Removing Carbon Tracks

[KA8WTK]

All,
  Just removed the band switch from the 812 rig I am restoring to find carbon tracks on the ceramic centers of the switch. This helps explain why it has acted so funky and blown so many fuses. The tracks are probably a result of the output coil arcing between the center link and the split tank a while back.
  Anyway.......What is the best way to remove the tracks from ceramic? Dishwasher? Scrubbing? Chemicals? All of the above? Scrap switch and look for another 4-gang 4-postion ceramic rotary switch (Mallory 164-C)?

Bill 

[WD8BIL]

There's only 2 things you can do Bill.

1) Machine or gently file the contaminated ceramic.
2) Throw it out and start over.

Simple washing or chemical treatment will not get the carbon outta the ceramic. Eventually it will arc again in the same place.

What kinda switch is it. I gots a boatload of ceramics that'll probably fit the bill. (no pun intended)

[KB2WIG]

                   "do all XYLs act a little strange "      As far as I can tell, yes they do.  Check out the archived posts r/e  marrage ; I don't have the time to look for them for you, the warden wants to go see the mom-in-law now....   klc

[KA8WTK]

Looks like this Bud.....

[WQ9E]

I have rescued one switch wafer by cleaning it in an ultrasonic cleaner.  I used a non-flammable parts washing liquid for the first pass and then rinsed and did a second cycle with some slightly diluted dish washer detergent.  I then rinsed it completely and let it bake in a toaster oven for a couple of hours.  This was a lot of trouble but it was an oddball switch wafer in a neat 40's era homebrew rig I picked up at a hamfest so I wanted to save it.

The ultrasonic cleaner was the cheap Harbor Freight unit and it is too small for big items but perfect for knobs and small electrical parts.  It is interesting to see foreign material burst forth in little clouds as the cleaner operates.  It was a fairly cheap experiment for $19.95 but I will probably buy a better unit (larger capacity and greater cleaning power) based upon finding even this inexpensive unit to be quite useful.  Some HF items are fine but almost everything is from China and like the vacuum tube factories their the quality control is questionable.  I also bought a pair of very long nosed needle nose pliers and they have been very useful; on the other hand the replacement 500 watt halogen light bulbs have an average life roughly akin to a snowball in Hades...

Rodger WQ9E

[W3SLK]

Windex works pretty good in those UT cleaners. That is what we use at work.

[WD8BIL]

OK Bill.... I'm sure I got a section or 2 in the junk box.

In high RF circuits you really don't wanna clean it and put it back in. Trust me... I know. It'll work in a pinch if ya baby it but ya won't be able to swing that monkey without it crappin' on ya again.

[KA8WTK]

Close inspection would tend to show both. Where some of the arcing occoured there does not seem to be a loss of metal. However, one spot in particular has some of the rivet that holds a wiper almost gone.

[W1RKW]

I've had carbon tracking develop on switches especially switches that carry substantial voltage that were sprayed with contact cleaner.  Overspray residue from the cleaner contributed to the carbon tracking.

[Mike/W8BAC]

On a parallel subject I did fix a bad switch arc problem in a Johnson KW match box. As some of you know the band switch has the stationary contacts mounted on hard asbestos tile like boards. A previous owner must have had some antenna problems or keyed into the tuner without an antenna. The Zorch looked imposable to fix.

I work near asbestos abatement people often and followed safe work practices. I disassembled the switch and scraped the hard asbestos board Well below the burns. Cleaning and inspecting the work as I went along. When I was absolutely convinced ALL remnants of the flash had been scraped clean I washed the boards with 99% alcohol, let dry and painted on Corona Dope from GC Electronics. No more problems! This won't work with a ceramic switch but it might help others with similar problems. A few other details are omitted here. If you want more info, just ask.

Mike

[WBear2GCR]

Ordinary carbon deposits on glazed ceramic usually come off with thinners or alkaline cleaners like "Mean Green" or spray type 'grill cleaners' or 'degreasers' - one or two up the scale from Fantastik or 409 - although try them first.

If the metal parts will stand it, and/or if it can be selectively applied, lye or oven cleaner will etch off both the carbon and any metalization... alternately an acid will proably do the same trick.

The problem comes in with how it will react with the silver plating and the other metals... so selective application may be required if the thing is truly arc'd into the ceramic and metalized as well.

It's easier on big heavy switches than little ones.

The little ones, once out of the rig, you can dissassemble the wafers and get at it that way...

Then once etched off and cleaned, if the glaze is gone, you may want to apply some insulating material, like a HV varnish (anti-corona dope) or even silicone rubber may suffice.

I've also mechanically abraded the etch track and had that work - depends a bit on the real depth of the track and the extent of the damage & conductivity...

Ymmv.

          _-_-bear

Oh in extreme cases, wax is a very good means of making a protectant to keep chemicals from acting on something... you might be able to dunk the switch in hot wax a few times, build up a protective layer, and then mechanically remove most of the wax from the "bad" area, clean the surface with a thinner that melts the wax, then do the heavy duty dunk routine... as a last resort for maximum attack.

[k7yoo]

Chemicals, scraping, etc are a waste of time. Scraping only drives the metallization deeper and makes the problem worse. I have saved and reused many ceramic components using my glass bead machine.
Remove the zorched contacts and hardware
BEAD blast (no sand please!) the carbon and metal residue off until the ceramic is clean and white. If you want to seal the ceramic (not absolutely necessary) use a HV conformal coating or corona dope.
reassemble with replacement hardware from a donor switch-attach using screws instead of rivets
I have fixed the following :
TL 922 bandswitch, BTI bandswitch, Johnson KW matchbox, Large B'cast ribbon inductors, etc., etc. I intentionally buy this junk knowing I can fix it
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