Multimeter UNI-T UT55 problem

Thanks! What a pleasure to beat the "if it's broke, toss it" system.

Excellent job
Nice you got it fixed

Contratulations, you are now an electronics technician. :B Glad to see you found the diagram and the winning combination. :C :C

And the winning combination is:


I haven't received my 315 mA fuses yet, so I haven't tested measuring current. Ohms and Volts ranges work perfectly!

In my last email to UNI-T I included a link to this thread. Hey, UNI-T, sorry it is too late for you to share our joy at fixing the meter. If you have other customers asking for help you can't provide, you might send them here. We love to help people!

Interesting, Gene. Yes, I was looking at the same on on ebay.ca, where the prices range from $47 to $150. That is definitely where I would buy. I bought several of the UT204A clamp meters that way - great Christmas presents.

I am no longer doing guess and test. I found a schematic!!!
http://elektrotanya.com/multimeter_ut55_sch.pdf/download.html


The 200k middle ohms range has the line of contacts straight up on the circuit board (sorry I don't have that quite vertical in the photo).

I can't read the labels (R3, etc) but I can trace the connections to the ten concentric rings on the circuit board. I am pretty certain of the first and second rings as being the contacts connected to the resistors down the left side and the first column of heavy black lines. So there must be a spring contact connecting rings 1 and 2 (I'm calling that contact A) and it has to be on the very outside position on the rotor by direct measurement from the center point of the circuit board and the rotor. That confirms the location where I thought the wayward contact went. I'm pretty well convinced the 2nd and 3rd vertical black line patterns represent rings 5 and 6 just because of the line lengths matching the ring segments, and that they must also have a contact.

Also it strikes me pretty likely the far right line on the schematic and the contact points on its right side represents the two innermost rings - a third contact is already in that position I'm calling contact position K between rings 9 and 10. I have a feeling these make the display show in small print (200, 2, 200, 2, 20, 200) to indicate the ohms range selected, and similar for the other ranges. This feature works.

Two contacts to go, matching the double dark line segments down the middle of the schematic. This is a most interesting puzzle! Anybody have an insight into which rings those double lines represent and what they do?

Just for laughs I did a search for UNI-T UT55 and found one on Amazon. Price: $40.90 & FREE Shipping (don't know if it ships to Canada) Amazon meter link It looks almost exactly like my Cen-Tech P37772 from Harbor Freight. LINK

I have a UNI T clamp meter, too. I think both are excellent quality and well priced on eBay at around $50 Canadian including shipping from Hong Kong. The UT55 read 9.99 volts from my 10 volt standard.

I did tests with the contact in three different slots in an hour today. Slowing down now because I'll soon run out of possibilities. No reply from UNI T.

At first I thought it was a Hongkongemeter with Amps Jaws. There have been several threads on those here. Still this UT55 is way more meter than the free HF stuff and those Capacitance and Frequency features make it very useful for an RV'er wanting to work on Genset and Air Conditioner.
I guess your plan to get another one and make the parts match is a good one. I'm not sure I still have the coordination to work on those little parts but if you do, go for it. Are you sure you still have ALL those little contacts?

If I buy another one, the first thing I will do is open it up to see how to fix this one! Not bad - two good meters for $50!

Gene&Ginny wrote:
I don't know anything about that particular meter but here are a couple of ideas.

1) Look for wear marks on the circuit board to indicate where the springs may have traveled.

2) Most likely no 2 springs travel in the same circle on the circuit board. The picture seems to show 2 on the outer circle of the selector.

Thank you! The meter was a Christmas present so no wear on the contacts yet. Two will cut down on the trials.

If anyone has me of these meters and is thinking of having a look inside the black range selector, I suggest

- hold the circuit board upside down while you take out the four screws. The black range selector mechanism can't fall apart that way!

- hold the dial handle projecting downward as well as the big circular part (which is a cover for the dial itself) as you take the circuit board away. Put a couple pieces of tape on to hold the inside and outside together.
- take a picture in case something goes wrong and a clip contact pops off. Don't set it down - just hold it.
- reassembly: remove the tape and hold just as in the picture above but you need to get a finger or thumb above the board and a another on one of the nuts below while you put a screw in. You're safe after two screws are in.

Should the mechanism pop apart, it isn't all that hard to put it back together. Position the two ball bearings so they are touching the springs in the holes. Orient the rotor part so the two square holes allow you to see the ball bearings through them. Also turn so the ball bearings will be on an indent in the tooth pattern around the outside. I tilt slightly and push one side in place before the other but it may also work doing both sides at once. It actually pops into place without any fooling around adjusting the ball through the hole with a little screwdriver.

I guess you could measure dimensions on the circuit board between contact points and install contacts on the dial to hit them all. With a full-featured multimeter costing around $50, I wouldn't use a lot of my time on repairing that one.

FWIW, I bought fuses for my Fluke not too long ago. I slapped myself on the back until sore because I acquired the one $35 replacement fuse for a few bucks elsewhere. Within a week, I managed to blow it again, doh!