pots, then I would consider replacing them, as long as I've assured myself nothing else is 'going on'.

[anotherjim]

Weird. I would not have thought the DC blocking caps to the pots would be damaged as they are supposed to be film types. Has it been got at/modified  with electrolytic types for those caps? The only one electrolytic in the whole thing should be on the power supply input.
Could be that electrolyte from the fried cap vaporized and got in the pots? Give them a squirt of your favourite electro -lubey type stuff if you can get it inside them.

[GibsonGM]

Weird. I would not have thought the DC blocking caps to the pots would be damaged as they are supposed to be film types. Has it been got at/modified  with electrolytic types for those caps? The only one electrolytic in the whole thing should be on the power supply input.
Could be that electrolyte from the fried cap vaporized and got in the pots? Give them a squirt of your favourite electro -lubey type stuff if you can get it inside them.

Another good thought, Jim.  I did think the coupling caps would be too small to be electro, and are typically rated much higher...hmm....maybe the resistive surface in the pots DID get toasted.     Worth a try if some cleaner is on hand! 

[fuzzdoge]

Yeah the electrolytic had properly exploded - inside out almost! There was debris everywhere.

She only had it on for a second - smoke and a pop and then she pulled the supply out.

No mods previously - except that I had replaced the pots for her a few months ago, because the originals were on their way out.

I can't find anything wrong with the circuit so I'll replace the pots and see how it goes.

Thanks for your help!   

[fuzzdoge]

update:

Replaced the electrolytic cap and the 3 pots and its fixed.


Can't believe it fried all 3!

[intripped]

As Anotherjim said, probably the explosion of the electrolytics has dirtied the pots.
If you want to keep it original I think that you could restore them with an accurate cleaning (opening them and using some soft paper and contact-cleaner)