Author Topic: FLUKE 189 DC reading problem [with video]  (Read 1220 times)

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Offline kamcm

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FLUKE 189 DC reading problem [with video]
« on: July 13, 2019, 12:14:35 pm »
When I use my Fluke 189 to measure 10.000V DC,
The measure reading is 8.888V  , I feel lucky with this number but I still want to fix it :-DD
Since it didn't happened all the time, It's really hard to find out the root cause.:-//





I checked all the input protection and it seems they are fine.
I have clean the gold plated trace under the rotary knob as well but the problem remain the same.


Actual input 5V
Reading 4.8V

Actual 10V
Reading  8.888

Actual 14V
Reading  13V

Actual 19V
Reading  18.010V

Actual 20V
Reading  19.038

Actual 21V
Reading  19.076


Actual 22V
Reading  20.643V


Actual 28V
Reading  26.6V



When I use the 189 to measure 20V, it will display 19.038V and
When I use the 189 to measure 21V, it will display 19.076V only

I wonder to know which component will likely cause this 0.04V different on the Fluke 189 meter in that specific voltage range?

Please advice,

Thanks!



« Last Edit: July 13, 2019, 12:20:17 pm by kamcm »
 
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Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #1 on: July 13, 2019, 01:54:41 pm »
When is starting OK you can use it normally if you leave it on ? Maybe  a input MOV is dammaged and start to conduct sometimes when voltage is applied .
 
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Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #2 on: July 13, 2019, 03:59:03 pm »
When is starting OK you can use it normally if you leave it on ? Maybe  a input MOV is dammaged and start to conduct sometimes when voltage is applied .


I decided to stress test my 189 with my megohmmeter to see if anything go wrongs with input resistance.

with 500V, having 10M input resistance, everything looks good.

But with 1000V...... it down to 8.38Mohm input resistance only. Somethings obvious not okay.  :palm:




I also tested my 179 and it remain 10M input resistance during 1000V stress test.



Which components is failed in my 189?? Is it the MOV or PTC ?
How can I found it out without de-solder those components?

Please advice,

Thanks!
 

Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #3 on: July 13, 2019, 04:09:47 pm »
The PTC is in series with the input ,  the MOVs are in parallel , so those could leak some current . I don't think you can be sure without desolder them  and see if it measures OK .
« Last Edit: July 13, 2019, 04:18:15 pm by CDaniel »
 
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Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #4 on: July 13, 2019, 04:29:57 pm »
The PTC is in series with the input ,  the MOVs are in parallel , so these could leak some current . I don't think you can be sure without desolder them  and see if it measures OK .


Thanks anyway.

I just watch this and I think it's more likely the MOV are failed.
https://www.youtube.com/watch?v=zUhnGp5vh60&feature=youtu.be&t=1300






Offline retiredcaps

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Re: FLUKE 189 DC reading problem [with video]
« Reply #5 on: July 13, 2019, 10:09:01 pm »
Which components is failed in my 189?? Is it the MOV or PTC ?
How can I found it out without de-solder those components?
Use your working Fluke 179 to measure the 189 PTC and MOV.  You can do this in circuit without desoldering them.

The PTC should be around 1k ohm.  The MOVs should all read 0L resistance.

If the MOVs are not 0L, you can desolder them, for test purposes, and retest the 189 to ensure it works properly.  The MOVs will then need to be replaced.
« Last Edit: July 13, 2019, 10:10:36 pm by retiredcaps »
 
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Offline Mr. Scram

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Re: FLUKE 189 DC reading problem [with video]
« Reply #6 on: July 13, 2019, 10:11:18 pm »
It seems to me that 1000V tests are a bit close to the rated maximum.
 

Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #7 on: July 14, 2019, 05:53:22 am »
In this case  the failure is not as straightforward for a simple resistance check in circuit ... if you read the first post sometimes behave normal . That's why the conclusive test would be to desolder the MOV and check it outside , or check the meter without the MOV if the readings are correct .
 

Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #8 on: July 14, 2019, 10:23:25 am »
I just de-solder all those MOV and check them one by one. 8)
I am not sure about the red one (6838)? What's it spec ? Is it also able to sustain more than 500V too?  :-//






Both blue MOV check with 500V they are good



The red MOV is fine when testing with 250V, it got OF.  But when I test it with 500V, the reading drop down to 0.408M.




Please advice,

Thanks!





« Last Edit: July 14, 2019, 11:51:23 am by kamcm »
 

Offline joeqsmith

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Re: FLUKE 189 DC reading problem [with video]
« Reply #9 on: July 14, 2019, 11:52:18 am »
Not sure why you would pull the MOVs but now that they are out, just repeat your low voltage test.   From your video, it appears to be a mechanical problem.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #10 on: July 14, 2019, 01:12:30 pm »
Not sure why you would pull the MOVs but now that they are out, just repeat your low voltage test.   From your video, it appears to be a mechanical problem.

You're right. Still getting the same problem with MOV removed.
Do you have any suggestions? which parts are likely having problems?

Thanks!

Offline joeqsmith

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Re: FLUKE 189 DC reading problem [with video]
« Reply #11 on: July 14, 2019, 03:54:26 pm »
From your video, doersn't it appear to be in the switch area to you?  I am not sure why you would think this is a component problem.  It could be a solder fracture but I wouldn't start reflowing everything like I see some idiots do. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #12 on: July 14, 2019, 04:40:52 pm »
From your video, doersn't it appear to be in the switch area to you?  I am not sure why you would think this is a component problem.  It could be a solder fracture but I wouldn't start reflowing everything like I see some idiots do.

It's because solder fracture will not lead to the input resistance drop down from 10M ohm to 8.38 M ohm (in #3).
It's more likely some components leaking current to the GND and causing this happened. That's why I decided to give it a try and de-solder the MOV.


Offline joeqsmith

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Re: FLUKE 189 DC reading problem [with video]
« Reply #13 on: July 14, 2019, 04:56:13 pm »
Your video shows it very intermittent.   This is not typical of a component failure.  Not sure why you would think that a fracture could not cause this symptom.  Looking at your video, it seems like the problem is in the switch area. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #14 on: July 14, 2019, 04:56:36 pm »
We don't know if the rest of functions work ok , just assuming from the initial post and video that the fault is only on Vdc .
Also , when is measuring OK what happens if you touch the switch , turn it just a little bit , apply pressure and so on ...  And I asked if you can use it normally when it is ok  , measuring different voltages for some time .
The big question is , you did something obvious wrong before the issue appeared ?
 

Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #15 on: July 14, 2019, 06:40:22 pm »
We don't know if the rest of functions work ok , just assuming from the initial post and video that the fault is only on Vdc .
Also , when is measuring OK what happens if you touch the switch , turn it just a little bit , apply pressure and so on ...  And I asked if you can use it normally when it is ok  , measuring different voltages for some time .
The big question is , you did something obvious wrong before the issue appeared ?

This problem happened on other functions as well.


In this video, you will see it jump to the correct value with a long time delay.

I think the Knob is not the root cause. I already try to apply extra pressure on the knob to test it.

The meter works perfectly before but suddenly this problem appeared.   |O


« Last Edit: July 14, 2019, 06:42:27 pm by kamcm »
 

Offline coromonadalix

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Re: FLUKE 189 DC reading problem [with video]
« Reply #16 on: July 14, 2019, 07:30:47 pm »
have you checked its super capacitor ?? if its rusted or has leaked ???
 

Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #17 on: July 15, 2019, 12:31:53 am »
have you checked its super capacitor ?? if its rusted or has leaked ???

It's rusted but I don't see a substantial leak.


Offline coromonadalix

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Re: FLUKE 189 DC reading problem [with video]
« Reply #18 on: July 15, 2019, 01:16:50 am »
I dont want to drag your post, but if you dont need time related logs   gently remove it to be sure,  when this puppy goes bad,  you may have excessive battery current draw or an leakage on the pcb,  removed mine on my 3 fluke 189 until i bought an substitute.

They are known to cause some problems  in the fluke 89IV - 189 and 287 or 289
 
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Online windsmurf

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Re: FLUKE 189 DC reading problem [with video]
« Reply #19 on: July 15, 2019, 01:37:57 am »
You might also try Mr.Modemhead's fix (full IPA cleaning of the board).
 

Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #20 on: July 15, 2019, 09:21:09 am »
I dont want to drag your post, but if you dont need time related logs   gently remove it to be sure,  when this puppy goes bad,  you may have excessive battery current draw or an leakage on the pcb,  removed mine on my 3 fluke 189 until i bought an substitute.

They are known to cause some problems  in the fluke 89IV - 189 and 287 or 289

I just de-solder the battery off the board and clean the spot under the battery.
But still having the same problem.  :-//

Offline coromonadalix

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Re: FLUKE 189 DC reading problem [with video]
« Reply #21 on: July 15, 2019, 10:43:53 am »
Has windsmurf wrote : do you have any contaminants on the board ??   Any solder residues ??   under the rotary knob functions, is there any grease / too much grease ?

Or Maybe your meter need some calibration ??



I have my oldest fluke 189 showing a strange behaviour only in ohms measurement under 10k ohms, the ohms ranges seems to works fine, but this one in a 27mhz rf section doesn't show the same values as my other 189 ??,  tested all ranges with references resistors, all is ok,  all input impedances are fine, but in my rf circuit i have a strange error ??  Maybe its the Fluke asic ic who as a problem ??

 

Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #22 on: July 15, 2019, 01:20:20 pm »
Should be tested on all functions , maybe if we know what is working right and what is not will figure out the cause .
 
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Offline kamcm

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Re: FLUKE 189 DC reading problem [with video]
« Reply #23 on: July 15, 2019, 02:51:48 pm »
Here is the test on every functions.  Any help would be really appreciated :)

=====================
AC

ACV
Actual 5V
Measure 4.72V

Actual 0.3V
Measure 0.0111V

AC HZ
Actual 50.00Hz
49.96HZ to 50.02 HZ, keep jumping

-------------------------------
AC mV

Actual 300mV
Measure 283.94mV

AC (mV) HZ
Actual 50.00Hz
49.96HZ to 50.02 HZ, keep jumping


======================

DC

Actual: 10V
Measure: 8.888V

===============
DC mV

Actual: 500mV
Measure: 470.72mV


=================
ohm

actual: 1ohm
measure: 0.06ohm

actual: 5ohm
measure: 0.19ohm


actual: 10ohm
measure: 0.38ohm

actual :20ohm
measure: 0.79ohm

actual: 50ohm
measure: 37.66 ohm

actual : 100ohm
measure: 88.93ohm

actual : 1k ohm
measure: 0.8893 kohm

actual: 5k ohm
measure: 4.6855 kohm


=================

mA

Actual : 20mA
Measure: 19.856mA

Actual: 10mA
Measure: 10.072mA

Actual: 5mA
Measure: 5.214mA

Actual: 4mA
Measure: 4.062mA

Actual 3mA
Measure: 2.763mA

Actual 2mA
Measure: 0.076mA

Actual 1mA
Measure: 0.038mA


===================

Actual : 100uA
Measure: 101.31uA

====================






Offline CDaniel

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Re: FLUKE 189 DC reading problem [with video]
« Reply #24 on: July 15, 2019, 08:16:44 pm »
So pretty much everything is bad and in the low side ... the schematic for this meters I don't think it's available but you should try to find and measure the precision voltage reference and power supplies for the analog part ,  before condemning the ASIC chip itself ...
The input protection can't explain the current measurement being off ...
« Last Edit: July 15, 2019, 08:28:35 pm by CDaniel »
 


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