Review and tear-down of the Ruideng UM34C USB Tester

In this video, I take the UM34C USB Tester apart as far as possible, go over its functions and verify its claimed accuracy specs for measuring voltage, current and capacity.

In summary (starts at 42 minutes into the video)

The UM34C does the basic job of measuring voltage and current on the USB bus really well as long as you don’t have to go below 4V and I definitely recommend it for that purpose. The results are accurate, the display is easy to read and if you have the Bluetooth version and the app, the spreadsheet recording capability can be very useful. Capacity and energy measurements work well as long as you don’t use the threshold. Don’t buy it for the cable impedance facility unless you have a suitable load.

I found instructions in English here: (updated link 30-Oct-2020)

My video on the electronic load is here:

[wakzy]

Wow! That is the way a product report should be done; detailed and clearly explained, recored both video and audio. Very well written script. Thank you.

[BuildingCenter]

First video by this guy that I’ve seen. Incredibly detailed, focused. Great documentation. Additional resources in the description box. Masterful presentation, overall. I benefit from YT allowing faster playback, and his excellent English. Thanks for smashing this teardown, TheHWCave.

[paulpearce]

So so much better than other reviews, which mostly seem to consist of "Look how many digits are displayed" and "look how many screens there are". Please keep making these detailed reviews that are a fix for my "want more in-depth tech. knowledge" habit.

[I]

A very well done review. It helped me to understand the cable resistance test feature, the manual for my UT25 wasn't clear enough. Basically a USB tester of this style shows volts and amps and the other features are mostly gimmickery.

[markusfister]

Very thoroughly tested! It's a pity you didn't check the functionality with a USB3 host and device. You might have been surprised!
I wanted to use it like that and connected it to a USB3 port an a computer and a load resistor. Only this type of load resistor had a USB3 connector. The current shown by the UM34C was far too low! BUT: If you connect to a USB2 load resistor instead, the measured current is correct. Connect the UM34C to a USB2 host, but using a USB3 load resistor, the current is correct, too!
Only if both, the host and the device, are USB3 the current measured is much too low! I disassembled the UM34C just like you did and took some measurements. And I discovered what I would call a design flaw. The UM34C has the current shunt resistor placed into the ground connection between the female USB3 connector and the three input connectors. On USB2 connectors there is only one ground pin, but on USB3 connectors, there is a second ground pin between the two superspeed data line pairs, called "ground drain". This signal (on pin 7) is usually connected to the same ground line as pin 4 in hosts and devices. But in the UM34C, pin 7 of the male USB connector is routed directly to pin 7 on the female USB3 connector on the other side and not connected to ground. This means, that as soon as you connect a USB3 host (which connects pin 7 and pin 4 to ground) to the UM34C and then plug in a USB3 device (which also connects pin 7 and pin 4 to ground), the UM34C cannot measure the current accurately, because there is effectively a second ground connection in parallel to the shunt resistor in the UM34C between host and device, and the curent flowing through this second connection cannot be measured!
IMHO the correct way of designing the UM34C would hava been to connect the ground drain pin on both USB3 type A connectors to pin 4 and not route it to the other connector independently, so there is only one ground connection between input and output (via the shunt resistor).
edit: spelling

[particlecloud]

Love the thoroughness and level of detail in this!

[keithking]

Wow!! I think that was the best review of a product of ever seen👏👏 you covered everything 🙏👌

[Sysshad]

Very good video, i like the technical bits!
Do note that if you are transmitting with the bluetooth transciever it will draw much more current then shwo in about 20:00

[lens]

Very comprehensive review and usable review. Thank you

[Petertronic]

Excellent testing and explanations, this is very useful. I think this tester is amazing for the price. I also have a BM235, nice meter :)

[davidforbes]

I noticed at 2:43 of your video, BTW an excellent video review/teardown, that the printed descriptions on the back cover do not match the various components on the PCB. Specifically, your cover shows an ON/OFF switch and a USB-C OUT designation that at 2:49 of your video, where you remove the back cover to reveal the PCB, it is apparent that there is no ON/OFF switch nor a USB-C OUT connector on your PCB. Just curious about this anomaly?

[richardfabish]

Nice review. I ended up buying one. One question - where did you find the document displayed in your video - the technical one about 6 minutes into the video?

[hallo_matthew]

Very detailed video! Thank you! Keep up doing videos!

[Vimes.]

I was a little concerned towards the end of the video when you noted the Android App version "phones home" - is that a real cause for concern...?

Also, unless I'm missing something really obvious here what actual advantage does this UM34C offer over the UM25C...?
I can imagine similar app concerns apply for the UM25C as for the other model..?
A shame that the app has to be downloaded from Mediafire and not within the Android app store.

Thanks for the informative review.

[downundergarage]

Best review on the web by far.. well done.

[wei]

Thank you for the effort in making this informative video.

[noakeswalker]

I now have the non-bluetooth version of this meter as a result of watching your review. It will get used for easily measuring currents that usb devices draw, and for measuring mAh into various non-usb diy rechargeable torches I've built over the years - need to make some adaptors for that you suggest here, I have turned off the 'record' threshold, well, I think it's actually 10mA because you can't dial in 0, but that's fine. It's a shame that only button display colours can be changed, but none of the actual measurement fields can - red on a dark background is quite hard to read sometimes ! Also, the exposed pcbs at the sides are a bit vulnerable as you said, so it will live in its storage box mostly...Otherwise, no complaints, it's very good. Thanks. Dave

[fvn]

Very useful and detailed video! Enjoyed every minute of it. Do you think the circuit can be modified to use an external power supply (a battery) to power the STM microcontroller so it can measure voltages below 4V?

[JesseGyger]

Excellent informational review. Keep it up!

[Noobinski]

Thank you for this still great ressource. I bow to the thoroughness of your expedition.
Since I want to test cables and comsunptions now and then I purchased such a device and am quite happy with it, based on your helpful insights.
Anyway the app now is available in app stores and I wondered if they - just maybe - fixed the problems you stated in the firmware, too.
The trickle charge data glitch remains, for the cable resistance measurement I will order an electronic load in the next days. Did that with seemingly stable loads until now, but I do not trust that much. Do you have a suggestion on what USB load generator to buy in 2021? Since your video about that is from 2018... Budget seems to be around 30 Euros regardless of which one you choose...