Uni-T UT70D Multimeter Calibration

[cemelec]

I've search high and low for info on how to calibrate a UT70D multimeter, including these forums, no luck. It has been posted here before, but that was a few years ago.

Basically its an 80,000 count device, quite nice and capable of good precision  and it was spot on when I first got it maybe 6 or 7 years ago (Maplin). Now the voltage readings are significantly out and I'm hoping to fix it rather than put it in my junk pile.

I've totally disassembled it and there is not a single trimmer pot in sight, confirming the schematic (found in this forum)

I emailed Uni-T but as expected no response. There is no mention of it on their website, not even as discontinued, so they have probably totally abandoned it

Maybe its done via some key sequence?  Anyone have the remotest idea?

Thanks

[cemelec]

OK, I've abandoned all hope of getting support from Uni-T

Instead, and it works fine so far, is a bit of PCB trace cutting and substituting one of the resistors in the Vref path with a fixed resistor + trimmer pot. Now able to trim reading to match an external voltage reference, so I've rescued a fairly decent meter from the junk pile.

[MosherIV]

Normally you find a local company that specialises in calibrating test equipment/multimeters and get them to check calibdation and adjust if needed. The cal is then referenced to national standardsa and are traceable.

I have the B variant. There are 6 pots  inside for adjusting the calibration. I have never found the calibration procedure online.
However, most dmm calibration rarely drift. Mines has never drifted.

Some people disslike Uni-T because some models are very poor and their calibration does go after a while.