UNI-T UT61E Multimeter teardown photos.

[honeybadger]

joeqsmith: in ES51922 datasheet there is:
Most of pins are protected by the ESD protection circuits. However pins, V+, V-, AGND, DGND and
VR1 are not protected enough because the parasitic effect must be decrease. Therefore enough external
protection is needed for assembling, carrying and keeping. In addition, components connecting to these
unprotected pins have to be soldered on board before the IC is soldered.

I just wonder. There is no PTC... nothing. When the 10M resistor fails (or more probably any of the capacitors around) the current will go straight to the IC.

[joeqsmith]

joeqsmith: in ES51922 datasheet there is:
Most of pins are protected by the ESD protection circuits. However pins, V+, V-, AGND, DGND and
VR1 are not protected enough because the parasitic effect must be decrease. Therefore enough external
protection is needed for assembling, carrying and keeping. In addition, components connecting to these
unprotected pins have to be soldered on board before the IC is soldered.

I just wonder. There is no PTC... nothing. When the 10M resistor fails (or more probably any of the capacitors around) the current will go straight to the IC.

That's a VERY good point.  Consider that for DC the capacitors are an open.  Apply a fast transient, like ESD, and they will pass it right on through.   In this case, adding the MOVs won't help.  They may have a fair amount of capacitance but the inductance seems to dominate at these higher frequencies.  No real surprise.   

The PTCs and surge rated resistors are there to limit the current through the clamps.  The problem I see with the 5mm parts is they will break down.   

I made a video some time ago showing all of this on the 61E which includes the part of the document you posted.   I basically walked through the problems and explained a few ways to attempt to improve it.   Sadly, most viewers had little interest in the theory.   I've added a link.

https://youtu.be/cMutvk_6xhY?list=PLZSS2ajxhiQDrk4o1Y45auwK7LomjnNBU

[DiddlyJackSquat]

If anyone has been chasing my thread about my faulty UT61E here's the gist...
Have issues with it powering on but no beep and the screen goes blank?
reflow the IC and it is revived momentarily?
Check the ecaps on the other side of the board (the battery side) for leakage or... just replace them. piece of crap leaked a little. can't imagine what would have happened if i saw it later. I replaced them with through hole in a method I call "through hole surface mount soldering"
while you're there, replace the solder on the 3.999 oscillator because that lil butt solder cracked on mine!

chasing red herrings all day long 

[honeybadger]

Hi, my new UT61e just arrived and I must say I am confused about voltage ranges.

at "mV" DC range it says "OL" when nothing is connected.
at "mV" DC range it measure "0.20mV" even with terminals shorted with thick wire with gold plated banana plugs.
at "V" DC range it masure "0.0020V" with shorted terminals.

This shouldn't be happening I guess. With all my others DMMs when voltage is selected and nothing is connected it shows something but definitely not "OL" and when I short the terminals it shows something really close to zero - definitely not 20 digits above zero.

Is this enough for a warranty claim?

edit: accuracy is suppose to be:
220mV +/- (0.1%+5)
2.2V / 22V / 220V +/- (0.1%+2)

So for 220mV range it is suppose to show 0.05mV in worst case scenario -> offset is 400% off.
For 2.2 range it is suppose to show 0.0002 in worst case scenario -> offset is 1000% off.

edit 2:
It measures off by 0.4V at 30V DC. Jesus Christ how is this possible with a new multimeter?  5USD noname is more accurate.

Update:

After collecting dust for several months I finally decided to try the ultrasonic cleaner. I had an idea that there must be some leakage current somewhere to cause the offset.

After 10 minutes in ultrasound and drying with a hot air gun  and adjusting VR1 it works like a charm!
DC voltage 0.1-30V there is a next to nothing difference to BM867s - definitely less than 0,5%, good enough.
DC current - OK.
Cap - OK.
Res - OK.
mV range will still show "OL" when not connected, but "0.00" when shorted - probably OK.

I am surprised that trimmer pots survive ultrasound without any problems.

[tecnicaemail]

Hey guys, first of all I'm sorry for my English, I'm using Google Translate, today my UNIT UT61E arrived, after some research I saw that many people recommend that I put photos of it open for you to see if something has changed since 2020?  I read the 45 pages of the topic and found it interesting to put the led to light the display using the HOLD button but I was in doubt, can I ask right here?  I thank everyone.

[tecnicaemail]

Friends follows pictures of the disassembled multimeter.

































I took several photos to be able to see clearly.

There are some spots that seem to have oxidation should I clean?

I circulated in white, where it appears to be oxidation!

I thank everyone.

[Fungus]

There are some spots that seem to have oxidation should I clean?

I circulated in white, where it appears to be oxidation!

That's flux residue. It looks like some things have been soldered and/or retouched by hand.

It's probably not important but you might as well clean it next time you take it apart.

Fuses look OK - much better than the glass fuses found inside some of these meters.

There's still some missing safety components though. All the squares labelled "SG" should have a Spark Gap (or maybe a MOV) in them.

[tecnicaemail]

There are some spots that seem to have oxidation should I clean?

I circulated in white, where it appears to be oxidation!

That's flux residue. It looks like some things have been soldered and/or retouched by hand.

It's probably not important but you might as well clean it next time you take it apart.

Fuses look OK - much better than the glass fuses found inside some of these meters.

There's still some missing safety components though. All the squares labelled "SG" should have a Spark Gap (or maybe a MOV) in them.

Thanks for the reply friend, taking advantage and abusing your knowledge I have the opportunity to exchange this Unit UT61E for a UT532 do you think the exchange is viable? Because I noticed that UT532 does not measure Amperage in microamperage and I am in doubt if its capacitance is good to measure, could you give me your opinion? I am grateful, thank you.

[myf]

Hello,

I have now 2 ut-61e. And I won't switch to any other multimeter (in this price range).

Indeed, first it's a 20000 count DMM. Of course it's not a precise 20000 counts. But 20000-counts multimeter is more precise than a 2000-counts multimeter and avoid switching range for a 10 times larger measure, or a 10 times smaller measure.

Second the usb-link from ut-61 to laptop is around 10eur and is very conveniant. There are very few with this possibility, at this price with its insulated link.

I test several claimed 0.01% resistors bought on ebay (but I'm not sure, it seems it was an old stock with unknown history). With 3 resistors, series connections and/or parallels connections every time 5 counts were missing : 9995 and not 10k, 19995, 4995, etc. There was about +/-1 or 2 count difference between the 2 multimeters. Theses errors seem to proof a light multimeter error, not an error of resistor value, but I don't have others material nor idea to proof this.

min/max switch on ut-61e is powerful : It actually the peak value during a very very short time (maybe 1ms or less),  not the extreme values read on the multimeter : a mean on 0.5 second.     

It seems that ut-71 is more expensive and older than the ut-61. Temperature measures seems the only missing tips on this ut-61e.

Hope this help you to choose !

F.

[indman]

I test several claimed 0.01% resistors bought on ebay (but I'm not sure, it seems it was an old stock with unknown history). With 3 resistors, series connections and/or parallels connections every time 5 counts were missing : 9995 and not 10k, 19995, 4995, etc. There was about +/-1 or 2 count difference between the 2 multimeters. Theses errors seem to proof a light multimeter error, not an error of resistor value, but I don't have others material nor idea to proof this.

UT-61E has low linearity of resistance measurements even in comparison with simpler Chinese models.
Here is a simple experiment that anyone can repeat.
I took 4 resistors C2-13 0.25 0.1%:
1.1kΩ
2.1kΩ
3.2kΩ
4.1.3kΩ
You can see the result of the sum of resistances on the display of each multimeter. And I wrote the results of measurements of each resistor separately in brackets.
In the photo there are 4 devices with the results of measuring this chain of resistors:
1.UT61E (0.995 + 0.995 + 1.992 + 1.294 = 5.276) - difference 13 ohms
2. Aneng Q1 (0.999 + 0.999 + 1.997 + 1.299 = 5.294) -  difference 4 ohms
3. Aneng AN302 (1.000 + 1.000 + 1.998 + 1.300 = 5.298) - difference 0 Ohm
4. Victor VC921 (1.001 + 1.002 + 2.001 + 1.302 = 5.306) - difference 1 Ohm

[Mickle T.]

UT61E has one of the best resistance measurement linearity among mid-range handheld multimeters.
These results was obtained by use of precision impedance synthesizer with a 2 ppm linearity error.

[tecnicaemail]

UT61E has one of the best resistance measurement linearity among mid-range handheld multimeters.
These results was obtained by use of precision impedance synthesizer with a 2 ppm linearity error.

So between U532 and U61E, better to stick with 61?

[indman]

UT61E has one of the best resistance measurement linearity among mid-range handheld multimeters.

How can you explain the results of my simple measurement? I still trust my eyes and tools.
Are these your graphs and conclusions?
https://vrtp.ru/index.php?showtopic=28912&view=findpost&p=788126

[Mickle T.]

My explain is very simple: UT61E is the best among chinese DMMs and is worst, compared to all other DMMs in my lab 

[Fungus]

How can you explain the results of my simple measurement? I still trust my eyes and tools.

maybe you got a bad one.

(and that is the main problem with Uni-T meters - you never know what's inside one)

[indman]

maybe you got a bad one.

No, I have the same UT61E as the majority of users. 
If you look closely at the table with the results Mickle T., the link to which I indicated above, you will see that in his UT61E in the same experiment with 4 resistors, at the 22kΩ limit, the deviation from the theoretical value was 12Ω.
The UT61E is a good instrument for its price category, but if I need to accurately measure some kind of resistance, I entrust this work to other instruments that have digital calibration on each measurement range.

[Fungus]

If you look closely at the table with the results Mickle T., the link to which I indicated above, you will see that in his UT61E in the same experiment with 4 resistors, at the 22kΩ limit, the deviation from the theoretical value was 12Ω.

OK, but the whole "adding resistors together" is surely a red herring. The problem is more likely that you're at 22 kOhms on a 22000 count meter.

Maybe the auto-ranging is freaking out internally. What happens if you lock the range manually?

Even if it stays the same: You're still on the limits of the ADC and still easily inside the 0.5% spec of the meter.

[myf]

Hello everybody,
and excuse my poor English for these very interesting posts.

a 22000 count meter is at full scale for a (little less) than 22Kohm resistor.   
Fungus do you explain that at this full scale, ADC have a more important relative error (in percent) ?
Where is the best range ? With this ut61e I often measure 0 count for a very low 5 count (over 22000) real value.

Can we model : "a more precise (or real) value" = "a fixed offset count" + "a rate around 1 as 0.995 or 1.005 " * the measured value ?

Indman results are interesting, I got about same values with my tests.
Can we detect what is the error of each measure ? Of course all these values are inside the assumed error rate for this multimeter.

On the other hand an offset error = + 4 counts improve these set of measures.  This is the opinion of the mathematician, not that of a physicist.
In this case, the measurements are almost perfect at +/- 1 unit. What is your advice?

I don't have neither precise resistors (but 10Kohm maybe at 0.01%) neither 5.5 or more digits multimeter.
I have a set of 1% (or 5%) standard resistors.     

Suppose you establish a serial link with 20 resistors: each resistance = 100 ohms and 1% error. Then I measure AND each resistor, AND all of those partial links of 1, 2, 3, ... 20 resistors. So I can build the table of "X = sum of measured resistances" (= 98 + 101 + 99 for example) and "Y = measured value" (= 398 in this case).
What information can I get from this graph? Of course, I don't know if the error is "inside each resistor" or "in the multimeter" !

What (other) simple and common tests are possible with one or two multimeters?

F. from France.

[rsjsouza]

UT61E has one of the best resistance measurement linearity among mid-range handheld multimeters.
These results was obtained by use of precision impedance synthesizer with a 2 ppm linearity error.

So between U532 and U61E, better to stick with 61?

tecnicaemail, I looked at the UT532 and it is an insulation meter as well as a multimeter without the A range. Considering this, the UT61E is a better general purpose multimeter, while the UT532 has a very specialized function.

The choice depends on what you already have and what you do. If you have other multimeters and the UT61E is just one more, then the UT532 has a unique function that may be interesting to have in case you need it. Otherwise, I would choose the UT61E as it has more useful features.

[Lenny]

I also have the UT61 multimeter. 
Unfortunately, the automatic range selection does not work when measuring resistance.

All values are displayed in the megohm range.
Even with small resistances, the device no longer switches into the small ohm or kilo-ohm range.

If I turn the function selector with a resistor already connected, e.g. from volts to ohms, the correct range is displayed.
Switched to the manual mode, I can only switch from Ohm -> kOhm -> MOhm, but not back. It stucks in MOhm

Has somebody an idea?

[Fungus]

I also have the UT61 multimeter. 
Unfortunately, the automatic range selection does not work when measuring resistance.

Has somebody an idea?

Time to buy a new one.

[Losreelos]

hello
where can i download the diagram? I'm looking for the one from UT61B
regards

[ovidiu_vr]

My own multimeter UT61E has a resistance RA of 1.68kΩ, is written 103 , which means 10kΩ, the lenght it is ~ 2mm. I will remove it and measure it to see how much it has. The PCB has marked with 150507-9C 61E KS-01 94VO E210448 1649 P2G04445 SC6

[ovidiu_vr]

I desoldered the resistor and I confirm that RA has 10.1k (103), the length it is 1.5mm and the case 0603(inch) or 1608 (mm).

[Gyro]

I can't see resistor "RA", maybe you can highlight it on an image.

Some resistors have fine trim resistors associated with them... for instance R7 has R7A. These trim resistors will naturally be different values according to the actual value (within its tolerance range) of the main reistor, measured at the factory.

If your "RA" is one of these, they you should leave it alone.

Is your meter not working in some way?