Author Topic: UNI-T UT61E with wrong dial seting  (Read 291 times)

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Offline rodrigopires

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UNI-T UT61E with wrong dial seting
« on: June 01, 2020, 01:54:24 pm »
Hello everyone! I have a uni-t UT61E and used it for quite a while now and last time i was going to mesure some resistors it showed capacitance mode and now it doesn't go normal... it doesn't even make a beep when changing from resistor to capacitor wich indicates it's in the same mode but i dont know what could be wrong. It didn't droped and everything functions as normal since last time i used it. Any explanation? Could it be the selector dial contacts?

Thanks!  :-+

Video: https://youtu.be/pr_os8ni2aA
 

Offline jxjbsd

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Re: UNI-T UT61E with wrong dial seting
« Reply #1 on: June 01, 2020, 02:09:31 pm »
Clean the PCB, or the spring
I have used it for many years, no problem
Analog instruments can tell us what they know, digital instruments can tell us what they guess.
 

Offline rodrigopires

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Re: UNI-T UT61E with wrong dial seting
« Reply #2 on: June 01, 2020, 02:50:12 pm »
opened it and clean it and still the same, there was no marks or debri on the contacts. To note that it happened suddenly last time i used it it was ok used resistance mode and today i found it like this...
 

Offline odium

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Re: UNI-T UT61E with wrong dial seting
« Reply #3 on: June 01, 2020, 02:59:41 pm »
hi,

could it be that you measured some cap without previously discharging it  ?

in capacitance mode, can you check if you have 1 khz signal at the probes ?

cheers

 

Offline rodrigopires

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Re: UNI-T UT61E with wrong dial seting
« Reply #4 on: June 01, 2020, 03:18:46 pm »
I don't belive so only used capacitance mode once or twice in years and with discharged capacitors (actualy was to measure homemade capacitor value). Tested capacitance mode with a 103 cap and it works ok 10nF in both modes resistance and capacitance  :-//
 

Offline PedroDaGr8

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Re: UNI-T UT61E with wrong dial seting
« Reply #5 on: June 01, 2020, 06:54:49 pm »
According to the logic table in the schematic, the only difference between resitance and capacitance is that FC4 is high (DGND) for resistance and forced low (V-) for capacitance. Since FC4 is normally high (DGND) via an internal pullup resistor, something is pulling it to V-.

This leaves two options:

1. Diode D4 is shorted to V- via FC1. If this is the case, removing this diode should force it into resistance mode (the capacitance selection would not work) as long as the internal pull-up resistor is undamaged.

2. The internal pull-up resistor is damaged. If after removing D4, the meter still insists on capacitance mode this is the most likely cause. A 2.5MOhm resistor between the FC4 pin (Pin 119) and DGND (Pins 3-5 or left leg of the voltage regulator) would mimic the internal pullup in the ES51922.

3. The internal circuitry for FC4 is damaged, the meter is toast.
The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." -George Carlin
 
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Offline rodrigopires

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Re: UNI-T UT61E with wrong dial seting
« Reply #6 on: June 02, 2020, 10:24:58 am »
Thank you PedroDaGr8 you went right to the problem! Did some mesurents and got everything right except for FC4 in resistance, capacitance and frequency mode. Also found a reprair series on youtube of the same meter with similar problem by DrCassette, in his case he changed D4 and added a 24 ohm resistor to ground. Next i will be removing D4 to se how it behaves.
 

Offline rodrigopires

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Re: UNI-T UT61E with wrong dial seting
« Reply #7 on: June 02, 2020, 11:47:36 am »
removed D4: left diode shorted and right diode ok.

Now i have resistance on resistance mode and mA on capacitance mode, everything else works ok. Diode replacement options? 1N400's or 1N4148? that's what i have in stock
 


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