Multimeter Uni-T UT61E Problem (Solved) - Page 1
Forum section: electronics / repair

author: ptluis
author_rank: Frequent Contributor
timestamp: March 31, 2021, 12:27:48 pm
content: Solved, see my last postHi guysThis problem started to happen a few days ago. I have a problem with the UT61e multimeter making measurements in the volts mode. The measurement of any DC or AC voltage (auto mode is slower or manual mode) takes about 3-5 minutes to stabilize and display the real voltage value. For example measuring a 9v battery, measurement starts at 9.53v and goes down slowly (3-5 minutes depending on room temperature) until it reaches the stable value of 9.32v which is the real value compared to other multimeters. This problem occurs when I start the multimeter for the first time and only after 10-15 minutes of keeping the multimeter on, the measurements are fast and normal within 1-2 seconds. The rest of the multimeter's functions work perfectly by measuring correctly and within 1-2 seconds. This is annoying because if I want to make a quick measurement from off position, I cannot get a stable value right away. This multimeter is only used for low voltage readings.Things I've done without success:- I turned off RS232 because the readings were even slower, about 2 minutes more- Cleaning the entire flux on the pcb- Switch cleaning- I cleaned flux from the main chip ES51922 (improved a little)- I tested the related components according to the schematics and did not detect any problems.- New battery- Check/tested voltage trimpot- (update) Resolder all pins of ES51922- (update) Try to find overheating capacitors or other components, none detected- (update) Inspect all pcb soldering with optical stereo microscopeI suspect that the ES51922 chip will be defective because after 10-15 minutes on, the measurements work perfectly. I noticed that the ES51922 chip is warm after 10-15 minutes on. when warm works well, cold does not.If it is the ES51922 chip, I start thinking about buying another multimeter, but certainly won't be Uni-T, maybe an owon B41T + but I have to read reviews first. The price of an ES51922 chip costs almost as much as the multimeter.Does anyone have an idea of ​​what it might be?

author: rsjsouza
author_rank: Super Contributor
timestamp: March 31, 2021, 01:34:20 pm
content: Indeed it seems you did a lot already. One last thing I would do is retouch the solder on its pads - maybe some cold joint is getting in the way of proper work.I would perhaps do this only after buying another meter, so I wouldn't be stuck.I don't know what is available in Portugal, but some cheaper and interesting options to the Owon are the Zotek ZT-219 (also Aneng AN870, Richmeters RM219) or the newer Zotek ZTY (also Bside ZT-Y, Richmeters RM777, Aneng SZ18)https://zotektools.com/products/I did some tests on my channel (in portuguese) of both theRM219and the first impressions of theZT-Y.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 01:48:47 pm
content: QuoteIt should not become warm since its current consumption should be only 2mA. Not necessarily failure of IC itself, might be some surrounding component, like shorted MLCC.

author: PKTKS
author_rank: Super Contributor
timestamp: March 31, 2021, 02:04:01 pm
content: true.. try the alcohol method to spot the hottest component..or petrol or IPA...Careful inspection of the evaporation will tell you the most likely culpritIf the main chip... it really costs almost a brand new onePaul

author: ptluis
author_rank: Frequent Contributor
timestamp: March 31, 2021, 03:29:58 pm
content: Quote from: rsjsouza on March 31, 2021, 01:34:20 pmHi thank you for your answer. I indeed resolder all chip pins, forgot to mention that above. Didn't solve. Then inspect them and all other components on the pcb with a stereo optical microscope.I'm looking for a 22000 count or better. I think the models you mention are 19999 count but I will consider them if price is good. Normally I won't buy equipment in Portugal due to inflated prices, prefer to order from other EU coutries or China even if they came with 1 year warranty.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 03:33:37 pm
content: You first need to check its current consumption. When you see IC becoming warm, blindly reordering all of its pins is not the smartest idea.

author: ptluis
author_rank: Frequent Contributor
timestamp: March 31, 2021, 03:44:13 pm
content: Quote from: wraper on March 31, 2021, 03:33:37 pmI updated list of tasks I've already done. The only component heating is the main chip. I resolder all pins of the ES51922 using a stereo microscope and 45x zoom to make sure they are perfect soldered. I'm thinking of removing the chip and inspect the pcb under it, but only when I get my hands stable again.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 03:48:24 pm
content: Quote from: ptluis on March 31, 2021, 03:44:13 pmYet you don't have any actual measurement figures, only subjective "feel". IC heating does not mean that IC is necessarily problematic. Some part may be shorting one of IC pins, thus drawing current and causing it to heat up.

author: ptluis
author_rank: Frequent Contributor
timestamp: March 31, 2021, 04:14:55 pm
content: Quote from: wraper on March 31, 2021, 03:48:24 pmHi thank you for your answer. what would be the proper way of testing this chip without lifting the pins or cutting the tracks? btw do you know what is the normal consumption of the multimeter turned on? The chip you already said it was about 2ma in your previous post.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 08:03:19 pm
content: I don't think the rest consumes much more than this IC. Likely less than 5mA. Even 10mA won't make IC noticeably warm, so current should be quite significant.

author: ptluis
author_rank: Frequent Contributor
timestamp: March 31, 2021, 10:15:41 pm
content: Quote from: wraper on March 31, 2021, 08:03:19 pmToday the meter works just fineI measured the consumption of the multimeter and it's 4.7maI thought about what changed between yesterday and today and it was the outside temperatureToday the ambient temperature is +22º Celsius and the meter works well. Yesterday it was +17º and measure poorly.So I decided to do the experiment by placing the meter in a box and then lowered the interior temperature below + 18º, I waited a few minutes to stabilize the temperature and ... the meter started to measure poorly againThen I increased the temperature to + 22º and let it stabilize for a few minutes and the meter works perfectly!So seems temperature related??? When the meter measure ok the ES51922 chip stay cold, when measure poorly the chip stay warmI really don't understand what's going on hereedit: I forgot to mention that the multimeter consumption when measure poorly is 18-19ma

author: rsjsouza
author_rank: Super Contributor
timestamp: March 31, 2021, 10:33:19 pm
content: This is probably on the board - either a track, an inner layer or a via that is acting up.It is definitely temperature related - the minute difference is enough to trigger this issue.I would cool the DMM and warm specific parts using a hot air station that can blow a very narrow hot air stream.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 11:25:05 pm
content: Might be bad MLCC. When they become shorted, often short disappears at higher temperature. Or something may be oscillating at lower temperature.

author: wraper
author_rank: Unknown
timestamp: March 31, 2021, 11:57:13 pm
content: Check voltage regulator W1, something might be going funny with its 3V output voltage.https://ibb.co/Wvn5myS

author: ptluis
author_rank: Frequent Contributor
timestamp: April 01, 2021, 12:00:43 am
content: I measured the resistance between the ground pins or ground connections on the chip side, pins 3, 4, 5, 28, 116 and the results are not zero, some with 0.02 ohms (pins 3-5), others with 0.04 ohms (pins 3-4). I'm using thin gold-plated multimeter wires. Is it possible that these small differences could somehow cause the multimeter to measure poorly? Another thing I'm thinking about is a pcb defect like rsjsouza mention, but it looks like it could be the tracks below the chip, so I need to remove it to check, and this is an operation I can't do at the moment. A defect in the pcb tracks could explain the increase in current and the heating of the main chip or am I thinking wrong?Edit: between COM and pins also non zero, 0.05 ohms for pin 3, 0.08 ohms for pin 4 and 0.06 ohms pin 5

author: ptluis
author_rank: Frequent Contributor
timestamp: April 01, 2021, 12:07:44 am
content: Quote from: wraper on March 31, 2021, 11:25:05 pmI Will check that maybe apply some heat and cold to better test them, haven't do that yetQuotemeasured on output pin = 3.26 V (bellow or above ambient temp of +22º )

author: wraper
author_rank: Unknown
timestamp: April 01, 2021, 12:14:17 am
content: It should be 3.0V if Vreg is as on the schematic. It could be normal only is 3.3V Vreg is used instead.

author: ptluis
author_rank: Frequent Contributor
timestamp: April 01, 2021, 12:38:32 am
content: Quote from: wraper on April 01, 2021, 12:14:17 amCan't say for sure what is this chip, there is no markings

author: ptluis
author_rank: Frequent Contributor
timestamp: April 01, 2021, 11:02:50 pm
content: Problem solved for now.I don't know exactly what was the problem, but I start thinking that since it was malfunctioning below a certain temperature it could be something related with moisture, so I place the PCB in the oven for 1 hour at 50º celsius. Now the multimeter work perfect down to 0º celsiusNote: first I remove all parts that could melt.will it last? I don't know but it's working. I didn't notice any deviation in calibration. All functions work fine.I also did a "mod" that made the multimeter to be less affected by external temperature and readings are now faster. I cover the "resistor bridge" (don't remember what's the English name), it's the black rectangle, with aluminium tape, and this makes the multimeter much more stable and unaffected by external temperature. On some models this "bridge" is shielded, on mine there's no shield.Thank you all for you help!