How to Fix Those Flaky/Intermittent Plastic Switches

[Anderton]

...you know, like the ones on the Alesis HR-16, MMT-8, and a slew of other products. They use conductive plastic that sits above traces on a circuit board. When you push the switch down, the plastic goes across the circuit board traces, and closes the circuit.

 

The problem is that "time happens." For whatever reason, the contacts become dirty, or oxidized, or whatever it does they do that makes your life difficult. So here's how to fix the issue. All you need is 90% isopropyl alcohol (you don't want anything that leaves a residue), some Q-Tips, and whatever tools you need to disassemble the device that needs fixing. These images show how to do this technique with an Alesis MMT-8, and all it needs is a small Phillips head screwdriver. However, the same principle applies to a lot of other gear: figure out how to get to the surface of the switch's conductive plastic and the circuit board in which it comes with contact. It's amazing how responsive those cheap little switches become after you clean them!

 

Open up the case. With the MMT-8 and HR-16, it's four small screws in the corner.

 

 

Then remove the connectors so you can remove the circuit board.

 

 

The circuit board mounts against the switches. Unscrew the circuit board so you can get at the traces that make contact with the switches, as well as the switches themselves.

 

 

Once the circuit board is free, wipe off the switch contacts.

 

 

Then wipe off the circuit board traces.

 

 

And there you have it - I hope you find this useful.

 

 

[zeronyne]

I think Sunshine Jones eventually found that there is a limit to this refurbishment.

 

[Anderton]

But he scraped the contacts!! ARGH...circuit board traces are very thin, and scraping will not be consistent. Pencil lead just flakes off shortly after you apply it. Alcohol and Q-Tips are the answer, because they don't degrade the contact - they just clean them.

 

Now, he was talking about using them live and taking them all over the place. No inexpensive plastic gear will hold up to that for years on end. But in a studio context, the procedure I described really works. Breakage and "heavy hitters" notwithstanding, you can keep the HR-16 and MMT-8 going pretty much forever.

 

 

[Piktor]

Craig, I finally got around to checking out this forum. I"m glad that I did. I will be back more often.

 

Thank you for the cleaning information. A couple years ago I set an article from the July 1989 issue of Keyboard magazine where Myron Malhon had written a short article similar to the tip that you gave us here, but he did not include the helpful pictures. I"ve been meaning to get around to fixing my old flakey HR-16, even if just to use it to trigger some drum samples from a Motif rack ES.

 

Mahon preceded the alcohol swapping with another step. He rubbed a clean rubber ink/pencil eraser over the contacts first and then used alcohol. My techy friend did the same thing with my old Multimoog key contacts and had great success. Do you think that extra step is not necessary, or might it be advisable to do that for more severe problems?

[Mike Rivers]

Mahon preceded the alcohol swapping with another step. He rubbed a clean rubber ink/pencil eraser over the contacts first and then used alcohol. My techy friend did the same thing with my old Multimoog key contacts and had great success. Do you think that extra step is not necessary, or might it be advisable to do that for more severe problems?

 

The contacts on your drum machine are, as Craig showed, just circuit board traces, and it looks like they're just tin plated. That's pretty soft stuff, but it protects the copper underneath from tarnishing. Erasers are abrasive, and you don't want to erase the tin off the copper. So I'd avoid it.

 

Keyboard contacts, on the other hand, and edgeboard connectors, too, are often gold plated. That's a little tougher than tin and can benefit from a light "erasing." You don't want to use an ink eraser, though. Those are too abrasive. A "Pink Pearl" drafting eraser used to be the recommended tool, but now that drawing boards have gone the way of the wind-up Victrola, you may need to get a vintage eraser.

[Piktor]

Thanks for the advice Mike.ð

[Anderton]

Craig, I finally got around to checking out this forum. I"m glad that I did. I will be back more often.

 

Welcome!! Please feel free to start topics...and tell your friends. The more, the merrier

 

As to the cleaning process itself, empirically, I used only alcohol on the HR-16 and MMT-8, and the switches work as good as new (if not better, actually). I should have done the cleaning years ago instead of just hitting the buttons harder!

 

Mike's right about keyboard contacts, however for edge connectors, remember that gold is one of the most malleable substances around. With something like cards that go into a motherboard slot, I find that just lifting up a bit and pushing back in wipes the contacts sufficiently to give me another five years.

 

One more contact thing: I couldn't figure out why my OB-8 wasn't working. Upon closer inspection, the metals used for the chip pins and sockets were different. Small crystalline structures had grown between the two, and were causing shorts to other pins. It kind of freaked me out to realize non-organic things were growing inside my OB-8...