Teardown of Unit UT139C - Page 1
Forum section: electronics / beginners

author: shovon134
author_rank: Newbie
timestamp: June 04, 2019, 03:16:58 pm
content: Uni-t UT139C Multi-meter teardown....UT139C is mid range, low cost, robust multimeter. It is manufactured by Uni-t. Uni-t is Chinesmanufacturer. They manufacture DMMs, Function generators, oscilloscopes etc. etc. Although the ut139cis from China but their accuracy, build quality is quite reasonable against the price. Some teardownphotos is bellow.Price:It is uni-t's mid range multimeter. Currently it's price is $52.99 in Amazone(https://www.amazon.com/Multimeter-Resistance-Capacitance-Temperature-Measurement/dp/B016JXASYE) and$48.99 in Banggood (https://www.banggood.com/UNI-T-UT139C-Electrical-Digital-LCD-True-RMS-Multimeters-Handheld-Multimetro-Tester-Ammeter-p-1020193.html?cur_warehouse=CN).Features:It is a 6000 count meter. It has a large display. Almost visible from both four side. It has backlight which can be turn off/on with button.Like all dmms it can measure both AC/DC Voltage & AC/DC current. It has dedicated position in therotary switch for millivolt, microampere, milliampere. Resistance, Continuity & diode test are alsopresent with Capacitance, tempareture & frequency. It also has a button for select range manually andhas buttons for Maximum/Minimum, relative(delta out), Hz/duty cycle. Has auto power off functionwhich can be disabled/enable. It has a unique feature called non contact voltage function(N.V.C). Itlites up a led no top off the display when it come to electric field. And also has the option to usea clamp to measure Currents upto 60amps. The clamp sold separately. The meter is true rms. I do notfound any true rms converter chip inside. It must be done in software. The meter runs on two AAbatteries. Has good battery life.Teardown:The meter has a rubber holster. Which make it robust. The meter is pretty sleek and compact with theholster. The battery compartment is separately attached with a metal threaded screw. I like theseparate battery compertment. Because I don't have to open the whole meter to replace the battery.the both input (mA/uA and Ampere) are fused. But only 600mA rated fuse is accessible when batterycompartment is removed. The whole case is attached using 2 self tapping screw on the bottom andclipped on upper side. Now I can peak in side the meter. The 600mA fuse is glass fuse. But 10amprated fuse is looks like HRC but I'm not sure. The meter has 4 MOVs, 2 PTCs and diode bridge forinput protection. Inputs are connected using screws. It looks rigid. It uses 3 high value resistor to make high voltage resistor ladder instead of one. It is a cheap method to make high radsistor ladded. The meter is a one chip solution. There are no potentiometer for calibration. But there is a eeprom. My gase is that the calibrationvalues are store in the eeprom. Which is good. The display module is screwed down with the PCB. Therotary switch is clipped with the circuit. The switch is soft. Rotary switch contacts are goldplatted. Hmmmm. No they are not. I'm just kidding. Because no one deserves gold platted multimeterwith that much price. They are not so good but not bad. Typical battery contact and buzzer. Soldiringlooks good.I published this post to get notice of dave. Because he never did a treardown or review video of this multimeter.