Fluke 89 IV repair - help needed - Page 1
Forum section: electronics / repair

author: petermif
author_rank: Newbie
timestamp: January 19, 2020, 05:55:01 pm
content: Hi guys,My first postMy Fluke 89 had been in storage while I moved home and its batteries leaked out some electrolyte. When i opened it up the leakage seems limited to the battery compartment only so i thought i was lucky but once i cleaned it and put in new batteries it powers up ok by reads negative ohms!!Inside it looks new but I'm wondering about the yellow component with the slot in it (see picture) and also any ideas about fixing the negative ohms reading.Any help / advice is greatly appreciated.Thanks,Petermif

author: joeqsmith
author_rank: Super Contributor
timestamp: January 19, 2020, 06:27:09 pm
content: Slotted part is a spark gap, battery looking part is the super cap, other is a resistor.Is it a problem in all ranges? Do all of the other modes work, assuming you have a way to check them?

author: petermif
author_rank: Newbie
timestamp: January 19, 2020, 07:11:49 pm
content: Hi Joe,Thank for your reply. Yes the error is on all ranges of ohms but also on V and mV etc however i noticed that with the leads unplugged the meter reads OL on all ranges whereas with the leads connected and shorted i get a negative 30 ohms reading on all ranges but on the kohm range its -2.87k !! Also with the leads still shorted i get -2.7mVDC, -0.1344 VDC!!! Weird behaviour indeed!Is there a way to reset the meter or some other method to fix this?Thanks

author: andy3055
author_rank: Super Contributor
timestamp: January 19, 2020, 07:52:59 pm
content: You can download the service manual from below link and check the calibration procedure:https://elektrotanya.com/fluke_87-89_iv.pdf/download.html#dl

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 19, 2020, 08:43:28 pm
content: There isn't much point in going through any calibration before you're sure it has been cleaned of any electrolyte.Once correctly cleaned I doubt it will need calibrating at all.If it were mine I'd be making sure that the supercap is discharged or removed, remove shields, LCD, switches and wash the lot down.As an example the DMM in this galleryhttps://photos.app.goo.gl/uCUmZvgM6NLxzHAJ7was in quite the same case as yours, after several good toothbrush scrubbings in water, soap, vinegar, much rinsing, and a final scrub with WD40, this meter was back within tolerances.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 19, 2020, 09:01:12 pm
content: Quote from: shakalnokturn on January 19, 2020, 08:43:28 pmI agree. Don't touch any calibration.If there was battery leakage, clean the entire PCB first with IPA and gently scrub with a clean toothbrush.Let it dry thoroughly overnight or use a PC fan to blow on it.PS. There are many threads here on the forum where a simple IPA cleaning fixes negative ohms. There was either battery leakage or dirt/debris on the pcb. The dirt/debris may have entered when the user was changing the battery or fuse or the meter was just used in a dirty and dusty environment.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 19, 2020, 09:12:27 pm
content: Quote from: petermif on January 19, 2020, 05:55:01 pmTry eneloops instead of akaline next time if you forget to take out the batteries before long term storage.

author: z01z
author_rank: Regular Contributor
timestamp: January 21, 2020, 06:48:35 am
content: Quote from: shakalnokturn on January 19, 2020, 08:43:28 pmYou mean the PCB? I'm not sure that's a good idea.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 21, 2020, 08:17:57 am
content: Quote from: z01z on January 21, 2020, 06:48:35 amYes the PCB. I wasn't convinced it was a good idea either before trying, after repeated cleaning with the usual methods I still had the mV range above zero. The WD40 got that sorted.What harm are you expecting it could cause?