If you have a UT55 and blow a fuse, be careful how you take it apart!
I had the bad luck that when I took the back off, the circuit board stuck to the front - and I stupidly took some screws out of the back of the circuit board thinking it was attached. It wasn't but the black range dial mechanism was - and it fell off when I finally pried the board off the front. Pieces all over the place. Two ball bearings and a rotor with 5 springy contacts. This photo shows it as it should be. Note the four screws & nuts showing around the black dial mechanism:
This next picture shows the contacts on the dial (upside down); each copper colored spring connects a circuit board contact in one ring to another in the adjacent circular pattern of contacts.
I think only one of these spring contacts fell out (bottom one on the outside) and I thought I put it back in the same place. But it doesn't work.
I have not dared try measuring a voltage, just the ohms range. It shows a big 1 with no connection and, briefly a number when shorted, then goes back to 1. I'm thinking that could only be because I have one of the contacts in the wrong place. There are 8 other places to put that one on the bottom.
Can anyone think of a way other than trial and error to fix it? It is a tricky little job to reassemble the black dial with two spring loaded ball bearings. I did write to UNI T in Hong Kong but no replay after 2 days.
I had the bad luck that when I took the back off, the circuit board stuck to the front - and I stupidly took some screws out of the back of the circuit board thinking it was attached. It wasn't but the black range dial mechanism was - and it fell off when I finally pried the board off the front. Pieces all over the place. Two ball bearings and a rotor with 5 springy contacts. This photo shows it as it should be. Note the four screws & nuts showing around the black dial mechanism:
This next picture shows the contacts on the dial (upside down); each copper colored spring connects a circuit board contact in one ring to another in the adjacent circular pattern of contacts.
I think only one of these spring contacts fell out (bottom one on the outside) and I thought I put it back in the same place. But it doesn't work.
I have not dared try measuring a voltage, just the ohms range. It shows a big 1 with no connection and, briefly a number when shorted, then goes back to 1. I'm thinking that could only be because I have one of the contacts in the wrong place. There are 8 other places to put that one on the bottom.
Can anyone think of a way other than trial and error to fix it? It is a tricky little job to reassemble the black dial with two spring loaded ball bearings. I did write to UNI T in Hong Kong but no replay after 2 days.
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!
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?
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?
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!
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.
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.
You're a better person than me. I would have have pitched it and got out one of my many free multimeters from Harbor Freight. 
