Advice for reviving an old Boss pedal

[Jefe]

I've got a 1986 Boss HM-2 that I haven't used in a long, loooong time. I figured I should sell it. I plugged it in today to make sure it still works OK, and guess what? It doesn't. The LED is dead, which I can probably replace no problem. But the sound is wrong... I know these things sounded bad to begin with, but something is wrong. Way too raspy/fuzzy, and the volume is going up and down a bit. I pulled up some youtube videos to refresh my memory about how it's supposed to sound, and there's definitely something wrong with mine.

So, any advice on where to start? Should I spray the pots with pot cleaner? Are there any known issues with these, as in, are there any components I should check first?

It's entirely possible that a bonehead friend of mine damaged it decades ago when he borrowed it. His name way Ray, and he was an idiot. Knowing him, he may have plugged the wrong power supply in to it. I seem to remember trying the pedal some 20 years ago and thinking "hmmm, something sounds wrong", then putting it back on the shelf and forgetting about it.

Any advice, tips or tricks would be greatly appreciated.

[m-Kresol]

Hmm. The LED being dead sounds like a problem with the power/ground rails. Probably check for continuity between the two first. If you do have a schematic for the effect you can of course use an audio probe to poke around. It could just be misbiased though.
On another matter: I was told to never ever use pot cleaner. Apparently it's no good and and will just delay the ultimate failure of the pot...

[the3secondrule]

Before you replace anything: does it have a sticker specifying which powersupply to use?

If it says to used an ACA adaptor, there is a resistor and diode you'll need to jumper to work properly off standard 9v supplies. Google ACA to PSA mods (I'd I link but I'm posting from my phone) 

[the3secondrule]

Otherwise, look out for leaky electros.
They'll usually have corroded/stained spots on the solder side of the board

[Jefe]

Thanks for the replies guys.

I've heard mixed things about pot cleaner. One thing I do know is that WD-40 is NOT pot cleaner. I don't know why anyone would use that. I've got a can of the standard Radio Shack stuff. It helps with pots that are scratchy & have been sitting a long time.

I did make an audio probe years ago, but have never used it. Hope I can find it, lol. I'll look up the schematic.

It has a sticker stating ACA adapter, so I made sure to plug it in to one of the ACA outputs on my Voodoo Lab Pedal Power 2 Plus.

Good call on the leaky electros, that hadn't crossed my mind.

Thanks again!

[JohnL]

I had the same problem with mine. Worked sort of, sounded like a fuzz and not in a good way. Replaced all the electros and some of the other caps that had seem to have leaked and it now works fine.

[Jefe]

Really JohnL?! Very interesting, good info, thank you! What made you think some of the other caps (the non-electros) had leaked? Could you visibly see something wrong with them?

[JohnL]

At least one of the 47n (I think that size) had goo coming out of it so I replace all of them and a few others that looked suspicious.