Fluke 179 'floating' resistance?? - Page 1
Forum section: electronics / testgear

author: hannobisschoff
author_rank: Contributor
timestamp: April 18, 2020, 02:39:40 pm
content: Hi everyone. My Fluke 179 recently started acting strange. On the ohms setting, showing a resistance of 1.8 MΩ even though the leads aredisconnected. Anyone else ever had something like this?cheers!Image:

author: retiredcaps
author_rank: Super Contributor
timestamp: April 18, 2020, 06:54:32 pm
content: There are several things that could be wrong with your meter.1) Your meter is very dirty on the outside. When changing the battery or fuses, debris/dirt could have gotten inside your meter causing the non 0L ohm reading with no probes. A clean toothbrush and IPA bath will clean the PCB.2) Your 9V battery could have leaked and some dried up electrolyte is causing the 1.8M reading.3) You had an "oops" moment and the input protection is damaged. Your input protection consists of MOVs, PTC, fusible resistor. The MOVs should read 0L resistance, PTC around 1.1k ohm and fusible resistor is 1k ohm.4) Post a clear focused picture of your PCB, both sides, and we can help with the above.

author: hannobisschoff
author_rank: Contributor
timestamp: April 19, 2020, 02:38:44 pm
content: Sitrep: I opend her up and she seemed clean. Battery compartment clean and no obvious faults on the PCB... until I saw the input varistors.wiggled one a bit to prove my suspicion and now it's 'stuck' at 1.5MΩ when leads are open.How does one go about fixin this? Should I order the components and get in there myself, or should I send it to Fluke (or a fluke service provider near me)I've never measured anything above 400V ac or 10A. I did however once pop the 10A fuse when I connected an alternator to my bicycle and realized too late that It easily generated 50A

author: hannobisschoff
author_rank: Contributor
timestamp: April 19, 2020, 02:42:32 pm
content: heres another angle on the varistors. Sorry it's so blurry but my phone's camera is quite shit.

author: Fungus
author_rank: Super Contributor
timestamp: April 19, 2020, 02:51:43 pm
content: The MOVs look very suspect.. Grab another meter and measure resistance across them. It should be very high.

author: Shock
author_rank: Super Contributor
timestamp: April 19, 2020, 03:55:26 pm
content: Fluke uses Harris V910LSX1399 or Epcos/TDK S05K575 movhttps://www.eevblog.com/forum/repair/fluke-179-need-help-identifying-part/Littlefuse V575LA10PPanasonic ERZV10D911These have been recommended before as replacements, they may be slightly larger so check dimensions. You can remove the damaged mov or movs and the problem should go away. But you will have no input protection until they are properly replaced. A good idea to replace them all and have a few spares handy.

author: hannobisschoff
author_rank: Contributor
timestamp: April 19, 2020, 04:09:50 pm
content: Thanks for the help guys. Jup the MOV's are gonners. two of them measured 0.83e6 ohms and the other (slightly less burnt one) measured 1.8M. Will check out those replacements once the stores (hopefully) open upAny suspicion as to why they might've failed, since I am dead certain that I've never measured anything above 420V dc-ish. I did however use it on some 5kW motors back in University for an IGBT PI controller project. Could the EMF spikes be the culprit?Anyway, thanks again !

author: hannobisschoff
author_rank: Contributor
timestamp: April 19, 2020, 04:30:16 pm
content: Cannot find the above-mentioned replacements in South Africa, but I could find this, given the MOV Voltage and clamping current. The Panasonic ones are 12.5 mm and have a capacitance of 120pF, whereas these ones are 13mm and have a capacitance of 160pF. rest of the ratings are the same. Should I risk it?https://za.rs-online.com/web/c/passive-components/variable-resistors/metal-oxide-varistors/?searchTerm=varistor&applied-dimensions=4294461927,4294352445

author: Shock
author_rank: Super Contributor
timestamp: April 19, 2020, 04:33:55 pm
content: It's possible they got cumulatively worse over time especially if you are the second owner or let someone else use the meter or left it unattended. I've not seen any evidence they fail due to age but once they are degraded it may accelerate their failure further. Check the PTC resistance as well for ~1.1K and that 1k resistor. If the meter functions normally with the movs removed no reason to suspect any other problem.

author: Fungus
author_rank: Super Contributor
timestamp: April 19, 2020, 04:40:02 pm
content: Quote from: hannobisschoff on April 19, 2020, 04:09:50 pmYou can snip one leg of each of them while you're waiting (ie. make them very high resistance again). See if the meter returns to normal.Quote from: hannobisschoff on April 19, 2020, 04:09:50 pmDefinitely possible.

author: Shock
author_rank: Super Contributor
timestamp: April 19, 2020, 04:42:30 pm
content: Quote from: hannobisschoff on April 19, 2020, 04:30:16 pmThe other replacements are not exact either they are just the closest fit with the best rating. I've had a look myself and without going up in size it's hard to get better spec, I checked TDK as well. As I mentioned just recently in another thread the PTCs and MOVs Fluke uses were likely a custom part.

author: retiredcaps
author_rank: Super Contributor
timestamp: April 19, 2020, 06:34:28 pm
content: Quote from: hannobisschoff on April 19, 2020, 04:09:50 pmReplace all the MOVs. They are cheap enough.As for sending it to Fluke for possible warranty, they will look at the discolored MOVs and charge you $$$ to replace the PCB or entire meter. They will say the meter doesn't qualify for warranty as it was "abused" via discolored MOVs. The terms and conditions are spelled out clearly on page 3 of your manual.AFAIK, Fluke doesn't do component level repair. They would likely just junk the meter and send a complete replacement possibly for liability reasons?

author: hannobisschoff
author_rank: Contributor
timestamp: April 19, 2020, 06:38:52 pm
content: Replace all the MOVs. They are cheap enough.As for sending it to Fluke for possible warranty, they will look at the discolored MOVs and charge you $$$ to replace the PCB or entire meter.Will doFor interest sake: Are the component suppliers from your part of the world still operating, since RS here in SA is completely closed

author: HKJ
author_rank: Super Contributor
timestamp: April 19, 2020, 06:39:11 pm
content: Quote from: hannobisschoff on April 19, 2020, 04:09:50 pmInductive kickback is one of the thing the MOV's is supposed to protect against, but it can also kill them.

author: rvalente
author_rank: Frequent Contributor
timestamp: April 21, 2020, 12:26:14 pm
content: Quote from: retiredcaps on April 18, 2020, 06:54:32 pmI can't explain how aggressive some industrial environments, mechanical shops or industrial maintenance, they can get really dirty pretty fast (even you clean them on daily bases, the dirty gets in the polymer and stains it). Flukes are know to be reliable in those environments even not being IP rated