Why does my Uni-T multimeter not measure anything?

[antoniu200]

Hi! So, a couple of months ago, I got tired of me watching my movies and when someone flips a certain switch in the house, my Blu-Ray to stop working for a second, then come back on (the TV being fine, mind you, connected both at the same outlet). So, I took my multimeter (Uni-T UT33B) and tried to measure the voltage of my outlet when that switch is flipped. Dumb me, I set the multimeter for DC Voltage, while connecting the red cable to the Unfused connection. Of course, both the fuses in the multimeter and in my house blew.

Now, I replaced the fuse in the multimeter, but it still doesn't measure anything. I'll link a video in Google Photos of how it behaves when I don't have anything connected. I suppose there is a short-circuit inside the multimeter somewhere.

I'll also upload down below a photo of the board of the multimeter. If needed, I'll try and find a schematic of the board as well.

Any advice on getting this back up and running? I don't want to spend money on another UT33B, rather I'd buy a better multimeter, but I don't want to spend that kind of money right now, as I'll soon need a serious laptop for Video Editing and Android Studio, and those are very expensive.

The video: https://photos.app.goo.gl/uguwZCw7xSuwmTQu9

[petehall347]

Re: Why does my Uni-T multimeter not measure anything?

so you had it set up for amps then measured volts ? mmmm have done this to my meters in the past and gave up trying to fix and calibrate them .

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

so you had it set up for amps then measured volts ? mmmm have done this to my meters in the past and gave up trying to fix and calibrate them .

Well, I'd like to try my luck, as I might need that multimeter working soon. Here is a link to the schematic:

[stj]

Re: Why does my Uni-T multimeter not measure anything?

take the board out and check for burned tracks near the sockets

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

There are some burn marks at the joint of the socket with the board and with that big metal bridge, I'm not sure how to call it. You can see it in the pictures above. Can those marks cause the multimeter to malfunction?

[budm]

Re: Why does my Uni-T multimeter not measure anything?

It is hard to see. May be the trace is blown up.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

It is hard to see. May be the trace is blown up.

I thought about that. However, I'm not sure that can cause a short circuit in the multimeter.
I'll try and take a better photo of the burn tomorrow and upload it.

[budm]

Re: Why does my Uni-T multimeter not measure anything?

If the trace from the probe receptacle is blown then the probe is no longer connected to the meter circuit.
https://www.badcaps.net/forum/attach...1&d=1573479529
You have 3 probe socket, what are each one since we cannot tell which is which because there is pictures of the front side of the meter, also no pictures of the other side of the board that we can see.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

From down to up: Common, Fused, Unfused.

Bottom is Common, Top in Unfised.

[R_J]

Re: Why does my Uni-T multimeter not measure anything?

I thought about that. However, I'm not sure that can cause a short circuit in the multimeter.
I'll try and take a better photo of the burn tomorrow and upload it.

What makes you think there is a "short circuit" in the meter? Your video shows the meter working. When turned to 20MΩ it reads O.L that is normal, When turend to DCVoltage it reads 0.00 Volts which is correct without any "voltage" for it to measure. Have you tried it with the probes connected and placed in the Ω scale, short the probes and see what reading you get?

Like others have said, when you connected the meter in the "10 amp configuration" You would have likely vaporized the trace connecting the probe jacks to the circuit. That large wire bridge is the 10 amp current shunt for the meter You likely blew the trace connecting the common jack to the rest of the meter circuit

Was the black meter lead connected to the com jack when this happened? or was IT plugged into the VΩmA jack.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

The black lead was in the Common jack. The read lead was in the Ampere (Unfused) jack. I tried to measure DV Voltage with that configuration in an AC 230V outlet.

So, where should I resolder the Common jack? Should I take a wire and solder the Common jack to the large wire? Would that be enough?

What made me think there is a short circuit in the meter is the rise in resistance when I select Ω and then quick drop to OL. Same goes for voltage: see how when I come from resistance it rises and then slowly drops?

[R_J]

Re: Why does my Uni-T multimeter not measure anything?

NO. you should LOOK to see if there IS a blown trace. don't start adding jumper wires.
Have you tried placing the meter in Ω and check what resistance you get when you short the probes together? maybe the meter is working.
The way you had it connected, the large wire shunt was connected across the 10amp and COM jacks. That is what blew the house fuse. it was like connecting a wire across the house outlet. BANG

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

I did try that. It showed OL.

As for the blown trace, it's definitely seen some good black smoke. It could be blown, it could be fine. Not sure how to test that without another meter.

[R_J]

Re: Why does my Uni-T multimeter not measure anything?

If the trace blew it would likely be in this area. Is this where the black smoke is? clean any black soot from the board and provide a clear picture of this area. The COM jack likely connects to the end of shunt wire and also to a trace that connects the COM to the meter common circuit
If you look at the schematic you will see that the COM connects to one ind of R14 (0.01Ω) this is the large wire shunt. It also connects to the comon ends of R17,R29 & R30.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

Yes, that is exactly where the smoke is. I'll provide that photo tomorrow, as it's 00:29 right now where I live and at 06:20 I have to wake up.

[R_J]

Re: Why does my Uni-T multimeter not measure anything?

The blown trace could also be on the other side of the board, it is a double side circuit board.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

I'm pretty sure that trace is done-for.

As for the other side, it looks fine.

[R_J]

Re: Why does my Uni-T multimeter not measure anything?

Yes, that trace is gone, so get a thin piece of wire and solder it between the COM and the wire shunt. Using a thin piece of wire would be better in case the mistake is made again. I suspect the meter will work fine after that.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

Yes, that trace is gone, so get a thin piece of wire and solder it between the COM and the wire shunt. I suspect the meter will work fine after that.

Thanks! After I do that, I'll report back.

[antoniu200]

Re: Why does my Uni-T multimeter not measure anything?

As promised, I'm reporting back. The multimeter is back up and running.

Thanks to everyone who contributed!