Help fixing Digital Multimeter Proskit MT1210

[mikey5791]

Hi,
Yesterday i was using this dmm dc voltage 500v setting to check on a computer power supply by putting black negative probe to negative side of primary main cap and red positive probe to one of the diode cathode. I saw dmm reading briefly about 862dc; then a pop sound from my dmm. It is a huge mistake, i should have put the negative probe to cold ground.
Now this dmm can no longer check dc voltage. I opened the dmm case but found the fuse still good continuity test with my analog multimeter. No burnt smell or exploded parts from the inside.
Hope anyone reading this can help me fix the digital multimeter as this is the only digital set i have. Thank you.

 

[mikey5791]

Hi,
I wish to upload photos in jpg format, size of 1.85MB each. How can i do this?

 

[(*steve*)]

First step is to open it up and check out all the burnt stuff.

To upload a large image, use an image compression tool like tinyjpg.com to make it smaller

 

[pharaon]

I wish to upload photos in jpg format, size of 1.85MB each. How can i do this?

my favorite website to host images

 

[(*steve*)]

my favorite website to host images

That's actually a horrible solution because the images can disappear rendering threads useless in the future.

 

[mikey5791]

Hi,
Attached two images of Proskit dmm front and back. (Thanks to steve for tip on the tinyjpg.com)
Upon opening the inside case, i noticed one resistor (blue,black,black,black,brown) at R27 paint little chip off. Measuring ohm using my analog multimeter shows no reading. Is this 5 band resistor a smd type 600ohm?
I am ordering a new digita type dmm online and expect to get in

 

[(*steve*)]

R28 seems to have the same value, measure both of them.

The paint chip probably blew off when the resistive trace vaporized under it.

There doesn't seem to be much input protection on this multimeter, so the damage may not be limited to the obvious.

 

[mikey5791]

Hi,
Thanks for reply.
Once i received my new dmm, I will measure both R27 and R28, and the rest of every visible parts that could
have damaged. However, i guess this will take until end of this month or later due to shipment affected by the global
pandemic.

 

[mikey5791]

Hi,
Just for inquiry. If resistor at R27 is damaged, which type of my stock resistor can be used as replacement?
Attached image of my stock resistors. Appreciate your advise.

 

[pharaon]

well you can see the colors of the original and find out it's value the same way " that's why they put colors on resistors " and then replace it with the same value resistor

 

[mikey5791]

Hi,
Received my dmm yesterday and do measurement on resistor R27(reads 1) while R28 reads 882 ohm. It looks like R27 need replacement. Is R27 a 600ohm 5 band type resistor? Can i replace it with a 600ohm 4 band resistor instead?
The rest of the resistors measured within their own spec except one resistor on lower left part color of green,silver,white,white,black. From 5 band resistor calculator, it is a 58.9G type. Sorry i am clueless on this. So I use my dmm largest resistance scale at 200M and it reads 0.8. Anyone can help me on this 0.8 reading and is this a correct reading for the 58.9G resistor? Appreciate any response and suggestions on making this dmm to work again.

 

[(*steve*)]

I doubt that resistor is 59.8G. leave this alone for the moment.

I would advise that you replace the open 600 ohm resistor. You probably won't find a 600 ohm replacement, 560 ohms will be close enough to see if it's the extent of your problems.

The 600 ohm resistor that is reading high should also be removed (or one lead lifted) and measured again. It may also need replacement.

 

[mikey5791]

Hi,
I replaced the open 600ohm resistor with a 680ohm, the nearest ohm i can find. The dmm works now (but negative display on standby), while measurement on dc volt a bit off. I measured a used cr2032( 3 volt battery) the dmm reads 3.11volt.
Is there any way i can calibrate and do manual adjustment? I saw there is an adjustable white blue varistor marking 102 inside the board but not sure how to adjust it. Can you help me on this?

 

[(*steve*)]

WOW! You are indeed lucky that those resistors took the brunt of the overload.

Since the 680 ohm resistor(s?) got it in the ballpark, now it's the time to get some precision 600 ohm resistors.

If you're in the US I would recommend digikey. Something like this would probably be ok.

 

[mimsanere]

Hi,
Attached two images of Proskit dmm front and back. (Thanks to steve for tip on the tinyjpg.com)
Upon opening the inside case, i noticed one resistor (blue,black,black,black,brown) at R27 paint little chip off. Measuring ohm using my analog multimeter shows no reading. Is this 5 band resistor a smd type 600ohm?
I am ordering a new digita type dmm online and expect to get in

What is resistor number R26?