Fixing DMMs - Page 1
Forum section: electronics / general

author: PStevenson
author_rank: Regular Contributor
timestamp: March 28, 2012, 01:19:46 pm
content: more specifically the zebra strips.I've noticed more and more recently that there are kits available to restore your multimeter displays when digit segments have become faded and so on. in fact everytime I've bought a secondhand fluke I usually look for those with faded segments because they are cheaper.and everytime all I've had to do to fix this problem is take it apart and clean the contacts and zebra strips - without fail I've always gotten it working correctly.my question is this, is there some reason why cleaning zebra strips/PCB contacts isn't a reliable method of fixing this issue or are these LCD fixing kits available purely because people don't know that it's pretty easy to just fix the issue with a Q-Tip?my personal experience is 100% success and with the Flukes I've got, since I fixed the issue have never failed since however just because I've had success it doesn't mean it's fool proof - so is there any actual reason to go for a kit to fix the issue or not ?sorry if my writing is abit weird today, I'm not that well so everything is abit blurry

author: robrenz
author_rank: Super Contributor
timestamp: March 28, 2012, 01:24:58 pm
content: I have had the same success with just cleaning with IPA

author: FreeThinker
author_rank: Frequent Contributor
timestamp: March 28, 2012, 01:38:33 pm
content: I bought 5 DMM's off ebay as faulty (Maplin returns is my guess). Every one had the same fault, the plastic housing over the lcd wasn't clipped on correctly. One screw out of the back, a quick press on the housing and 5 good as new dmm's. Not bad for £7.60 +p&p.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: March 28, 2012, 01:44:01 pm
content: Quote from: PStevenson on March 28, 2012, 01:19:46 pmI think I read somewhere that Fluke found an issue with the rubber on the original zebra strips an respecified them. This is what the retro kits use (allegedly). But IMHO cleaning should be as good a fix as you need even if you have to do it on a regular basis (like every ten years or so)

author: entereev
author_rank: Contributor
timestamp: March 28, 2012, 01:47:02 pm
content: Well you answered the question yourself. Q-tip+IPA solution ain't the most reliable solution for long term, because it will happen again. It's a matter of when, not if.I assume the new elastomer strips are better, but only time will tell. Anyone here who bought those LCD fix kits?

author: robrenz
author_rank: Super Contributor
timestamp: March 28, 2012, 01:55:00 pm
content: I did my very old 87 about 5 years ago with IPA and it still looks like new. does it really matter if I have to open it up again in a couple of years?

author: Excavatoree
author_rank: Frequent Contributor
timestamp: March 28, 2012, 01:56:55 pm
content: I've never bought the kit (an e-bay seller sells one) because buying the strips directly from Fluke is so much cheaper. When I was more ignorant, I changed some strips, then quickly learned that cleaning the contacts and strips was usually all that was necessary.I've only seen one case where the strips were so worn that I had to replace them.The only other case is when one doesn't keep the strips in the same location and orientation - getting them mixed up sometimes causes the indentations made in the stip to not line up with the PCB contact pads.I try to not break the "glass to strip" seal, I've found if the strips stay stuck to the LCD, that contact is good. I clean the PCB side of ths strips and the PCB contacts and its' good.I always figure I can clean the existing strips and contacts first, as it doesn't cost me anything to try. Worst case, I'll have to use new ones.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: March 28, 2012, 02:11:54 pm
content: One more item:I've heard from a meter repair that one should not use isopropyl alcohol to clean PC contacts or zebra strips. He claims that it will "attact water" and will cause the repair to fail.I freely and readily admit that this sounds like BS (or other expression for "hogwash") but I have to admit that when I used non alcohol based contact cleaners, the repairs last longer. The first few meters I repaired all re-developed the problem, but I haven't had a relapse in any of the meters I've not used alcohol with. Anecdotal at best, non scientific, and possibly coincidental, but I thought I'd mention it.I'll also add that the 27/25 is my favorite system - six screws hold the PC board to the front case, sandwiching the LCD in between. Second best is the old 70 series, with four screws holding the PCB to the LCD bracket. I don't like the 87 "snap together model" system. I've replaced a lot of the "shield" assys that have their tabs broken off. (another item to buy from Fluke directly and not the e-bay seller, who makes a handsome profit) One has to know the part number, however.

author: Unknown
author_rank: Unknown
timestamp: March 28, 2012, 02:14:55 pm
content: Cleaning works most times. I fixed a couple of ancient flukes with paper or thin cardboard spacers to increase the tension onto the contact rubber.

author: robrenz
author_rank: Super Contributor
timestamp: March 28, 2012, 02:21:26 pm
content: I wonder what Deoxit D100L would do on the zebra strips?

author: PStevenson
author_rank: Regular Contributor
timestamp: March 28, 2012, 02:37:14 pm
content: I'll be brutally honest here and I know I'll get shit for it but I don't even bother with cleaning solution, I just use an abrasive pad for the PCB contacts till they're shiny again and wet the Q-Tip in my mouth for the strip - being acidic it tends to do the job but it's pure laziness on my partI would never bother touching the side that's connected to the LCD because I have in the past and it was a ballache to get the dam thing back on - it's never that anyway

author: icon
author_rank: Regular Contributor
timestamp: March 28, 2012, 08:49:01 pm
content: QuoteA little learning truly is a dangerous thing. IPA is highly hygroscopic, but it's also highly volatile. Once it's gone, it's gone - it doesn't leave a ghostly memory of hygroscopic-ness lingering like a fog. That said, there are varying grades of IPA, from 'rubbing alcohol', which contains who-knows-what, to virtually pure IPA. I keep a stash of pure-ish IPA from a lithographic supplies place, which is really handy for removing the sticky residue from stickers, cleaning whiteboards, mojitos and absorbing water from small components with nooks and crannies. If I put a drop on a watch glass and let it evaporate, there's no visible residue.John

author: Excavatoree
author_rank: Frequent Contributor
timestamp: March 28, 2012, 09:16:00 pm
content: Quote from: icon on March 28, 2012, 08:49:01 pmI suspect that using non pure IPA explains my experience, and it may explain the "anti IPA" person's experiences as well.

author: siliconmix
author_rank: Frequent Contributor
timestamp: March 29, 2012, 07:02:25 pm
content: if there's room cram some silica in there