Test Equipment Anonymous

Thanks to a member of FB group "Old Tech Scopes" was shown a neat trick for getting deoxit into sealed or otherwise inaccessible pots. Candidate for this treatment is a Type 1A4 Four Channel Plug-in. These plug-in's have a notorious reputation for developing noisy vertical position pots that are completely sealed and to add to the issue the pots for channel 2 and 3 are inaccessible. First step is to remove the knobs. Position the plug-in upright. Then seal the outer ring of the pot. I used shrink tubing which fit perfectly. Then spray dexoit into the cavity and let it sit for at least an hour. The deoxit should eventually flow down the inner shafts. Reinstall the knobs.



Results? Much improved compared to previously but not perfect. These pots have a known issue for developing dead spots which no cleaner will fix. And it's a dual gang pot so forget about getting a replacement. But in it's current state usable. I suspect on other pots the results will be much better if not perfect. It's certainly worth a try.

That is a neat trick. Perhaps we ought to have a section with handy tips and tricks like that in it.

Pedant alert!
As you got the deoxit into them the pots are clearly not "completely sealed". Fully enclosed with no access maybe.

Robert.

Semantics. Are they hermetically sealed or considered "explosion proof"? No, far from it. I believe you work in the aviation industry therefore "completely sealed" would be held to that higher standard. So perhaps I should have said just "sealed", which they are considering the only way to get any deoxit in there is via the shafts of the pots.

Interesting.

I've also heard it suggested that pots can be submerged in IPA or IPA/acetone mixture. A slight vacuum would help. IPA is surprisingly cheap if you buy it by the 5litre bottle. Of course, once you've got the solvent in there, you have to get it back out again. It should evaporate and find its way out in time.

Isn't it desirable to have some sort of sympathetic lubricant, at least on the track?

There's Caig Faderlube. I haven't tried it.

Similar tactic I've used is to place the spray tube of a food-grade silicone spray can parallel to the shaft, then seal it with heat-shrink tubing around shaft and threads. Spray away, remove tube & tubing, then work the control.

You'll want to get some paper towel around the back of the control first if there's any chance of the spray dripping onto a Hi-Z or HV area.

mnem
*tssssssssst*

I've always been distrustful of sprays anywhere where surface contamination might cause problems with analogue circuits. Who knows what might be caught in any residue, or decide to use it as a food source.

IPA doesn't worry me.

For DeOxiting, I prefer a tiny drop of D100 on the end of a jeweller's screwdriver, carefully placed exactly where needed.

If necessary, I'd put such a drop in the right place, then add a drop of IPA to flush it inside a pot or whatever.

I share your dislike of just spraying contact cleaner about, especially on RF circuitry. I prefer to spray a little into the plastic lid of the can and then paint it on with a very soft bristle brush. Sometimes Lidl (a supermarket) do artistic events and they used to sell packs of 13 brushes for £1. They might be looked down on by the dedicated water colourist, but they are ideal for things like this. It can also be applied with a cotton bud, or cocktail stick or other suitable things.

IPA seems pretty benign, but the stuff to use for electronics is very pure and so leaves no residue. I recall it doesn't cost much more than lesser grades which contain water etc. You just have to look out for it. If you use it to any extent, it makes no sense to buy small bottles.

The point was to deliberately leave a silicone lubricant residue for the wipers and shaft. What do you think is in Fader Lube? There's a reason I warned to be careful of HV and Hi-Z areas of the circuitry.

"Sealed" pots are in general a dicksore, as you can't properly flush them out; the best you can hope for is that a trickle of solvent/lubricant gets to the wipers. I prefer to do that in one step and minimize the chance of cross-contamination and drying out the shaft; alcohol tends to take the grease from the shaft and carry it wherever it goes. The silicone spray seems to not do so nearly as much.

I suggest you try the food-grade silicone attack, maybe on something you don't think is mission-critical, like some old audio device. It does work for me, and it has brought back pots that were literally DOA.

mnem