Troubleshooting Uni-T EEPROM ErrE

[DanFen]

I've got a UT139C that powers on for a second with an ErrE, before switching itself back off.

I haven't found much information about this, other then the error being caused by the EEPROM (both on the internet and from fellow members here). While I'm using a cheaper multimeter temporarily, I'm trying to troubleshoot this... hoping it won't go to trash

I've opened it up and did a visual inspection. Unfortunately I couldn't see anything obvious, everything looks clean and as new. No signs of damaged components.

I'm attaching two photos: one of the eeprom area, and the other I think are the rails on the back that end up to the eeprom (?). Also attaching datasheets.

And because I'm doing this to learn, and I'm still new to this, I have a couple questions.

1. What are the components starting with L? I know C are usually caps, while R are resistors, F fuses and so on.
2. Laugh at me, but, where do you find ground on these 2 layer boards? On laptops it's easy cause these are usually screw holes/ports etc.... What am I missing?

Thanks a lot

[lotas]

Re: Troubleshooting Uni-T EEPROM ErrE

Look here
https://www.eevblog.com/forum/testge...matics-avail)/

[stj]

Re: Troubleshooting Uni-T EEPROM ErrE

L are inductors.

do you have an eeprom programmer?

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

Thanks, will go through it.

Look here
https://www.eevblog.com/forum/testge...matics-avail)/

Hello again! Not yet, but on delivery. Went for the RT809F.

L are inductors.

do you have an eeprom programmer?

[lotas]

Re: Troubleshooting Uni-T EEPROM ErrE

Here are two original and modified firmwares for UT139C.

[stj]

Re: Troubleshooting Uni-T EEPROM ErrE

backup the original first, it has calibration data in it

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

I know it's been a while, but I just got to do this now. Wrote the shared bin to the IC, re-soldered it back, and still getting the same error :/

I also de-soldered the IC and read it again just to make sure that it got programmed correctly. Then compared it to the shared hex and they are the same... which concludes that the programming was fine.

[redwire]

Re: Troubleshooting Uni-T EEPROM ErrE

Post the EEPROM file you have, to see if it can be fixed.

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

This is the backup (the one I had before I wrote the shared one).

[stj]

Re: Troubleshooting Uni-T EEPROM ErrE

check the tracks between the eeprom and the main chip.
here is a schematic of another meter with the same chipset,
and a datasheet with example schem on page 17

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

Will try Is that done with the EEPROM back in circuit?

check the tracks between the eeprom and the main chip.
here is a schematic of another meter with the same chipset,
and a datasheet with example schem on page 17

[redwire]

Re: Troubleshooting Uni-T EEPROM ErrE

I looked at your EEPROM dump with a hex editor and did not see any errors. I can't know what every byte should be, but I did not see anything corrupt.
Check the EEPROM pullup resistors on SDA and SCL are OK, is R29 soldered on both sides? The main IC DTM0660 looks like solder balls are behind/under the pins?

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

Thanks for checking!

All resistors seem to be soldered fine, but I'll re-flow them just in case. I also measured them and the readings are good.

About the solder balls, do you mean in between pins? If so, it doesn't seem like it under the microscope, and I didn't reflow it or touch it in any way.

I also tested in continuity between the DTM0660 and the EEPROM IC, in case there's a broken trace, but all seems fine.

I looked at your EEPROM dump with a hex editor and did not see any errors. I can't know what every byte should be, but I did not see anything corrupt.
Check the EEPROM pullup resistors on SDA and SCL are OK, is R29 soldered on both sides? The main IC DTM0660 looks like solder balls are behind/under the pins?

[redwire]

Re: Troubleshooting Uni-T EEPROM ErrE

No, the solder bridges I see are UNDER the pins.
You can poke a wire or paper clip (gently) through and see if you hit them. Usually they are solder balls from extra paste and can poke out.

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

Doesn't seem to be the case, must be the quality of the previous photo

I'm still to re-flow the resistors around the EEPROM area.

No, the solder bridges I see are UNDER the pins.
You can poke a wire or paper clip (gently) through and see if you hit them. Usually they are solder balls from extra paste and can poke out.

[DanFen]

Re: Troubleshooting Uni-T EEPROM ErrE

Reflowed the resistors, still the same. While it seems to be interesting, I don't think it's worth working on it anymore. The only thing I miss about this is that it has auto range, and the other ones I have do not.

[stj]

Re: Troubleshooting Uni-T EEPROM ErrE

did you check the eeprom is getting power?

[redwire]

Re: Troubleshooting Uni-T EEPROM ErrE

For some reason EEPROM power has a R40 100Ω resistor to +V, and it's supposed to have a bypass cap 0.1uF across power and gnd but I don't see it.

[CapLeaker]

Re: Troubleshooting Uni-T EEPROM ErrE

Check with an oscilloscope the data line, clock and the main oscillator for activity.

[junphil]

Re: Troubleshooting Uni-T EEPROM ErrE

Please help....

Does anyone here have the working and original firmware of ut139???