repairing 80's kethley gang switches - Page 1
Forum section: electronics / repair

author: cnt
author_rank: Contributor
timestamp: November 23, 2021, 04:52:55 am
content: I picked up a used kethley 197 for CHEAP and It seems to have a faulty ohms switch, but is otherwise good. One of the "closed" contacts reads highZ unless wiggled (ohms switch pins 11-12). It kind of looks like I have to de-solder the whole bank of switches if I want to replace them, which frankly isn't going to happen.Has anyone fixed these switches in the past? Any tips/tricks? I can think of half a dozen hacks to get this working by adding an extra switch to the posts, but I'd rather not do anything hack unless I have to.I've circled the offending switch in red.

author: ataradov
author_rank: Super Contributor
timestamp: November 23, 2021, 05:15:28 am
content: Start with deoxit or any other contact cleaner. Chances are that's all you need to do.

author: David Hess
author_rank: Super Contributor
timestamp: November 23, 2021, 05:39:50 am
content: I find that squirting contact cleaner in and operating the switch restores proper operation.The switches come part pretty easy without unsoldering but access needs to be gained.

author: ataradov
author_rank: Super Contributor
timestamp: November 23, 2021, 05:46:22 am
content: Those switches have a hole on the bottom, perfect for contact cleaner spray. And metal frame has corresponding hole, so no disassembly is needed.

author: cnt
author_rank: Contributor
timestamp: November 23, 2021, 06:52:10 am
content: Awesome thanks for the tips! If things go sideways and I do need to disassemble is there documentation or a write up on how to disassemble those switches?Also I have some "QD Electronic Cleaner" that I use in automotive applications. I've not used it on anything sensitive before. Since this has a Gohm input impedance I'm kind of paranoid about leaving residue on the PCB.

author: ataradov
author_rank: Super Contributor
timestamp: November 23, 2021, 07:02:48 am
content: The switch body itself can't be disassembled, but you can find replacements.Don't use that stuff. Look specifically for "contact cleaner". I guess it is typically a contact cleaner too, but its applications make me think twice. I would at least compare the ingredients with deoxit.

author: cnt
author_rank: Contributor
timestamp: November 23, 2021, 09:00:31 pm
content: I emailed CRC's "technical service" email asking about their "electronics cleaner" vs their "contact cleaner". It sounds like either is okay and neither leaves any residue. Their MSDS seem to both indicate they're just solvents and propellants in the can too.I did order the deoxit though since it sounds like deoxit has lubricants in it that are helpful for switches long term. I'm just going to be careful how I apply it to get it only into the switches.For posterity sake and in case it helps anyone else here's what CRC said:QuoteI then asked if I should go out and buy the "contact cleaner" if I already had the "electronics cleaner" for cleaning switches in test equipment and this is what they said.Quote

author: David Hess
author_rank: Super Contributor
timestamp: November 24, 2021, 10:03:11 pm
content: Quote from: cnt on November 23, 2021, 09:00:31 pmThat is exactly the wrong type of switch cleaner to use. By itself, it will destroy the switches.These switches use a wiping action so they must be lubricated after cleaning to prevent the contact surfaces from being destroyed. A combination contact cleaner and lubricant is called for.