Uni-T UT139C EEPROM Repair

[hexaglow]

I recently attempted to use my UT139C, only to discover it had bricked itself since the last time I used it. Switching it on flashes 'ErrE' on the display briefly, after which it switches off. Some googling has revealed that this indicates an error reading the EEPROM. It was working fine last time I used it, so I guess the chip has gone bad.

I am considering buying a replacement EEPROM chip and soldering it onto the board. However, since mine has died I don't have the correct data to program onto it. On another forum topic (https://www.eevblog.com/forum/testgear/uni-t-ut139c-lcd-biasing-(schematics-avail)/) I saw some people posted the contents of their EEPROM. However, if I understand correctly, the data contains some (unit-specific) calibration data, so there's potential for incorrect readings if I just use someone else's.

Obviously there's not much point in owning an inaccurate meter, so does anyone know if it's possible to recalibrate myself and get good results? If not I will have to buy another meter (probably from a different brand, given that this unit isn't very old nor heavily used).

[RayRay]

I disagree with your diagnosis. Even if the message shown is related to an eeprom reading issue, it's far more likely to be caused by one or more faulty components than a faulty eeprom chip and/or corrupted eeprom data. Open it up and start with a visual inspection,see if anythings stands out, if not, then check the components. On a side note though, I have the same meter myself (for over 5 years now, as well as other UNI-T meters) and I completely disagree with your sentiments on their reliability. UNI-T is definitely a reliable brand (You sure you haven't misused it somehow?) Anyways, you should definitely have more than one meter, and this also applies to any item which you consider important or use on a regular basis, exactly for cases like this (if you have only a single meter which goes bad, then the inbetween time til you repair or replace it is a bitch, plus repairing it by itself would often require another meter!) Also, if you get a new one, I highly recomment the UT191T

[hexaglow]

Hi RayRay,

Thanks for your suggestions. I can't recall any event that could have damaged it. I have never dropped it or exposed it to excessive voltage or current. Last time I used it, it was working perfectly. I was very happy with the meter. I put it in a box for a few months. When I tried to use it yesterday, the error occurred. I thought it might be a battery problem, so I swapped in some fresh alkalines, but it didn't help.

I have disassembled the unit and inspected the PCB with a loupe. I did not see any signs of corrosion, cracking or damaged components. Visually, it is in very good condition. My inclination would be to check continuity between the EEPROM and the main IC, but as you noted, I can't do that without another multimeter. I swear I had one of those pocket multimeters too, but I can't seem to find it...

So I am going to have to get a new meter anyway. I had a look at the UT191T, but I couldn't find any stock in the UK so I would have to wait a long time for that one. Also, I am planning to spend more time on electronics, so I am considering meters at a higher price point. I have been looking at the Brymen BM235. I am open to suggestions in the ~£100 range (inc VAT).

[perieanuo]

I am open to suggestions in the ~£100 range (inc VAT).

in this range, buy something serious fluke chauvin-arnoux ...i found at 90 euros some perfect C.A 5275
you will avoid EEPERROR and stuff like this, the measuring will do fine, robust...it will last for decades
my fluke 110 don't wanna die whatever i do like putting 220V on resistance selector 
recal at least for voltage, if instrument allows calibrating only V part, cost nothing with those 10V precision modules from china and some precision resistors to divide the 10V to what you cal needs