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UNI-T Digital Multimeter Faulty From Time Of Purchase

By Jestine Yong on January 28, 2022

I purchased this uni-t metre model: UT39A+ on January 2020 brand new from a local shop in the city. I did bought it because of its high capacitance mode(Mega/farad) compare to my other meters (suoer,dt9205a) brands that have limited measurement (200 microfarad).

So about a month after, I wanted to use the resistance mode,to my surprise the 400ohms, 4k, 40k mode were showing voltage range(faulty) but 400k, 4M, 200M are in good order.See picture below:

I guess this fault is from factory, so I wrote to the factory and one Mr Tony replied me, see it below:

Hello,

This unit is abnormal, but it can’t repair at your side. If this unit in the warranty year (from purchase date within one year), you can contact with local distributor (you buy from who) for the replacement.

Please let me know if you have any problems, thanks.

Have a nice day.

Tony

The local seller don’t take responsibility for such fault, so I was using only the capacitance mode when needed. July 2021, I decided to do something about it, so I opened its back case and tested all testable components on it. I found two smd A4 coded schottky diode were faulty: one is open(DD8) while other one leaky(DD3) (i.e voltage drop erratic).

So ordered for these diodes online and having received them I did the replacement.

See result after replacement below:

Read 459 Ohm from a 470 Ohm resistor (within 5% tolerance range)

This is the finished repaired work.

This article was prepared for you by Imoudu Onwumah from Nigeria. He is 62 years old and has just 3 years experience in electronics repairs. I started career in hotel industry as a chef, but then I was doing repairs only in electrical repairs as a hobbyist. In 2018, I decided to learn about electronics which through Jestine’s electronics e-books and holding my hand, am an electronics techie today.

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Note: You can read his previous article on Dead DVD Player Repaired

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Multimeter Repair

13 Comments

Tayo

January 28, 2022 at 8:59 pm

Another impressive repair Sir. Where those schottky diodes open, shorted or simple out of specs?

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Albert van Bemmelen

January 28, 2022 at 9:08 pm

The manufacturer probably didn't provide any schematic so it was good that you still could conclude they were schottky diodes from the A4 marking on top of them.

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GIFT ELIJAH

January 28, 2022 at 9:44 pm

That's a great work well done sir.

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Anwar Y Shiekh

January 28, 2022 at 10:40 pm

Most impressive work

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Waleed Rishmawi

January 28, 2022 at 10:50 pm

Why the seller did not take responsibility for the faulty meter. He was supposed to give you a new one and the faulty back to factory. I find that strange.
Any way good thing you repaired and got it over with , thanks for sharing

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Paris Azis

January 28, 2022 at 11:32 pm

Interesting repair. Nevertheless this instrument can measure up to 10mF, or else up to 10000μF and the capacitance measuring unit reference (Mega/Farad) in the text above is (practically) non existent.

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Gary Gemmell

January 29, 2022 at 12:23 am

well done

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Parasuraman S

January 29, 2022 at 12:37 am

First, the seller should have been pulled up for not honoring warranty. But the fix done by you is really great! One measuring instrument saved is equivalent to saving many! Good job there, dear!

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Yogesh Panchal

January 29, 2022 at 4:42 pm

Good Fix!

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moshe jacobson

January 29, 2022 at 9:30 pm

that was a heck of a good fix...really very impressive!

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Imoudu Onwumah

January 30, 2022 at 6:34 am

Thanks all for your comments. What does mF in capacitance stands for. Can someone explain this to me please. I'm learning.

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- Paris Azis
  
  February 1, 2022 at 8:03 pm
  
  One millifarad equals 1000 microfarad.
  
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Magsones'

January 31, 2022 at 6:06 pm

Great testimony!!!!

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