I screwed calibration in my UNI-T UT139C DMM - Page 1
Forum section: electronics / repair

author: Arek_R
author_rank: Regular Contributor
timestamp: May 20, 2018, 07:27:23 pm
content: Was trying to correct few mV error on 6V range.Hold RANGE + SELECT then turn on, RANGE to increase value and HOLD to decrease, SELECT to change parameter.Was thinking it will change it by 1 but it just went 100+, erasing previous value without way of recovering it, applying for example 2V makes it display 400 or something like that, doesnt make sense.Could someone please supply me calibration procedure?Also some time ago I toasted 1R resistor for mA/uA range, and in CAL menu there's no parameter for current calibration, how then I'm supposed to calibrate it?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 26, 2018, 02:22:04 am
content: What chip is in the 139C?You may find the calibration procedure in the datasheet.Edit: DTM0660 (@11:20 into this video:There is a partly translated datasheet of this thing on:http://www.kerrywong.comIt does not have the callibration procedure, but it does have a table of the callibration constants in the EEprom, you may be able to backup and manipulate those values with external means.(Can you easily put the DTM0660 in reset while reading / writing to the EEprom?)

author: stj
author_rank: Super Contributor
timestamp: May 26, 2018, 05:15:45 pm
content: kerry wong's translation is very incomplete.try this:

author: Arek_R
author_rank: Regular Contributor
timestamp: May 27, 2018, 12:25:43 am
content: Whoa thanks man!But omg this translation is painfull, will have to decode it...Oh wait so I have to short something inside?xD

author: stj
author_rank: Super Contributor
timestamp: May 27, 2018, 10:11:14 am
content: you should tweek it using an eeprom programmer.there is software on the russian forums.

author: floobydust
author_rank: Super Contributor
timestamp: May 27, 2018, 08:47:35 pm
content: There's a jumper required to disable write-protect on the EEPROM and enter CAL mode. So how are you upsetting calibration without that in place? A cold-boot of the meter should revert back to the original cal factors. Meter beeps once it saves to EEPROM. Unless you are removing the jumper after booting into cal mode- instead of at the very end.I tried to translate cal procedure here:https://www.eevblog.com/forum/testgear/cheap-aneng-meter-calibrationreset-procedure/msg1267492/#msg1267492

author: Arek_R
author_rank: Regular Contributor
timestamp: May 27, 2018, 11:25:45 pm
content: Thanks man, yours seem to be the clearest one.And you're right, how I messed the calibration without opening this and shorting J8 xD

author: daedalux
author_rank: Contributor
timestamp: March 19, 2019, 12:07:52 pm
content: I've also had the same problem. I don't know how it went out of calibration in first place. I examined the device and the pin required to short to ground to allow to calibrate the UT139E at least isn't even conected to anything. The multimeter will always start calibration turning on with select and hold pressed. I don't have a calibration bank but I tried to give it the calibration values as exactly as possibly could and it kept on measuring very odd. I even couldn't access some compensantions, like the high AC voltage, and high capacitance.If I understand the manual well, what is required is to give to it just 500mV, 500, 50K, 500nF and 50uF. It talks about some AC mode and high DC that I wasn't even able to trigger while fiddling. I even started to think that the internal voltage reference was unstable but with it open I didn't see any problem.Has anybody succesfully calibrated this device? Any help would be very welcome. I think that a lot of people is having this issue as this multimeter is very easily thrown into calibration mode by accident. Perhaps these compensations can be reset and the original calibration recovered as the pin to enable calibration has been left untouched?

author: Arek_R
author_rank: Regular Contributor
timestamp: April 03, 2019, 09:41:33 pm
content: Honestly I just gave up, it's too cheap to bother, now kinda feel bad for bothering people with this topic, sorry guys :/