Fluke 187 reads 2 ohms high

[Robomeds]

I thought I would turn to the forum with another DMM question.  I have a Fluke 187 that I thought was working perfectly in all ranges.  Today I noticed when I shorted the leads it was reading something like 2.3 ohms.  That seemed high so I tried with a jumper wire.  The reading was consistent.  Using that same wire in several of my other meters got resistance readings in the expected 0.05-0.3 ohm range.  Thus I feel confident that the resistance should be under 1 ohm.  I didn't get a chance to check to see if this offset exists at higher resistance ranges (say a 10k resistor reading 10.02 kohm) or it it's a true 2 ohm offset.  The voltage reading is spot on with several other meters.  The mA and uA current readings look good.  I connected the 187 in series with a few other meters and in all configurations I tried I got a consistent current reading.  The only reading I've seen that seemed off was the temp reading being 1* F higher than my other meters.  However, that is well within spec.  The 2 ohms vs an expected 0.1-3 ohms clearly is out.  Any suggestions?  The interior of the meter looks clean but it is possible a safety component is upsetting the readings. 
Thoughs?
Thanks

[retiredcaps]

The 2 ohms vs an expected 0.1-3 ohms clearly is out.  Any suggestions?

I agree that 2 ohms is not normal.

I would start with a basic cleaning as per modemhead's Fluke 189 blog

http://mrmodemhead.com/blog/gallery/fluke-189-clean-up/

especially at the input jacks with the q-tip dipped in IPA and the paper towel/straw dipped in IPA.

[Huluvu]

sounds like the Volt Input Jacks have some problems (e.g. cold solder joints)
I would check this first 

Good luck for successfully Repairing this great Meter 

[retiredcaps]

The interior of the meter looks clean but it is possible a safety component is upsetting the readings. 

You can always check the PTC.  It should around 1.1k ohms.

[Groucho2005]

Just checked my 13 year old 187 - When shorting the terminals it reads 0.04 Ohm.

[Robomeds]

Thanks all. I only noticed this late last night.  Today if I get a chance I will run a few checks.
First, I'll check the input impedance in DC mode.  Next, I will check to make sure the 2.x ohm offset is just 2.x ohms rather than say 20 counts.  I'll check by first by putting the meter in a higher range (1k vs 100ohm etc) then try measuring some 1% resistors I have with several meters.  I'm thinking this will help decide if we are dealing with a true 2.x ohm series resistance or a damaged safety component that is causing some parasitic error.  I will check the PTCs as well as look back at an older thread where Retiredcaps helped me fix my Fluke 87V (bad PTCs).  I don't remember the symptoms but I do recall that PTCs are a common thing to check.  I will also check the solder joins and clean the jacks. 

Thanks for the input all.

[DmitryL]

I thought I would turn to the forum with another DMM question.  I have a Fluke 187 that I thought was working perfectly in all ranges.  Today I noticed when I shorted the leads it was reading something like 2.3 ohms.  That seemed high so I tried with a jumper wire.  The reading was consistent.  Using that same wire in several of my other meters got resistance readings in the expected 0.05-0.3 ohm range.  Thus I feel confident that the resistance should be under 1 ohm.  I didn't get a chance to check to see if this offset exists at higher resistance ranges (say a 10k resistor reading 10.02 kohm) or it it's a true 2 ohm offset.  The voltage reading is spot on with several other meters.  The mA and uA current readings look good.  I connected the 187 in series with a few other meters and in all configurations I tried I got a consistent current reading.  The only reading I've seen that seemed off was the temp reading being 1* F higher than my other meters.  However, that is well within spec.  The 2 ohms vs an expected 0.1-3 ohms clearly is out.  Any suggestions?  The interior of the meter looks clean but it is possible a safety component is upsetting the readings. 

I had similar problems with my Fluke87. Disassembling it and cleaning PCB in ultrasound bath with IPA fixed problem entirely.

[Robomeds]

Thanks, I might try that.  I have access to an US bath.

[retiredcaps]

Free_electron used an ultrasonic bath to fix a Fluke 189 with a leads problem.

https://www.eevblog.com/forum/repair/fluke-189-teardown-repair/

[Robomeds]

Well I don't think it's the sockets.  I tried the range changing experiment.  It started at ~2.2 ohms in the lowest range.  Changing to the 1kohm range resulted in a measurement of around -0.002 ohms.  That is a negative resistance value.  Even in the higher ranges the shorted leads had a small negative resistance.  I'm going to try to get some IPA and do the bath tomorrow.

[Robomeds]

Update:
I did the PCB wash in the ultrasonic bath using a water IPA mix that was about 25% alcohol.  After 15 min in the bath I rinsed with 70% IPA then used compressed air to dry the whole thing.  It worked and all my resistance readings look good!
Thanks for the suggestions and help!

[Lightages]

So.... What is the design fault that allows such high end meters to go off from non-obvious contamination? Perhaps the grease they use for the function selector switch is migrating across the board? Any ideas?

[Robomeds]

No idea.  The sockets were fairly clean and dirty sockets wouldn't explain the negative resistance readings I was seeing.  I recently opened the meter so I'm probably at fault (that would also explain why I didn't notice this when I first got the meter).  Either way, the board looked really clean to me but the bath did the trick. 

[retiredcaps]

I did the PCB wash in the ultrasonic bath using a water IPA mix that was about 25% alcohol.  After 15 min in the bath I rinsed with 70% IPA then used compressed air to dry the whole thing.  It worked and all my resistance readings look good!

If you still have this Fluke 177, maybe try the same procedure?

https://www.eevblog.com/forum/repair/multimeter-repair-time-again!-fluke-177-reads-8-ohms/

[Robomeds]

Funny, I was about to mention the 177 but decided not to.  Yes, I actually tried it as well.  No dice.

For the reference of others, the 177 reads something like -0.9 ohm when shorted (auto ranging) and in the DC mA range reads a -530 mA current and, I just checked, draws 40mA from it's battery when on.  The board looks good so I've been at a loss as to what is wrong.  Sadly, I think it might be a short of some sort between the layers of the board but that is just a wide guess.  I simply can't find any visible damage.
 

[Muttley Snickers]

So.... What is the design fault that allows such high end meters to go off from non-obvious contamination? Perhaps the grease they use for the function selector switch is migrating across the board? Any ideas?

Not really related but recently both my cordless phone and universal TV remote started to play up and were not responding to button presses on particular keys, ok they are probably worn out on the carbon contacts I thought and in the case of the phone this was true and documented elsewhere on the forum, but the TV remote when inspected was full of a sticky grease like substance and after a thorough clean with IPA it seemed to come good for a few days but later the problem started to return so this time I hit it with methylated spirits instead and it is still going strong to this day.

In both cases it appears that the silicone membranes are breaking down and leaving residue throughout the entire internals of both devices even in spots where the membrane is not even close such as around the LCD displays, I have found that IPA although a fantastic cleaner can leave it's own film and this can readily be seen if you happen to clean your spectacles with it whereas with methylated spirits it is not as evident but the drawback is that metho has a tendency to dry everything out and from my experience it can make a dry solder joint worse which is not a bad thing in some cases.

Recently the neighbour brought something home from the local recycle shop and they write the price on goods with a white permanent marker and he asked me how to remove it, initially I recommended IPA thinking that nothing beats it and we gave it a try but this had virtually no effect on the markings so I then said lets try metho and low and behold it took it straight off without any effort.

From what I have read of late it seems that the most difficult process is determining whether the problem exists with damaged or out of spec components on certain devices or simply externally introduced or internally generated contaminants and in some cases both as I have recently found out with the phone, TV remote and to a lesser extent a restoration of a Fluke 83.

Regards

Muttley

[retiredcaps]

Funny, I was about to mention the 177 but decided not to.  Yes, I actually tried it as well.  No dice.

Re-continued back in the 177 thread with more questions and troubleshooting.

https://www.eevblog.com/forum/repair/multimeter-repair-time-again!-fluke-177-reads-8-ohms/msg779313/#msg779313

[SeanB]

TV remotes the most common cause of that film is the use of furniture polish in a can near the remote, which then accumulates in the unit. Done quite a few with cleaning with methylated spirits, and in many cases that, along with resoldering the IR led, the capacitor ( or adding a small capacitor that will fit in the case, typically I use a salvaged 6V3 470uF capacitor from old computer motherboards, choosing those that have not bulged and which have low ESR under 1R) and the 455kHz resonator, glueing down if loose with a small drop of superglue, and finally resolder battery springs and clean them up.

New batteries if the old ones are close to expiry ( though some had Duracell batteries 10 years old in them, still doing fine so left them) and close up the unit again. Some needed the case welded together to hold the battery door in because of broken plastic, so changing batteries is a service operation now.