Hi Dear, sorry for the late. It may be that the test leads are in poor contact, or the test leads are broken. Could you try changing the test leads and test again? And, is the measurement normal at AC voltage or AC/DC current range? Then we can better know what the specific problem is.

Yes, I changed the test leads (I have two pairs of other leads from the UT-210E and UT-30D), I also changed the batteries to new ones. I took two devices. I measure the voltage on a regular AA battery. Two devices ZOYI ZT-702 and UT-210E show 1.28V, and UTM-1139C shows 1.07V But the paradox is this. I took 5 AA batteries. 4 pieces of all devices show 1.55V, but one battery, as I wrote above, normal devices ZOYI ZT-702 and UT-210E show 1.28V, and UTM-1139C shows 1.07V. I took another AAA battery, two devices ZOYI ZT-702 and UT-210E show 1.6V, and UTM-1139C shows 1.34V. I set the laboratory power supply to exactly 10V. Two devices ZOYI ZT-702 and UT-210E show exactly 10V, and UTM-1139C shows 8.4V. And one more moment. When I turn the knob on the power supply, changing different voltages, sometimes the readings are the same, but mostly the difference is about -2V, and sometimes the difference is +/-0.2V both up and down.@@UniTrendTechnology​

@@UW5EPE Thank you for your details, and sorry for the inconvenience, you could contact the direct seller for calibration service.

I don’t know where to go for calibration or repairs in Ukraine. Can you give me some advice?@@UniTrendTechnology

​@@UW5EPE Hi Dear, you can contact your direct seller for calibration, the store where you buy it

Hi Dear, you can buy it on our official online stores: ➡www.aliexpress.com/store/3095007 ➡unitrend001.en.alibaba.com/ Also, Amason, shopee etc.

Hi Sir, yes. The English manual of UT139S is available in each standard individual packing.

If it is to measure the phase voltage, after determining which wire is the neutral wire, use the AC voltage range, connect the black test lead to the neutral wire, and connect the red test lead to the "phase wire" you want to test. By measuring one by one, you can determine which phase wires are; If you are measuring phase sequence, UT139 cannot measure phase sequence. Our UT262E, UT219P, UT195DS and so on to measure it.

Hi Mohammed, we have many other types of DMM that may meet your requirements. Welcome to visit our website to check.

Please i wanna buy UT136C+ where can i get it. Can you recommend and good store to buy it

​@@UniTrendTechnologyPlease i wanna buy UT136C+ where can i get it. Can you recommend and good store to buy it

​@@UniTrendTechnologyPlease what's your website

Hi Dear, thanks for reaching out. You could find your nearest UNI-T distributor/regional sales manager on our website's Where to Buy page - at bit.ly/3OsiDJO to contact for the purchase details.@@danielteyehuago1633