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Old 05-11-2021, 11:13 PM   #1
PanicMechanic
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Default Extech EX330 multimeter current range offset fault

My multimeter has developed this fault, a few months ago. I tried to fix it, but had no success.

The fault is that on the current ranges it never shows 0. Does not matter if the probes are open or shorted.
As you can see from the pics, the offser is the same (just multiplied for other rages):

-4.9 uA
-0.49 mA
-0.49 A

I don't know what exactlly caused the fault.

The meter had a battery leak before I noticed the fault, but I am not sure if the fault was present before that happened. I just did not noticed. The battery leaked and coroded one of the spring contacts, and one of the solder joints for the battery wire on the PCB a bit. The battery was an expencive Varta with year 2025 exparation date, of course.

There have also been a few incidents over the years, of course. Like when I was checking the if the metal chandelier was grounded (using the resistance range), and the multimeter was showing weird readings and beeping. It turned out that the the chandelier has live with mains voltage. But the resistance range works fine.

Now, when I was trying to repair the meter a few months ago, I changed the Op-Amp TLC27M7. It had one of the higher input offset voltage versions (I don't remember which one exactlly), but I have changed it wit the 500uV offset version (the best one).
https://www.ti.com/lit/ds/symlink/tlc27m7.pdf

It did nothing.

The other chip is: https://www.onsemi.com/pdf/datasheet/mc14069ub-d.pdf
I did not change that.

Then I was cleaning the rotary switch contacts on the PCB and the switch itself, and it did show a change. I have cleaned it many times, and one time even managed to get it to show 0.02 or something, but by the time I have assembled the meter again, the fault returned. Then I tried cleaning it a few more times, without success. So, I have no idea...

Here I found the info on trimer pots: https://www.eevblog.com/forum/testge...-extech-ex330/
But none of them are for the current range.

I have tried to contact Extech to ask them for help. I used a business email, but they did not reply.


https://i.postimg.cc/28v10hnz/1.jpg

https://i.postimg.cc/V6d6nCYP/2.jpg

https://i.postimg.cc/d0QDQfp1/3.jpg

https://i.postimg.cc/52V6Tym8/4.jpg

https://i.postimg.cc/cLBrSW-D2/5.jpg

https://i.postimg.cc/CKv5RNp4/6.jpg

Last edited by PanicMechanic; 05-11-2021 at 11:20 PM..
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Old 05-12-2021, 12:01 AM   #2
PanicMechanic
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Default Re: Extech EX330 multimeter current range offset fault

OK, it is fixed.

I don't know what did it.

I reslodered all through-hole solder joints. Cleaned the PCB. Not tightened the 3 PCB screews all the way (before I had always tightened them all the way).

And it shows 00.00 now.
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Old 07-11-2021, 09:02 PM   #3
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Default Re: Extech EX330 multimeter current range offset fault

Can you give me the picture behind switch multimeter? Behind switch Off Vac Vdc Hz...
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Old 07-11-2021, 09:05 PM   #4
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Default Re: Extech EX330 multimeter current range offset fault

Quote:
Originally Posted by jinosean View Post
Can you give me the picture behind switch multimeter? Behind switch Off Vac Vdc Hz...
Is it like this my picture?
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Old 07-11-2021, 09:08 PM   #5
jinosean
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Default Re: Extech EX330 multimeter current range offset fault

Quote:
Originally Posted by jinosean View Post
Is it like this my picture?
please help me to solve this problem
Attached Images
File Type: jpg IMG20210712100406.jpg (465.7 KB, 16 views)
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Old 07-12-2021, 04:52 AM   #6
stj
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Default Re: Extech EX330 multimeter current range offset fault

is the problem that you dont know where the contacts go ?
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Old 07-12-2021, 07:40 AM   #7
PanicMechanic
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Default Re: Extech EX330 multimeter current range offset fault

Here you are:

https://drive.google.com/file/d/1Wk9...ew?usp=sharing

https://drive.google.com/file/d/1WlL...ew?usp=sharing


It seems that you are missing 2 contacts.
Or possibly you have a lower specification model that does not have those contacts, maybe?
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Old 07-12-2021, 07:46 AM   #8
jinosean
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Default Re: Extech EX330 multimeter current range offset fault

Quote:
Originally Posted by PanicMechanic View Post
Here you are:

https://drive.google.com/file/d/1Wk9...ew?usp=sharing

https://drive.google.com/file/d/1WlL...ew?usp=sharing


It seems that you are missing 2 contacts.
Or possibly you have a lower specification model that does not have those contacts, maybe?
ok, thankyou, I think i am missing 2 contacts
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