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Help Fixing UT61E MultiMeter continuously beeping

Harald Kapp

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No, the reference voltage is a fixed value.Expect 1.23 V.
 

pharaon

Oct 28, 2014
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ok it will be so difficult to do such measurement since it's on the U1 side of the board connected to R15 and to have any access to it i need to flip the board which won't allow me to have the key to turn the multi-meter on, and it have no check point to measure it on the back

PCB-Rear-New.jpg



i also notice something the D5, D6 i put in yellow rectangle are shorted but it's not the diode it's on the circuit, cause i took the diode out to measure and they were fine , is that normal?

 

Bluejets

Oct 5, 2014
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The meter indicates OL - overload. Does that happen when you short-ciruit the inputs (volt/ohm vs. common), too?

Check U1, pin #37, labeled VRH, for the presence of the correct reference voltage (1.23 V, see datasheet).


OL on the meter refers to Open Loop, not overload.
 

Harald Kapp

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to have any access to it i need to flip the board which won't allow me to have the key to turn the multi-meter on,
Solder two wi
D5, D6 i put in yellow rectangle are shorted but it's not the diode it's on the circuit,
You need to learn how to read a schematic diagram. There is a 9 Ω resistor in parallel to D5 and D6 which is what you measure as a short circuit. Measuring components while in
OL on the meter refers to Open Loop, not overload.
The manual I looked up states "overload".
 

Harald Kapp

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This is what comes from Chinglish translations.
I've (I think) never before seen a multimeter display "open loop". It would have to indicate "OL" any time no quantity to be measured is connected to the input. Meaningful in the resistance measurement position only. In the volts or amps range the display shows 0.000 (+. a few digits), not "OL".
 

pharaon

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You measure between the Vref pin of U1 and ground (0 V).
ok the Vref is pin 38 not 37 i checked on the pcb, and it have a check point on the back of the pcb
and those are the messurments
Vref , com1 = 1.38 V
Vref , vb- battery = 2.91 V


[Edited]
i also removed R6 which is connected to pin 20 "OVH" i think it's the detecting voltage, correct me if i'm wrong about that

so after i removed the R6 the beeping still exist which mean the mcu is gone, also correct me if i'm wrong
 
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Harald Kapp

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ok the Vref is pin 38 not 37 i checked on the pcb,
According to the datasheet, pge 3 Vref = Pin 37 - that is the output where a stable reference voltage of 1.23 V should be measured.
Pin 38 is an input and is the Vref divided by R15, R16 and VR1. The voltage on pin 38 should thus be less than Vref.
Your measurement of 1.38 V on pin 38 indicates that Vref is too high (or maybe oscillating, which you cannot identify well with a voltmeter).

A wrong reference voltage indicates a defect of the chip U1. A new chip is available for ~ 20 $. That's about 1/4 of a new multimeter. Might be worth a try if you feel your solderingskills are up to the task of replacing this chip.
 

Harald Kapp

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pin 37, com = 1.2
That looks good.
Honestly, I'm lost.
One more thing you could check: The input voltages at all the different measurement inputs of U1: pins 17 ... 29 (datasheet). Again measured vs. gnd/common.
Measure with the input terminals of the pcb shorted to avoid noise from open inputs.
These voltages should all be ~ 0 V.
 

pharaon

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i removed R6 which is detecting voltage, and the beeping still exist
i also measured the pad side of mcu after lifting R6 and it gave me 3v
is that normal? if it's detecting voltage according to the schematic

correct me if I'm wrong about it
 

Harald Kapp

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R6 is connected to pin 20 which is OVH. Acc. to the datasheet OVH is an output for resistance measurement. Seeing 3 V here doesn't seem to be unusual.
Sorry, I should have excluded that pin from the range of pins to be measured in my post #32.
What about the other pins I asked you to measure ? It intrigues me that from these pins you managed to pick just the one that is an output ;)
 

pharaon

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R6 is connected to pin 20 which is OVH. Acc. to the datasheet OVH is an output for resistance measurement. Seeing 3 V here doesn't seem to be unusual.
Sorry, I should have excluded that pin from the range of pins to be measured in my post #32.
What about the other pins I asked you to measure ? It intrigues me that from these pins you managed to pick just the one that is an output ;)

i'm working on it, just trying to exclude the pins that i don't need to wire it to be measured, also trying to find those pins on the mcu, on schematic is different than in real and the pins are really small
 

Harald Kapp

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also trying to find those pins on the mcu, on schematic is different than in real and the pins are really small
No, the schematic is a representation of the actual pin layout of the chip. But yes, the pins are small. You don't have to solder the wires to the chips's pins. find the component the pin is connected to and attach the wire there, if that is eaasier.
 

pharaon

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No, the schematic is a representation of the actual pin layout of the chip. But yes, the pins are small. You don't have to solder the wires to the chips's pins. find the component the pin is connected to and attach the wire there, if that is eaasier.

yes that's' what I'm trying to but what about pin 27,28,29 on the schematic they are not attached to anything
 
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