Help Fixing UT61E MultiMeter continuously beeping

[pharaon]

wonder if some one can help me with the multimeter failure, the beeping on the dc voltage is not normal also the continuously beeping on the diode test is not normal.

i'v a video link showing the problem as well as schematic and photos for the multimeter board

https://youtu.be/NM1fsJOvq0o

[tunk]

Has it always been like this, or did it start recently?
Are the display readings correct?
Don't think it should make any difference, but you could try
to clean the contacts with e.g. IPA (buttons + PCB). Ditto for
the rotary switch.

[pharaon]

it never been like this, it start doing this when i accidentally shorted between the the 10A Max port and the + of the battery 

[JKKDev]

According to the schematic I would focus on the R36 and R6 resistors. I would try lifting each and see if the error persists.

I would also look at R20 and see what kind of signal gets there.

According to the schematic the buzzer is activated purely by the mcu so lifting the R20 should turn the buzzer off. It also means that something damaged either the detection circuit or the mcu itself.

The basic concept of diode mode is:
- +wire is a voltage source
- gnd wire is a voltage detection

By lifting the R36 you should lose the voltage source and by lifting R6 you should stop detecting voltage.

If the fault is external to the mcu the buzzer should stop sounding when you lift R6. If that's not the case the mcu got zapped.

If that is the case, there is a short between some voltage source and the path connected to R6 which is why the mcu is continuously detecting a short.

I hope any of this makes sense / isn't completely wrong :p

Just to verify I'm not talking total garbage I would measure voltages on the R36 (I'd expect around 3V or so), R6 (since the mcu hasn't gone up in smoke yet, but it keeps sounding the buzzer I'd expect around 3V as well) and the R20 (I'd also expect around 3V as it seems it's an enable for the buzzer driver chip).

If you're going to follow this please start with the R20 as that will tell us if the mcu is telling the buzzer to sound or there is a problem with the buzzer circuit itself.

(EDIT: after watching the video buzzer part seems fine. Concentrate on the R6. I wasn't able to find the R36 on your pcb image?? You can do what I descibed for R36 with the R33 and it should yield similar results.)

Sorry this is all over the place. It's hard switching browser pages on mobile

[mikerj]

it never been like this, it start doing this when i accidentally shorted between the the 10A Max port and the + of the battery

Did it blow the fuse?  Was the 10A range selected at the time this happened?

[pharaon]

 by lifting R6 you should stop detecting voltage.

If the fault is external to the mcu the buzzer should stop sounding when you lift R6. If that's not the case the mcu got zapped.

i removed R6 and still the same beeping problem, so i guess mean the mcu is already gone as you said
[edited] beside the buzzing thing it doesn't do any measurements

[goaty]

Simply remove the buzzer ...
Sorry had to write that. 

[goaty]

You short 10A and battery ? How does that go ? The battery of the Meter itself ?
If so, then you did check the 9V battery didn´t you ?

[JKKDev]

 by lifting R6 you should stop detecting voltage.

If the fault is external to the mcu the buzzer should stop sounding when you lift R6. If that's not the case the mcu got zapped.

i removed R6 and still the same beeping problem, so i guess mean the mcu is already gone as you said
[edited] beside the buzzing thing it doesn't do any measurements

Now that you've lifted the R6 you should be able to confirm that the pad opposite the mcu is connected to the ground output of the dmm when it is in the diode mode. This is just so we double check that what we are looking at is actually what we want

You could also try measuring the other pad of the R6 to see if there's a voltage present without anything attached (aka the mcu pin is internally shorted to some power rail).

If this turns out to be true I believe the mcu is dead.

EDIT: If that's the case you can get a new mcu for a third of the price of a new one of these. link

[pharaon]

Now that you've lifted the R6 you should be able to confirm that the pad opposite the mcu is connected to the ground output of the dmm when it is in the diode mode. This is just so we double check that what we are looking at is actually what we want

nope it's not connected to the ground it's connected to that part of the switch key


i also made some measurements between the blue circles marked spots and those were the values
R6 pin, vb- = 1.23 v
R6 pin, com = 0.94 v

[JKKDev]

You misunderstood me (I also didn't state it clearly enough). If you put the DMM back together (far enough that the rotary switch is operational) the R6 should be connected to the COM output of the DMM when the rotary switch is in the diode mode. If that's the case we know we are looking at the correct circuitry.

[pharaon]

If you put the DMM back together (far enough that the rotary switch is operational) the R6 should be connected to the COM output of the DMM when the rotary switch is in the diode mode. If that's the case we know we are looking at the correct circuitry.

yes it's the case

[pharaon]

Just to verify I'm not talking total garbage I would measure voltages on the R36 (I'd expect around 3V or so), R6 (since the mcu hasn't gone up in smoke yet, but it keeps sounding the buzzer I'd expect around 3V as well) and the R20 (I'd also expect around 3V as it seems it's an enable for the buzzer driver chip).

voltage on R6 the side of mcu is 3V

Now that you've lifted the R6 you should be able to confirm that the pad opposite the mcu is connected to the ground output of the dmm when it is in the diode mode

that is not the case it's not connected to ground output of the dmm when it is in the diode mode, actually it's connected to PTC1 and PTC1 is connected to V+ input terminal

does that mean the mcu is dead

[Ozan Bayram oglu]

Hi
I have the same multimeter. Why probes are displaced in Ohm mode?
COM = V+
V+ = COM