UT139E and UT139S Digital Multimeters - no discussion?

[Travie21]

Hello guys. Can I ask what's the problem of my meter? Its UT139E. I accidentaly plugged it on AC while its on resistance mode. I can still read low resistances from 1-1kohm I guess, but not be able to read over Mega Ohm. Continuity still works fine and diode test. The capacitance does not work, its stocked on 0.000 micro fara unlike before it starts on nano farad. Ac and DC voltage still works, but DCmV is on OL but indicating a high voltage on the corner of the meter. NCV does not also work now. I checked the board and see no burned or any signs of visual damage on the components. I also checked the fuses and still works fine. Hope you can help me guys.

[Fungus]

Hello guys. Can I ask what's the problem of my meter? Its UT139E. I accidentaly plugged it on AC while its on resistance mode. I can still read low resistances from 1-1kohm I guess, but not be able to read over Mega Ohm. Continuity still works fine and diode test. The capacitance does not work, its stocked on 0.000 micro fara unlike before it starts on nano farad. Ac and DC voltage still works, but DCmV is on OL but indicating a high voltage on the corner of the meter. NCV does not also work now.

Sounds like you zapped it.

I checked the board and see no burned or any signs of visual damage on the components. I also checked the fuses and still works fine. Hope you can help me guys.

Damage isn't always visible, fuses are only used on current ranges.

[HKJ]

A guess is that you have zapped the input protection transistor pairs. There can be a couple of these pairs.

[Fungus]

Today's lesson: Don't use non-CAT-rated muiltimeters on AC mains.

(in fact, don't use any multimeters on mains if you can avoid it, try plugging in in a lamp, they tell no lies)

This is a real man's mains tester:

[Hydrawerk]

Hello guys. Can I ask what's the problem of my meter? Its UT139E. I accidentaly plugged it on AC while its on resistance mode.

Was it 230VAC or 2000VAC from a microwave oven transformer??

[Travie21]

 Its a 230 VAC

[Travie21]

So theres no way in recovering my meter?

[HKJ]

So theres no way in recovering my meter?

Remove the protection transistors, if it works then, solder new protection transistor in.

[Travie21]

Btw my meter still works. But the resistance mode is unstable. It blinks from 0000 to OL. DCmV displays OL and a HighVoltage symbol pops. NCV and Capacitance does not also works. But anything else still works fine. Any guess?

[Fungus]

Btw my meter still works. But the resistance mode is unstable. It blinks from 0000 to OL. DCmV displays OL and a HighVoltage symbol pops. NCV and Capacitance does not also works.

Nice definition of "still works". 

So theres no way in recovering my meter?

Nobody knows for sure, we can't see it from here.

Any guess?

HKJs guess is the most likely but at the end of the day, things break. Learn from it and move on.

[Hydrawerk]

UT139E has some input protection, it should survive 230V, it is not much.
http://en.uni-trend.com.cn/index.php?m=content&c=index&a=show&catid=174&id=185
In the user manual, they say it has a 600V protection on all ranges. http://en.uni-trend.com.cn/uploadfile/2018/1129/20181129032713354.pdf

[Travie21]

So should I check the PTC?

[Fungus]

So should I check the PTC?

Yes!

[Travie21]

Should I desolder it first? Or I can test it while its on the circuit? Sorry, I'm just a noob in electronics

[Travie21]

May I know what kind of PTC are used on 139E?

[Travie21]

https://lygte-info.dk/review/DMMUNI-T%20UT139S%20UK.html

[daedalux]

WMZ12A

[paulbt]

Hello everyone !

I saw people are quite interested about this 139E/S series. I had a thought to buy the S one for a couple of weeks and I finally did it ! I made the purchase from TME last week and today I managed to open it's case and then do some basic tests.

First I want to show you some close-ups from the inside:

[paulbt]

...then I did some basic comparison measurements against a calibrated Agilent 34410A 6 1/2 digit bench multimeter.

On DCV it reads ~0,1% more than the Agilent. Example: 20,000xx V on Agilent and 20,02 V on UNI-T.

On Ohms scale it reads <1% both less and more than the Agilent, the biggest difference was seen on low value resistors (<60 ohms).

On uA and mA DC scales it reads identical with the Agilent, limited to the number of digits the UNI-T displayed. I tried random values from about 10uA to 500mA (with shorted PS).

On ADC scale it reads ~0,2% less than the Agilent. Here I tried values from tens of mA to about 3A (again with shorted PS).

On mV DC scale it reads almost identical with the Agilent, even if the voltage I was measuring was a bit jumpy (due to noise or PS ripple). You can see the head-to-head comparison in the videos below:

[paulbt]

Update !

Someone here asked about current consumption and battery life for the UT139S. Here are my results:

- at 3.2V supply (or 2x 1.6V full alkaline batteries) and high brightness display (default setting), it draws 19mA and with low brightness it draws 10mA.

- at 2.4V supply (or 1.2V per battery), the low battery indicator appears and it draws 30mA @ high brightness.

- below 2.22V it will beep, shutdown and continue beeping once every few seconds. Right before this happens, it draws 35mA.

The test was done using my Aim-TTi PL601 power supply and during this whole time I was measuring a random voltage and the reading was rock steady! 

More tests will follow up using a function generator (frequency, duty cycle, max/min recording). If you have any wishes/ideas for testing, please post them here.

   

[paulbt]

Hello,

I'm back with two interesting little tests. Please read the video descriptions.

[Fungus]

Hello,

I'm back with two interesting little tests. Please read the video descriptions.

Try getting some decent leads with sharp points. 

Limited bandwidth in AC mV mode. Not uncommon, I'm sure it's buried in the specs somwhere.

[Wytnucls]

Continuity test seems fine to me. Pretty fast and latched.
A lot of meters struggle with large DC offsets while measuring AC.

[paulbt]

@ Fungus

For first video: I tried many quality probes like agilent, fluke and brymen, but it does the same: beeping is not continuous when it should be. If I short the probes together the same thing happens...I'm pretty sure it's the meter...

For second video: There is only 100Hz, I don't think it's a matter of BW limit, more like a matter of DC offset. Please look careful what I'm trying to show in the video or read the description.

Overall, I'm aware that it is a mid-priced dmm and for sure you can't have the quality/functionality of a high-priced one.
I made those video just for info/review reasons.

[Fungus]

@ Fungus

For first video: I tried many quality probes like agilent, fluke and brymen, but it does the same: beeping is not continuous when it should be. If I short the probes together the same thing happens...I'm pretty sure it's the meter...

So why did you spend the entire video banging the probes around and poking at a PCB? Just short them. 

@ Fungus
For second video: There is only 100Hz, I don't think it's a matter of BW limit, more like a matter of DC offset. Please look careful what I'm trying to show in the video or read the description.

Description in thread is "Uni-T 139S bug".