M3900 Multimeter Malfunction, can it be fixed? - diyAudio
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Old 16th June 2013, 02:45 PM   #1
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Unhappy M3900 Multimeter Malfunction, can it be fixed?

Hi all,
A digital multi-meter (model - M3900, made by Mastech, bought last year ) is behaving in a strange manner. The display is not instantaneous like my other cheap one. It's showing a slow and gradual display of the reading.

For example, suppose I am taking a measurement of 12V AC, it is showing like 8....9....10....11.....12
and when I remove the probes, its going down like 11,10,9....0
And it's taking a considerable amount of time unlike my other one.

Can it be fixed?

Any help will be really helpful!
Thanks in advance.
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Old 16th June 2013, 02:49 PM   #2
Mooly is offline Mooly  United Kingdom
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Probably not worth or possible to fix at component level. If you are 100% sure the meter has not suffered spillage or some other accidental amage then I would remove the batteries and place (press) tinfoil over the whole PCB to remove any residual charge that may be holding some logic in a confused state.

If thats not an immediate fix then repeat leaving the foil in place but also leave it in a hot place for 48 hours and retest.

Other than that its probably pancaked
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Old 16th June 2013, 02:53 PM   #3
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Thank you sir )
I will clean the PCB with thinner and then do as per your suggestion and of course report you back.
I guess time to gift myself a new meter.
Could you kindly recommend a model that can measure capacitance too or that can be suitable for me in my hobbyist's situation?
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Old 16th June 2013, 05:56 PM   #4
Mooly is offline Mooly  United Kingdom
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I wouldn't use any chemicals on it unless the PCB is contaminated.

Haven't bought a meter in years so wouldn't know off hand what to recommend. Always worth buying a good one though.
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Old 16th June 2013, 06:12 PM   #5
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Just finished cleaning and dried.
Then double checked the existing tinfoil.
Latency lowered now.
But still the problem is there.
So ...... time to go shopping.

Thank you so much Mooly for you always extending helping hand. ))
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Old 16th June 2013, 06:27 PM   #6
Mooly is offline Mooly  United Kingdom
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Your welcome. Good luck with the meter shopping
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Old 16th June 2013, 08:04 PM   #7
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by csom View Post
Hi all,
A digital multi-meter (model - M3900, made by Mastech, bought last year ) is behaving in a strange manner. The display is not instantaneous like my other cheap one. It's showing a slow and gradual display of the reading.

For example, suppose I am taking a measurement of 12V AC, it is showing like 8....9....10....11.....12
and when I remove the probes, its going down like 11,10,9....0
Probably a relatively minor (but difficult to locate) problem: bad contact, split PCB track, fractured PTH, etc.
Could also be a blown fuse: sometimes, they leave a slightly conductive metal spray.
Check the main function switch, input connectors, etc: anything mechanical
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Old 16th June 2013, 09:05 PM   #8
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Thank you so much Elvee.
I re-soldered what I could earlier. Inspected the PCB carefully.
I will do it again in the daylight and post my success or failure.
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