Gang Switch Maintenance - Page 1
Forum section: electronics / repair

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 10, 2016, 10:02:17 pm
content: I have one of these gang switch (or what is it called?) in a bench multimeter. I have found that the current ranges are not working because one of the contacts is not working.There is one pin going to the input of the measurement, and one each to the front and rear terminals. Not matter which position the switch is in (front or rear) neither one ifconnected.In the attached photo it is the last three pins on the bottom left. The second to last pin (B) is supposed to be connected to either the last pin (C), or the third to last pin (A) to choosefront or rear inputs. However, neither is contacting.What is the recommended first try cleaner maintenance? Should I go with contact cleaner like DP contact cleaner (cleaner degreaser). Or should I go with something like CRC 2-26?I know the CRC 2-26 does a great job of lubricating switches and pots, but it is conductive, and I wonder is its residue might impact this 6.5 digit meter negatively by causingsome leakage. For most switches I usually use the contact cleaner followed by a little CRC. But this being such a sensitive instrument I am having second thoughts.I could also just jump the pins to use the front inputs and call it a day, since I am not likely to measure current on the rear inputs.Thoughts?Thanks in advance.

author: Vgkid
author_rank: Super Contributor
timestamp: March 10, 2016, 10:26:44 pm
content: If cleaning doesn't work, just buy a new one. In older gear, they tend to go outright bad.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 10, 2016, 10:55:41 pm
content: Quote from: Vgkid on March 10, 2016, 10:26:44 pmAny idea how to find this particular one? I don't see a part number on it.

author: VK5RC
author_rank: Unknown
timestamp: March 10, 2016, 11:17:56 pm
content: Is that an HP 34401, if it is there are quite a few posts regarding the failure of the front to rear switch, how to pull apart, lots of little bits of different size, but it does appear to be repairable ( with effort) I think dr frank had some good tips.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 10, 2016, 11:39:59 pm
content: It's a Keithley 2100.(Cue the haters...)Actually, I gotta say I rather like this meter. The only real drawback with current firmware is that the settings are stored on power cycling. Honestly, not a big deal, though.This was an eBay score. So who knows its pedigree. It has (or had until I opened it) a current cal.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 11, 2016, 12:01:19 am
content: So what would you use to clean it?After cycling it a bunch of times I finally got it to work most of the time on the front inputs, which may be just fine. But I'd like to clean it, or see if I could get it to function as intended.

author: lowimpedance
author_rank: Super Contributor
timestamp: March 11, 2016, 12:43:55 am
content: The construction looks like it would be impossible to pull apart for a thourough cleaning, how ever there appears to be a small opening at the rear right near the contacts in question. And as you have managed to get some sort of function by cycling it I would try a little contact cleaner to start with through the small openeing the do some more cycling and see if it gets better !.I suspect though its not going to be a permanent fix, and as bodgy as it is jumpering may be needed sometime down the track if a new part cannot be sourced.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 11, 2016, 01:37:46 am
content: I ended up going the contact cleaner route, without the CRC 2-26. I just use AeroMagnolia's DP Contact Cleaner, which is an aviation product that leaves no residue, and is safe for plastic, etc.It worked!Of course we shall see how long it lasts, but I don't use that switch very often anyway.If it does end up continuing to fail then I will likely just jumper it in the Front position, and disconnect the rear current terminal wire (to prevent the front and rear from being shorted together).This little issue saved me $100 off the cost of this meter. The seller offered to take it back, or to try to fix it on their end, or to take some money off. I ended up getting it for almost $100 less than my Fluke 87V. Not bad for a 6.5 digit bench meter with 2 wire and 4 wire measurements, and a USB interface!The 2100 may not be a high end Keithley (it is a rebrand), but for the price (list around $800, I got it for well under half that) it is actually a really nice meter.Sure, people who use the multi-thousand dollar Keithleys on a daily basis will complain, but it is not designed to replace those units. That's like a Mercedes S-Class owner complaining about a C-Class. Or a (yuck) BMW 7-series driver complaining about a 3-series.Some of the front panel UI is a little screwey (overly complex), but nothing difficult to get used to. The majority of functions people would use are easily accessible, typically with one or two presses. It is easy to setup for remote control via USB either with the software from Keithley-- KI-Tool, which is pretty bare bones, or via python scripting. Most meters have some quirks. Hell, I watch EVERYBODY try to measure AC current on the Fluke 87V when they really want to measure DC current. (It defaults to AC current until you press the yellow button for reasons known only to John Fluke.)

author: Vgkid
author_rank: Super Contributor
timestamp: March 11, 2016, 05:31:55 am
content: Good job. A good cleaning fixed a power switch on one of my pieces. For that piece of gear, i would still replace it due to age(34y).

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 11, 2016, 07:05:52 am
content: Yeah, on the old stuff it is better to replace them *IF* you can find the part! Always a challenge.I am not sure how old this guy is, but the meter is relatively modern. I would guess 5 years or so. Pretty stoked to get a pretty nice meter (< $1kUSD) for so little cash.I gotta admit I am glad the current ranges failed initially, as I got $100 refund to open up a meter I wanted to open anyway, do about five or ten minutes of PCB trace following and continuity checking, and spray some contact cleaner in there. Not bad for twenty minutes of work of something that I enjoy. This is a hobby for me. So all this is learning and fun.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 11, 2016, 07:06:57 am
content: Should I bother putting some CRC 2-26 in there? Or do you you folks agree with my initial instinct that this might be more trouble than benefit?

author: lowimpedance
author_rank: Super Contributor
timestamp: March 13, 2016, 12:00:48 pm
content: Quote from: FlyingHacker on March 11, 2016, 07:06:57 amNO CRC, if it plays up again give it another squirt of contact cleaner and leave it at that.Good to see your happy with it.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 13, 2016, 05:07:10 pm
content: Lowimpedance, thanks for the reply. I went ahead and put it back together without the CRC.I find CRC helps contacts, but since it does conduct, and I think it might build up in that type of switch and cause problems.