After about 40 years of messing around with electronics and super-8 film, I used contact cleaner for the first time recently. I’d like to talk about the experience and discuss where to go from here.

The background here is in our daily lives, we almost never have trouble with the oxides on switch contacts. When we walk up to a 115V or 240V light switch and engage power, there is enough voltage across any oxide film that builds up that the film bursts and then enough current pours through the breach to burn that opening wide-open.

If this was the world of low voltage and low power, you would flip on the room lights and they’d be dim, or even dark. If you then flipped the switch a bunch of times often the lights would brighten. (-and so, we are grateful for decently forceful house current!)

-now let’s talk about the world of audio electronics:

These signals are quite often well under 10 Volts and can be down in the milliwatt or even microwatt range power-wise. There’s no bursting, and no burning where oxide films are concerned. The oxide film holds its ground and almost all of the signal voltage stays there where it’s of no use: there’s little to nothing to amplify and as a result the audio in the speakers is a whisper at best!

They COULD use gold-plated switch contacts but (…you know!).

My first exposure to this was a nice-looking Elmo ST-800 on the used equipment shelves at a local camera shop about 20 years ago. I got it home and there was no sound. I suppose I really should have brought it back to the shop, but this is not my nature: either I fix it or destroy it trying! (This really irritated people until I became better at it!)

I figured I’d divide and conquer: plug in headphones and see if the signal got that far. I got sound in the phones. Where it got pretty interesting is when I pulled that plug out and found that the audio worked through the speaker as well. Our culprit here was the cutoff switch built into the headphone jack. Like a great many switches, it self-cleans if you use it. Before I plugged phones in that jack, it was just status-quo where that oxide film was concerned.
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This same machine lost sound again several times in coming years. Usually it very gradually happened so that I found myself up at full volume setting but with wimpy results in the speakers. The usual suspect was the red recording key, and relief came from working it like a telegraph key. This is where what I call “The Switch Trick” was born (at least for me...I get the feeling people doing projector repair knew it when I was still wrestling with Long Division!). It’s worked for years when someone comes on here and they say they have no sound: roughly half the time this brings the sound back.

I used it to bribe someone for information once. He was selling a machine with new belts but no sound. I offered him The Switch Trick in exchange for where he bought the belts. That day, everybody won!

The Switch Trick finally hit an iceberg in the form of another ST-800:

Elmo Archaeology: Reviving a 40 year old ST-800

This one came from a camera shop too, but not from the used shelf. Some customer had never picked it up when it was brand new and it was still in the shop when they cleaned it out after it went out of business.

It was shocking in its mechanical virginity: no wear on the guides, bits and pieces the average owner discarded pretty early were still installed: basically brand-new! It was also a wonderful opportunity to see what it was like to get a new Elmo long before I could afford one. (NOT that I didn’t want one!)

This one also turned out to be the Champion of switch oxide buildup. No amount of Switch-Trickery could keep the sound on for more than a week and last Fall I had to take this machine off-line (-it kind’a hurt!)

Something had to be done!

I knew it was the recording switch, because with a great deal of exercise, this at least temporarily brought the sound back. My choices were clean, replace or bypass.

I have a dead sound board, so I took a look. (NOTE: Both of these pictures were shot on the dead board: hence the dust!)
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ST-800 Recording Key: The part you usually DON'T see

This is a weird switch: it is designed to be operated by tension and returned to resting position by a spring. It just may be a unique Elmo fabricated part: I did a lot of web searches and it didn’t even come close. Now we were down to just clean or bypass.

This machine still has lock washers under the cover screws and a ty-wrap holding the speaker connector together, just as installed in Japan all those years ago. As close to “mint” as possible, this machine IS “mint”. I may never record a track with this machine, but soldering jumpers on the back of the board and losing original functionality just didn’t sit well with me. Bypass wasn’t completely out, but it was now a last resort.

-so now we are down to just “clean”! (-if at all possible)

I went to Home Depot and got this potential can of magic:
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Back at the house I removed the rear guide, the control knob and the screws holding that panel in place. I flipped the board down as close to upside-down as possible. This switch is a plastic armature sliding inside an aluminum tube. When it is fully up, the armature and the tube form a tiny pocket. When all this becomes upside-down, a drop of contact cleaner would pool in there and drain between the armature and the inner tube wall: hopefully reaching those same oxidized contacts that brought us all here today.
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Record Switch upside-down with the armature withdrawn:
The contact cleaner is on target and ready to spritz!

This was a family operation: my wife and I as a team-effort held the flashlight, depressed the record switch and aimed the tube from the contact cleaner into that pocket and held the pieces of projector properly oriented with Earth’s gravitational field (It’s the only one we have!). I spritzed, I waited, then I worked the recording switch and repeated: three, maybe five times. (My son was still at college: could’a used him that night!)

While I was at it, I aimed the tube inside audio jacks and gave them a spritz too, and anything else I could get to with a movable contact.

The can said “allow product to dry thoroughly before applying power” and used disturbing words like “flammable”. They didn’t give a timeframe, so I decided I was in no hurry: I let it sit until well into the next day.

After I fully re-assembled, I gave it a try. Me being me, I forgot I turned the volume control fully down while I was working, so until I figured this out there was no sound! “Oh, CRAP!....(Oh!)”. Once I set the control right, the sound came back big-time and about two months later, it’s still going strong: literally just like new.

I’ll have to say: I’m impressed!

-but, let’s remember: this was a first experience for me. You may count me as a newbie where contact cleaner is concerned. I think I can take it for granted that access to the contacts isn’t always this easy. What happens with other switches?

For example, I’ve had a couple of cases where the snap switches operated by the control knobs are obviously oxidized: the transport is slow until I work that switch a number of times.

I’ve replaced these switches and it’s not exactly the kind of activity that draws people into film collecting. Maybe contact cleaner is a good plan “A” before I basically ruin a Saturday afternoon. Is there any place on the body of these switches I can spritz some cleaner and have it reliably reach those contacts?

Does anybody else have some useful experiences using contact cleaner? I’d like to know about them!