[volt-nuts] OCD About My HP419A Attenuator Switch Gold Plated Contacts

ed breya eb at telight.com
Wed Mar 11 04:43:25 EDT 2015

Yes, you are being a little too OCD about this. Instrument washing 
issues come up often, and there are plenty of opinions available - 
here are some of mine:

In the 419s that I have, the battery leakage crud has not gone beyond 
the circuit boards or maybe the edge connectors. Cleaning the boards 
should take care of it, and it's not that complicated. For stubborn 
alkaline deposits, a vinegar wash (if necessary) should neutralize 
and descale, followed by scrubbing with liquid dish detergent and a 
toothbrush, and then lots of rinsing with hot tap water and finally 
thorough drying - preferably with an oven, but air drying for a 
couple of days should suffice. Blasting with compressed air helps to 
get most of the water out.

Don't bother with pH indicators - I doubt they would show much unless 
there's so much crud that you can see it anyway. If KOH has gotten 
onto any critical circuits, it could cause symptoms such as excessive 
leakage currents, since it's hygroscopic and would tend to be ionized 
and conductive on the surfaces. If you are concerned about the 
switches, you can wash the whole thing with tap water and liquid 
detergent. First, remove or protect the meter movement and any 
batteries, and maybe the pilot light. As I recall, the rest is pretty 
much open so easy to flush out. There are different schools of 
thought about items such as power transformers and pots - you have to 
apply judgement on whether they will wash out and dry OK. If in 
doubt, protect them from the washing process.

When washing electronics, always finish with an alkaline (like liquid 
detergent) to neutral (water or alcohol) step before rinsing - you 
don't want any acidic residue left anywhere. Lots of rinsing and 
thorough drying is always good - several days of air drying for a 
whole instrument. You may have to relube some of the switches - I 
don't recall if they have grease on the contacts or mechanisms.


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