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| Fluke 187 "seeks" in high Ohms ranges |
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| mwb1100:
I have an old Fluke 187 that I got a long while ago off of eBay. It works well except that in the high Ohms range it seeks down toward the correct value (except when open circuit) for a long time. Like minutes. To be honest, I'm not sure if it ever reaches the correct value - I'm not patient enough to see. When it's reading ohms with an open circuit (no probes for example) in the 500M Ohm range (whether manually or by auto-range) it still seeks downward. Doesn't this in other ranges. A couple videos: - Fluke 187 seeking 440k ohm - Fluke 187 seeking resistance on open circuit I'm hoping the problem can be narrowed down to a simple replacement of an easy to get part. But I'm not nearly knowledgeable enough to know where to start looking except by asking here. When I look at the PCB there is no damage that's apparent to me, but maybe someone here can see something on the photos that I miss. If not, any suggestions about what I should test? |
| siealex:
Doesn't it require an external high-voltage unit in this mode? |
| Fungus:
Google "fluke 187 service manual" |
| mwb1100:
--- Quote from: siealex on August 20, 2023, 09:09:02 pm ---Doesn't it require an external high-voltage unit in this mode? --- End quote --- I can't imagine that it does. --- Quote from: Fungus on August 20, 2023, 09:39:04 pm ---Google "fluke 187 service manual" --- End quote --- Thanks. I found links to a non-Fluke document that was auto-translated from the Chinese original in this forum post: Re: Fluke 187/189 repair There seems to be a couple things that mention problems with the high Ohms range: --- Quote ---Once the motherboard gets wet, it will cause PCB Board leakage, there will be a lot Problems such as: resistance file open circuit is not displayed OL How many M The resistance of O, the DC voltage range does not return to zero has a great base, the current range is d Show OL Or give the alarm randomly, the measurement error is very large, if In the case of current leakage, the specific solution is: disassemble the entire motherboard Come out with 95% Pour the alcohol into the container, soak the motherboard completely Soak in alcohol container twenty four More than hours, then take it out to dry, Why do you want to soak the motherboard with alcohol instead of brushing it with a brush Motherboard because 187 The motherboard is 6 Floor PCB Board, once it gets damp, a lot of through holes will also cause leakage. If you use a brush to Middle layer PCB It can’t be brushed, but if you use a container to Soak completely, then the entire motherboard can be attached, so that Make PCB Where there is leakage in the via or middle layer line, pass The method of soaking alcohol can also be solved. (Pro test! The main board leakage failure caused by damp, soaking wine High precision maintenance success rate 95% the above)! --- End quote --- And: --- Quote ---3 : O block (electric barrier) normal display should be OL Readings, If two test leads are open, and the display 1M Reading above O Number, it means that the meter is faulty or the main board is Hole leakage! --- End quote --- I think these are both saying that the likely cause of not getting "0L" with an open circuit resistance reading is that the board might have some moisture damage ("hole leakage"?) and that soaking it for 24 hours in 95% IPA then letting it dry may drive the moisture out. That's certainly something I can try. I have a lot of 99% IPA from when I panic bought at the start of the pandemic in case we would need some homemade sanitation stuff. I'll give it a whirl. If it works, I'll be pleasantly surprised. Can't hurt, right? (someone please tell me if this could make things worse!) |
| mwb1100:
Unbelievable! IT WORKED! I soaked the 187's PCB in 99% IPA for 24 hours, let it dry off with a fan gently blowing on it for several hours. And now the Ohms function settles within a few seconds regardless of the range, and with no probes it stays at "0L" forever. One thing I should remind anyone who might try this: remember to remove the fuses. I didn't, and it's pretty evident that IPA made its way inside them. So out go those fuses and in go a couple replacements (at $8 a pop or so). |
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