Re: Stuck switches on 453


greenboxmaven
 

In addition to the volatiles evaporating, the grease or oil can oxidize into varnish. This is greatly enhanced by moisture. I have had great results for many years using synthetic engine oil such as Mobil 1 0W-15 and heat to liquify the varnish. Put a few drops of the oil on the shaft and bushing, them heat the shaft where it goes into the bushing with a soldering iron until the oil is sizzling, add more oil as needed to maintain the heat bridge to the shaft and bushing. Remove any plastic couplings, gears, or knobs that could be damaged by the heat before you start. Work the shaft back and forth carefully until it frees up, be patient, if you don't get results at first, be sure there is a drop of oil on the shaft where it enters the bushing and let it cool. It may require a few heating-cooling cycles with the oil applied before it frees up, once it does, flush the oil and crud out thoroughly and re-lubricate with the synthetic oil. Then, use a contact cleaner of your choice for the pot or switch contacts.

Bruce Gentry, KA2IVY

On 8/1/20 12:02 PM, Gary Robert Bosworth wrote:
So often, it is the grease that was used as a lubricant and the volatiles
evaporated leaving a dried up paste.

On Sat, Aug 1, 2020, 08:58 Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

David (and others):

Yes, my problem is the same as yours: The variable knobs on Ch. 1 and 2
Volts/Div are frozen, and are stuck in the uncalibrated mode. I???ve tried
various compounds...some for switches, some for pots, but no joy. Colorful
Anglo-Saxon expressions haven???t helped, either. Just NOT going to budge,
either one of them. Don???t know if it???s switches or pots that are binding.

But, since I mostly want this scope in Calibrated mode (and not
Uncalibrated, where it is locked-up now), I???m thinking I will just bypass
the switches and live with it. That???s what I???m thinking.

R



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