Author Topic: Fluke 187 Component Identification & Repair  (Read 1753 times)

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Offline Dav2481

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Fluke 187 Component Identification & Repair
« on: April 01, 2019, 11:04:30 pm »
Hi All,

I've been fault-finding my Fluke 187 that I bought, history unknown.

I believe I have narrowed down the fault to a shorted resistor, but there are no markings or indicators as to what it could be. I'm currently going through service manuals for similar Fluke models to find out what the component may be, and thought I'd post this as well.

If you're curious, the multimeter displays erratic readings on all settings, e.g. 1 Volt AC with the leads connected or disconnected, and the resistance settings shows overload.

I've attached 2 photos of the board and the suspect part.

Thanks for your help!
 

Offline retiredcaps

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Re: Fluke 187 Component Identification & Repair
« Reply #1 on: April 01, 2019, 11:10:20 pm »
Resistors fail open.

The component in your picture is likely an inductor.  It should read very low ohms.

SMD resistors on the pcb usually have a marking on top of them. Like 103 resistor next to the inductor.
 
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Offline retiredcaps

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Re: Fluke 187 Component Identification & Repair
« Reply #2 on: April 01, 2019, 11:13:09 pm »
Answer all the questions completely.

1. Put meter in DCV.  With no probes, what does the lcd show?
2. Put meter in DCV.  With probes shorted, what does the lcd show?
3. Put meter in DCV.  Measure a 1.5AA cell, what does the lcd show?
4. Put meter in ohms.  With no probes, what does the lcd show?
5. Put meter in ohms.  With probes shorted, what does the lcd show?
6. Put meter in ohms.  Measure a 1k ohm resistor, what does the lcd show?
 

Offline Dav2481

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Re: Fluke 187 Component Identification & Repair
« Reply #3 on: April 02, 2019, 04:36:29 am »
Sorry about that, I must have missed missed it.

1. 0V. Jumps between 0.0004 to -0.0002 quickly. Seems like normal behaviour.
2. Same result as No. 1, but jumps around slower.
3. 0V. With nearly no jumping around.
4. OL (Overload).
5. OL (Overload).
6. OL (Overload)

 

Offline wictor

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Re: Fluke 187 Component Identification & Repair
« Reply #4 on: April 02, 2019, 04:52:05 am »
The big white input resistor above selection knob is probably open. Measure resistance between pins.

Input pin is nearest to those big green resistors. Resistance between first and second pin should be about 10 Mohm and others I don't remember. Check also that there are resistance between resistor input and positive input socket.
« Last Edit: April 02, 2019, 04:58:06 am by wictor »
 

Offline retiredcaps

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Re: Fluke 187 Component Identification & Repair
« Reply #5 on: April 02, 2019, 05:12:08 am »
Your input protection components could be bad.  All readings can be done "in circuit".

1. Yellow is the fusible resistor. It should measure around 1k ohm.

2. Red is the PTC.  It should measure around 1.1k ohm.

3. In blue are the MOVs. All 3 should read open circuit in resistance mode.

Report all measurements.
 

Offline shakalnokturn

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Re: Fluke 187 Component Identification & Repair
« Reply #6 on: April 02, 2019, 07:18:48 am »
Maybe cleaning function selector tracks and checking spring contacts are all there and in good condition could help too.
That looks a little dirty on your meter.
As for the state of the input section of your fluke you can actually get a quick idea on that just using another DMM and measuring the across the Fluke's socket.
 

Offline mzacharias

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Re: Fluke 187 Component Identification & Repair
« Reply #7 on: April 02, 2019, 12:44:15 pm »
Have you checked to see if the input jack assembly is bad? Common problem on these. Just plug the test leads into the 187, and measure the input resistance with another meter. Should be around 11 MegOhm.

The Fluke part number is 89-4-8002

I got mine from Newark. eBay sellers mark them up ridiculously.
 

Offline Dav2481

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Re: Fluke 187 Component Identification & Repair
« Reply #8 on: April 03, 2019, 09:38:20 am »
The big white input resistor above selection knob is probably open. Measure resistance between pins.

Input pin is nearest to those big green resistors. Resistance between first and second pin should be about 10 Mohm and others I don't remember. Check also that there are resistance between resistor input and positive input socket.

There is 3.5Ω between the input terminal and the resistor, and there is 10 MΩ between the input pin and common.

Every pin on the large, thin rectangular package seems to have a resistance. The smaller component labelled 10nk1000 (A capacitor?) appears to be open circuit when I check it for resistance and capacitance.



1. Yellow is the fusible resistor. It should measure around 1k ohm.

2. Red is the PTC.  It should measure around 1.1k ohm.

3. In blue are the MOVs. All 3 should read open circuit in resistance mode.

Report all measurements.

1. 0.954KΩ
2. 1.216kΩ
3. Red component: 101.4K
    Blue Component closest to red component: Open Circuit
    Blue Component closest to DF06S: 13.15MΩ

Might have a problem here.

Maybe cleaning function selector tracks and checking spring contacts are all there and in good condition could help too.
That looks a little dirty on your meter.
As for the state of the input section of your fluke you can actually get a quick idea on that just using another DMM and measuring the across the Fluke's socket.

Spring contacts look to in good condition, I gave the function selector tracks a clean and there was no difference. I think the problem lies in the input protection.
The socket seems to measure Ok, assuming 10MΩ is normal.

Have you checked to see if the input jack assembly is bad? Common problem on these. Just plug the test leads into the 187, and measure the input resistance with another meter. Should be around 11 MegOhm.

I measured 10MΩ, everything seems to be in order solder joint wise too.


Thanks for the help everyone! I didn't expect all the replies, it's been great.
 

Offline retiredcaps

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Re: Fluke 187 Component Identification & Repair
« Reply #9 on: April 03, 2019, 05:32:44 pm »
3. Red component: 101.4K
    Blue Component closest to red component: Open Circuit
    Blue Component closest to DF06S: 13.15MΩ

Desolder all 3 above and retest your meter.  There might be something more wrong, but let's remove the obviously bad components first.
« Last Edit: April 03, 2019, 05:34:39 pm by retiredcaps »
 

Offline retiredcaps

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Offline ModemHead

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Re: Fluke 187 Component Identification & Repair
« Reply #11 on: April 04, 2019, 01:17:10 am »
1. 0V. Jumps between 0.0004 to -0.0002 quickly. Seems like normal behaviour.
2. Same result as No. 1, but jumps around slower.
3. 0V. With nearly no jumping around.
4. OL (Overload).
5. OL (Overload).
6. OL (Overload)

These results point heavily toward something being OPEN in the front end.  The jack assembly problem that mzacharias mentioned is very common and definitely might cause this.  This is what it looks like:



It cannot be easily seen without removing the jack assembly, so do some continuity checks, press on the jacks, or whatever you can think of to verity that this is or isn't the problem.

The MOV measurements are also problematic, so definitely take them out and retest them as suggested.
 

Offline floobydust

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Re: Fluke 187 Component Identification & Repair
« Reply #12 on: April 04, 2019, 02:25:27 am »
There could be an open circuit on the input COM side.
Input COM goes through the chip ferrite bead and then a long skinny inner-layer trace running up to the DMM IC.

The ferrite bead is the one OP thought was shorted (by the bridge rectifier), but this is reading correctly as 40mohm. They crack in Fluke DMM's and go open if a meter gets dropped hard. Pressing test probes on a cracked ferrite bead can make it temporarily read OK, so instead use nearby pads/traces to check its continuity.

OP can also check continuity from input COM jack to the ferrite bead and nearby big via, and then at the other end of the long trace run to the DMM A/D IC Fluke 669918 AGND, possibly through a part then to pin 22. Pin 21, 23 are guards, like pin 25, 27.

more pics at: https://www.eevblog.com/forum/testgear/fluke-187/
« Last Edit: April 04, 2019, 02:32:44 am by floobydust »
 

Offline retiredcaps

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Re: Fluke 187 Component Identification & Repair
« Reply #13 on: April 04, 2019, 02:54:26 am »
The ferrite bead is the one OP thought was shorted (by the bridge rectifier), but this is reading correctly as 40mohm. They crack in Fluke DMM's and go open if a meter gets dropped hard. Pressing test probes on a cracked ferrite bead can make it temporarily read OK, so instead use nearby pads/traces to check its continuity.
Yeah, in some Fluke 170 series, we have had a number of reported bad beads due to soldering and such.

Example.

https://www.eevblog.com/forum/repair/fluke-179-76688/
 

Offline Dav2481

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Re: Fluke 187 Component Identification & Repair
« Reply #14 on: April 13, 2019, 02:22:03 am »
Hi All,

Sorry for the long delay in posting, life led me away from the bench.

I finally found some time to take a closer look at the input terminals, and found both of the legs connecting V+ and Common were disintegrated!

I'll order a new input terminal from eBay soon. I tested the multimeter against my Fluke 117 on DC and AC voltage, and they agree perfectly.

I was looking into cleaning the case of the meter, and I found ModemHead's guide, thank you very much!

I managed to dig up some service history on the meter, it came out of the ADF (Hence the ADF branding on the LCD, not sure if I had a photo of that), and it was decommissioned in April of 2017 from the HMAS Warramunga due to intermittent +v terminal connection. Pity the ADF doesn't repair them... My gain, right?  ;D
 

Offline ModemHead

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Re: Fluke 187 Component Identification & Repair
« Reply #15 on: April 13, 2019, 12:58:36 pm »
Excellent. Glad you got it sorted.  :-+

I was looking into cleaning the case of the meter, and I found ModemHead's guide, thank you very much!
Be sure to browse the comments on that article for more info and ideas.
 

Offline mzacharias

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Re: Fluke 187 Component Identification & Repair
« Reply #16 on: April 13, 2019, 01:16:04 pm »
Not sure what country you are in but you are likely to save about $25.00 US buying from Newark, Element 14, even with higher freight costs.

The Fluke part number is 89-4-8002
 


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