Products > Test Equipment

FLUKE 189 DC reading problem [with video]

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kamcm:
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!



CDaniel:
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 .

kamcm:

--- Quote from: CDaniel 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 .

--- End quote ---


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!
 

CDaniel:
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 .

kamcm:

--- Quote from: CDaniel on July 13, 2019, 04:09:47 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 .

--- End quote ---


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





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