UNI-T UT33D very low-cost multimeter: Teardown and review

[ciccio]

Some time ago I had my car visited by thieves, who took away my tool bag.
I had another empty bag, but had to buy new tools and new test instruments, and I decided to go, where possible, for the lowest cost way.
Instead of another FLUKE 117 (that was too much for the actual use) I bought this UNI-T UT33D multimeter for the very cheap price of 11 Euros, from a distributor that maybe wanted to empty his stock, and I discovered that, even with the annoyances that I will write about later, it was usable.
You can find  the specs on the UNI-T site : http://www.uni-trend.com/UT33D.html

Now the Blog is full of reviews of multimeter of high quality , but I though that the teardown of a very  low-price unit  could be interesting, and I dedicated this Sunday afternoon to it..
Please forgive me for the length of this posts: as my age increases, I'm becoming more prosaic…

The unit comes in a nice cardboard box, with a simple (too simple) instruction manual (two A4 pages valid for the whole UT33 range (3 models), and a couple of probes.
Basically, it is a small size, manual ranging, 3 ½ digits multimeter, labeled CATI to 600V and CATII to 300V,  with scales from  200 mV to 500V DC, 200 and 500 V AC, 2000UA to 10 A DC, 200 ohm to 200 Mohm, diode and continuity test, and a very unusual 50 Hz square wave output.
The display is a very readable 13 mm LCD,  with green LED's retro lighting.
Probes are of medium quality, labeled 10A, CATII 600V, but the tips are not so sharp as they should be and the points are not insulated, but they survived a "flex test" of cable junctions.
There is a protective holster that is there only for appearance, because it is very thin and will not provide any additional protection.

First annoyance: the sockets are all of the same color :  RED.
This can be easily solved with a black felt marker to make the common socket black, as it should be.
The second annoyance: the 2 volts scale is actually a (correctly labeled on the dial)  2000 mV, not the usual 2.000 V. There is no decimal point, and this results in confusion when reading (at least for me)
Third annoyance: to change the battery you must remove the holster and use a screwdriver to remove two self tapping screws, then open the case to reach the battery (a 9 V unit, supplied installed in the meter).
The battery is not insulated from the circuit, and a leaking battery may damage the meter.
Fourth annoyance: the rear tilt lid  is so short that the tilt angle is too small, making it unusable. The unit actually does not tilt (see photos).

The positive points are:
The very low price
The quality construction (that can be seen from the photos of the inside)
The small size and low weight
The well made rotary knob, easy to turn.
The meter is stable on the bench surface, and does not skip when rotating the knob.
The continuity buzzer is very fast (as Dave likes)
It is very lightweight, and it seem mechanically resistant: in fact tt survived two unintended  "fall to ground from the bench-top" tests.

For confidence, I've done a quick check of the correct meter operation in all function and ranges.
I did not test the accuracy, but it seems to conform to specifications (one or two digits of difference respect my 4 ½ digits "semi-calibrated"  Beckman).

PCB solder side:
a single 315 mA, fast blow, 5X20 mm glass fuse for  the 200 mA range (the PCB was designed with another fuse in the 10A range, but they soldered there a piece of wire). There is no trace of cutouts to increase creepage distances, but it's only 600 V rated…

PCB component side:
Input protection: I've traced a single protection component (a MOV or a PTC ?).
The meter IC is a mysterious COB component.
The rest of the circuitry : a dual op-amp, some diodes, some passives. a single trimmer for calibration.
The quality of soldering is good: no second-thoughts, no hand retouches.

I understand that this is not a professional meter: I have plenty of them, but I can use this for maybe 90% of my tasks. It is obvious that it is not suitable for high-voltage o high current applications, but next thief will have a really small gain….

Regards

[Kiriakos-GR]

I believe that this model is the Grandson of the UNI-T 30D 

[saturation]

A very good review ciccio, any low cost instrument can be purposed, so long as one is aware of it limitations.  Having a meter that can be stolen without worry does have it benefits.

I did the same, I kept a $10 DMM in my car for routine troubleshooting, and it lasted a 1-3 years, I forget.  What did happen, is exposed to the temperature extremes of my car, or poor workmanship, it simply died one day, and made me wonder about its reading accuracy far before it died; it certainly worked well new and I tested its accuracy, but as it aged, I increasingly became skeptical.   I also needed the meter right then, and now had none. 

I replaced it with an eBay $35 Fluke 85 and carry it a travel bag, which I always take with me when I leave the car, my first Fluke 85 is over 20 years old and has never failed or question the competence of its readings despite the exposed to very high ambient temps and humidity and the everyday jarring riding a car.

[Lightages]

I have a UT33C which is the same basic model but with temperature in place of the square wave output.

I too find it to be a well made meter especially for the price. It is a PTC as input protection, and that is all in addition to the fuses. I also like very much that the backlight is hard switched and does not time out! Yes, I hate the input jacks being all the same colour too.

I believe the case to be well made and with a very large overlap it should contain any blasts fairly well. But even so I would be very careful with its use around high energy circuits.

I tested mine against my two references here (DMM Check and Geller) and it is spot on at 5.00 volts and at 10.00 volts. The current measure (DC only!) read 1003 milliamps with a source of 1000 milliamps. The resistance reads 100.2kOhm on a 99.99kOhm resistor, 10.00k on a 9.999k, and 1.000k on a 999.7 resistor. I cannot say how accurate the temperature reading is.

I got mine for $8.000CLP here in Chile, or about $16USD. It is a good meter for automotive work and general low energy electronics. Yes, I have stuck the probes in the mains and I have still have my hands.

I would recommend one for a cheap second or third meter. Except for the lack of AC current measurement it does most things that are needed regularly.

[vk6hdx]

I just received a UT33A which is similar in appearance but auto ranging.

Quite happy with it so far, however the biggest concern with this series is that the volts and mA input is shared which makes it quite easy to inadvertently have the dial in the wrong place and blow the fuse.

Troy

[Chet T16]

I was thinking of picking up a couple of these, maybe an A and D just to have around

[Chet T16]

I was thinking of picking up a couple of these, maybe an A and D just to have around

Oh and in case anyone is wondering the differences between the versions (i was)

A - Auto Ranging
B - Battery Tester
C - Temp Probe
D - Square wave output

[vk6hdx]

Oh and in case anyone is wondering the differences between the versions (i was)

A - Auto Ranging
B - Battery Tester
C - Temp Probe
D - Square wave output

In true EEVblog style, I TOOK IT APART!

The UT33A seems to be pretty much the same as the UT33D on the insides judging by the photos above, although surprisingly it is powered by 2 x AAA cells instead of the 9V battery on the D model.  Also there is no backlight on this model.

I also found that one of the ball bearings under the range selector was not in place, I put it back in place and the switch feels much better than it did out of the box.

Troy

 

[ciccio]

It seems reasonably well made.
Is the autoranging function sufficiently fast or does it take a week for stabilization?
Regards

[vk6hdx]

It seems reasonably well made.
Is the autoranging function sufficiently fast or does it take a week for stabilization?

Hi Ciccio,

The Auto-ranging seems to work OK, it's not super fast but seems to measure a 100k resistance within about 1.5 seconds.

Troy

[Kiriakos-GR]

The most low cost DMM strangles mostly to measure low resistors like 3 to 50 Ohm.
Above the 100 Ohm mark they become somewhat faster.

In a fresh test of my, the UNIT-60 series, needed  3-4 seconds to measure 10 Ohms,
and the Mastech V&A 19 needed 7-8 seconds.
When the Agilent U1272A are instant = less than a second.



 
 

[vk6hdx]

Thanks Kiriakos, I'll try some lower resistance values and report back with the results.

[Kiriakos-GR]

Well just two words about my testing, I have build my own decade box ( https://www.eevblog.com/forum/index.php?topic=1148.0 ) and I feed lets say 10 Ohm, the DMM reads that, and then almost instantly I double the value.

Then the DMM jumps around so to detect the new value ... this is the time that I measure in seconds. 

I think so far that by this trick I have manage to exclude or minimize any delay added by the Auto-range function. 

[vk6hdx]

Nice, I like your decade box in the thread you linked.

My UT33a also takes around the 3-4 second mark to measure a 10 ohm resistance.

Troy
 

[qasarider]

Hi Ciccio,
Does the UT33D has any auto power off feature?

Thanks.

[Lightages]

I can answer that. No, the 33 series does not have auto power off.

[rubenmoniz]

I can answer that. No, the 33 series does not have auto power off.

http://www.uni-trend.com/manual2/UT33A%20Eng%20Manual.pdf
Page 27 claims that it does after 30 minutes

Hijacking the thread : I want to buy a multimeter like this one and it was suggested for it to be an auto-range one BUT whats the point in having auto-range if it takes 3 seconds to get a reading ?

[fsr]

I know that it is a very old thread, but i had an UT33C multimeter, and the rotary knob failed after what i'd call very light use.
At first i thought that i could fix it by re-tensioning the springs under the two metal balls that can be seen in the attached picture, but that really didn't do much, and the switch still fails intermittently, so the problem must be somewhere else. Maybe the vias, but the tracks don't look damaged in my unit.
It seems that you get what you pay for in this case.

Judging by the following video i found, it seems like UNI-T does still sell this model. They changed a lot of things in the board. The rotary switch plastic parts and spring-loaded ball bearings look the same. Almost all the plastic parts look the same, really.

[ledtester]

Appears to be the same as the Etekcity MSR-R500:

https://www.amazon.com/Etekcity-Multimeter-MSR-R500-Electronic-Multimeters/dp/B01N9QW620/ref=sr_1_fkmr0_1?ie=UTF8&qid=1546106063&sr=8-1-fkmr0&keywords=multimeter+budget

[badcon]

I have both old (about 10 years old) revision and new one (5 years old), just different models (UT33D and UT33C).
Plastic moulding is a little bit different, and have "NEW" stamped on it, I've attached pictures of both to see differences.
Old one uses latched push buttons for Hold/Backlight while new one is just rubber dome. Backlight doesn't timeout.
There is quite a bit differences on PCB, the new one have four trimpots while old one have just one.
Buzzer on old one is instant and not-latching type, on new model it have horrible delay of second-two and then latches.
Also, when overrange, new one will show "OL" while old one will show just "1". New one have white backlight which use single led.

Did anyone tried to calibrate these things? My old UT-33D is pretty inaccurate on DCV reading, I have schematics for it and I tried adjusting the only trimpot onto it. I can get volts right, but then after measuring on another range, it's still off by some amount. Newer UT-33C doesn't have that problems, it seems to be accurate, and it uses two trimpots for voltage reference (I didn't find schematics for new version). I've attached part of schematics from old version where is trimpot located, do anyone have any idea if i can mod it (with two trimpots, or whatever) to make it show reliable and accurate volt readings?