UNI-T UT61E Won't hold calibration

[Danielfs78]

Hi,

First of all, forgive my English, i'm not a native speaker.

I'm starting to play with electronics (mostly arduino stuff) as a hobby, and i have an UT61E, bought a couple of years ago that just started reading lower voltage values.

I almost have no free time nowadays, so since i bought it i must have used it no more than 50 times or so. It justs sits on my bench.

Recently, i was building another variable power supply and the 61E was reading about half volt lower than the 5 volts the PSU was outputting. I thought that the PSU was falty, but the next day i tried my old, cheap multimeter and the PSU was spot on.

Since then i did more tests (with a new battery, other multimeters and a chinese voltage reference) and the 61E was the problem.
The problem also occur when measuring AC voltages, what supposed to be 126V was reading 106V.

I read about calibrating it and i did. It needed only a tiny movement on VR1 to fix DC and AC measurings (i did not try the rest of it's functions).
For a few moments it was right again, but the next morning the error showed up again, and that's about the same offset as before.

Does anyone knows what i should do to fix it?
I read about checking the resistor array or replacing the voltage reference, but could not find anything i could follow.

Thank you all in advance.

Daniel

[rsjsouza]

Olá Daniel, I think in your case it will be better to replace the multiturn trimmer with a better quality one.

There is a thread where people discuss replacing it, check it out:
https://www.eevblog.com/forum/testgear/replace-dc-calibration-potentiometer-on-ut61e/

[Danielfs78]

Thank you very much!

I'll try that!

[newbrain]

This is what happened to my UNI-T 61D.
The 61E schematics shows a single resistor while the 61D had four, but the symptoms are similar: worth a check.

[rsjsouza]

This is what happened to my UNI-T 61D.
The 61E schematics shows a single resistor while the 61D had four, but the symptoms are similar: worth a check.

Thanks for sharing this. Yes, the UT-61E has a single large resistor network as the divider. If that goes bad, a full replacement will be needed (although I fixed a 8060A years ago that had a bad joint between the PCB pin and the pad on the network itself). 

In the OP's case, though, it seems the pot went bad - a light touch on it seems to bring the meter back to the correct measurement. That or a resistor is constantly drifting...

[Danielfs78]

Thank you very much!

I'm having trouble trying to understand how you got to the R24C resistor from that datasheet image, as in the image it's labeled as R31...

I'm trying to look for the single resistor on the UT61E but the only part that makes sense to me is where the VR1 pot is, and it appears to be part of a voltage divider with two more resistors.
I just cannot find that single one that you said.

Can you point it to me, or even better, explain to me how to find it?

Again, thank you very much!

[modz786]

Heads up people with a UT61D the voltage DC is adjusted with VR4   ...Corrected on 5 nov typo I wrongly entered VR2, it is VR4