Uni-T UT70B DMM

This UT70B multimeter is made by Chinese manufacturer Uni-Trend Group Ltd (Uni-T).  Their products occupy positions in the low- to medium-cost part of the market, and enjoy a decent reputation amongst hobbyists.  Some Uni-T models are rebranded as Tenma and Voltcraft.

This unit arrives in a non-working state, but is simple to repair.

11 Responses to Uni-T UT70B DMM

  1. Harvey says:

    Not a bad looking multimeter and for general usage its ideal, nicely made pcb and adc i.c thats known to be reasonable 🙂

    I have thought about the UT61E a few times, but cant convince myself i need a new multimeter lol.

    Smashing writeup as allways 🙂

  2. M. Qasim Saharan says:

    Can I ask? How crazy its mV range acts?
    I have exactly the same meter. Its mV range seems very very much sesitive. For example, when I turn it on, it starts with an overload ‘OL’ beep. If I touch it or move while holding it in my hand or, say, bring it close to my computer it starts jumping around swiftly and not actually showing any proper reading. And when the probes are attached it becomes even more sensitive, almost crazy.
    Otherwise, the meter works fine.
    I must say, with no probes attached, it do starts settling down aftre some time. But with probes attached, it stays crazy.
    Can you comment on this behaviour, please.

    • modemhead says:

      I’m out-of-town right at the moment so I can’t check, but I do seem to recall that the mV range was very sensitive and “jumpy” which really is not too unusual for any multimeter, especially ones that have higher than the usual 10 Meg input impedance on the mV range. If you short the probes however, it should read zero or very close.

  3. Phil Anderson says:

    Great review. I lost one of the contact springs for the selector wheel. Do you know of a parts source for those? Almost new meter and now doesn’t work. Unable to find one for parts.
    Thanks

    • modemhead says:

      I have no idea where to find something like that for sale. I did fix a cheap-O meter recently that was missing a contact spring just like that. I cut a tiny rectangular piece from some thin brass sheet metal, bent it into a shallow “V”, then cut the slot with a thin cut-off wheel on a rotary tool. It does work, but I don’t know how low it will last, since the brass isn’t as “springy” as the original.

  4. Uwe says:

    Hello Mr. Modemhead,
    In my UT70B, 2 surface mount resistors have burned out, R31 and R32.
    I was wondering if you could tell me their values so I can replace them.
    Thank you for your help.

    • modemhead says:

      R31 & R32 are 9.00 ohm through-hole resistors on this unit. Soldered in parallel for a result of 4.50 ohms. The pair function as the mA range current shunt.

      • Uwe says:

        Thank you for your reply and help. I will first try to fix those 2 resistors. My problem is not the mA range but the DMM does not switch on anymore. So far I could only identify those 2 burned resistors.

  5. Alma says:

    My friend i hace this same unit sold as baw brand. Its showing overloaded OL issue. I should check for burnt resistors? Thanks from Argentina

  6. Goerge says:

    Many years ago I’ve bought a UT70B, a very good service DMM.
    Last month I gave it to a friend to repair the car’s alternator and he told me that the DMM was ok till he measured the 12V battery. After that, UT70B DMM worked no more…
    I suspect he measured the 12V on Continuity/Resistance/Diode/10 A range instead of Voltage,the reason that the DMM is defective now….
    I know that UT70B has good overload protection but is it possible to be damaged in that situation?
    …UT70B DMM shows nothing on LCD display when power on…also,no beeps…
    I also noticed that I can still activate the backlight and goes off after 10 sec…but,only when the rotary switch is on Diode,Capacitance,Frecvency,Temperature C/F, the activated light is dimmed at half of normal…no dimmed light for the rest of rotary switch positions.
    Related to this situation, please help me with some indications (measurement points, how to check if main IC ES51962Q still works and other directions) on how to repair and recover my UT70B, a very,very good DMM in my opinion. Also, how can I check if osc still works, same for display.
    Thank you very much in advance!

    • modemhead says:

      This DMM should not be damaged by 12V no matter what function it is set on. Even if the leads were plugged into the Amp or milli-amp jacks, the consequence should only be a blown fuse. Connecting it to the spark plug lead of a running engine would likely kill it however. Not sure why anyone would do that though.

      I found a schematic (PDF) in my archives. I don’t remember where I got it, so I don’t know how accurate it is. The design is relatively simple, because the Cyrustek DMM-on-a-chip does pretty much everything. Which doesn’t bode well if it’s not doing anything at all.

      All the important stuff is mostly inaccessible under the LCD assembly, so functional trouble-shooting is hard. There is a 4.0MHz 2Vpp sine on what looks like the crystal leads. If you can get a probe on any LCD line, you should find a slow (~60Hz) 3Vpp stair-step looking wave if the chip is actively driving the display.

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