Fluke 187 "seeks" in high Ohms ranges

[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]

Doesn't it require an external high-voltage unit in this mode?

I can't imagine that it does.

Google "fluke 187 service manual"

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:

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)!

And:

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!

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).

[BeBuLamar]

Which part did you soak? I would like to do that with my 189. It's not too bad and can measure resistance in several megohms without problem but without touching the probe it indicates 200 Mega Ohms.

[mwb1100]

Which part did you soak?

The whole PCB. 

I removed the LCD first - I was scared that I'd snap one or more of the clips holding the LCD to the PCB, but thankfully that didn't happen.  Then I placed the PCB in the smallest plastic tub I could find that would hold it, and poured enough 99% IPA to cover the board. If I remember right, the IPA went about halfway up the input jacks.  I should have thought to take photos.

And a reminder of my mistake: take the fuses out to save yourself $10-15 or so replacing ones that get filled with IPA.

Then I left it for 24 hours.  I'd occasionally rock the tub to "swish" the IPA around, but I doubt that did anything.  After 24 hours, I took the PCB out , sat it down next to a small fan blowing on it for a day, flipping the PCB over occasionally.  I think it was less than 24 hours drying before I got impatient and reassembled and tested it.

I'm still surprised it worked.  There was absolutely no visible change that I noticed (other than the fuses, which went from white to a dingy light brown color from IPA seeping in).

[BeBuLamar]

Thank you! Thanks for confrming that you removed the LCD because i think the alcohol may hurt the LCD. Now I need to find the 99% Isopropryl Alcohol. I only have the 91% which has 9% water which we want to get rid off.
I have a good number of Fluke 287, 289, 87V but my favorite is the 189 and I can't send it to Fluke for repair Fluke doesn't repair such an old model any more (even though it's supposed to have the lifetime warranty).

[bdunham7]

Now I need to find the 99% Isopropryl Alcohol.

https://www.amazon.com/Amazon-Brand-Isopropyl-Antiseptic-Technical/dp/B07NFSFBXQ

$28 for a 12-pack. 

[BeBuLamar]

As I said my 189 wasn't as bad as mwb1100's 187 but when the 2 probes don't touch the resistance reading shows about 200 mega ohms. I soaked it in the 99% IPA for 24 hours then dry it off for a few hours. Put it back together and now it shows OL quickly when 2 probes don't touch. Great tips.

[mwb1100]

I’m still stunned at how effective that suggestion was.