Author Topic: Ut61E ohm range problem  (Read 8896 times)

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Offline Cpx

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Ut61E ohm range problem
« on: June 12, 2013, 03:59:19 pm »
I discovered today that my ut61E started to act funny on the ohm range :--, jumping around and indicating wrong values,and settling very slowly..(in the minutes range).
It works somewhat ok for the higher ranges but i loved that i was able to measure lower values correctly.
Protection transistors are ok and i do not remember doing any mistakes except low voltage overload (<15 volts) on that range.
Any troubleshooting ideas are welcomed. :)

 

Offline mariush

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Re: Ut61E ohm range problem
« Reply #1 on: June 12, 2013, 04:53:00 pm »
Clean the probe tips with isopropyl alcohol.
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #2 on: June 12, 2013, 05:37:56 pm »
The problem is not in the probes..i tried with many pairs.
Also, a while after power on it indicates 0.00 ohm even with 0.33 ohm resistors.. |O
« Last Edit: June 12, 2013, 05:42:06 pm by Cpx »
 

JuanPC

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Re: Ut61E ohm range problem
« Reply #3 on: June 12, 2013, 06:17:33 pm »
are we talking about Uni-T_? http://www.uni-trend.com/ut61e.html
if yes,
have you checked the battery?
Duracell 9v battery lasts longer than other Alkalines, but has artifacts when reaching the end, others die too fast to notice.
...
if not that, i don't know about that model, i don't trust auto-range stuff.
i have the Uni-T UT70A + UT601, both complement each other Amazing,
http://www.uni-trend.com/ut70a.html
http://www.uni-trend.com/ut601.html

the only thing is that i had to change the fuses a couple of times in the UT70A, they blow if you measure volts "parallel" when still in amps "serial", strange artifacts appear when fuses are blown, strange capacitance of a well known part say 10uF & no hFE, are some symptoms.

Hope That Helps.
« Last Edit: June 12, 2013, 06:25:01 pm by JuanPC »
 

JuanPC

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Re: Ut61E ohm range problem
« Reply #4 on: June 12, 2013, 06:32:59 pm »
The problem is not in the probes..i tried with many pairs.
Also, a while after power on it indicates 0.00 ohm even with 0.33 ohm resistors.. |O

both my Uni-T, when measuring a short "0.ohms" still get 0.17ohms with the short probes, 0.33ohms with the long, using the UT601.
so a 0.33ohm resistor should measure 0.66ohm, no big deal, bigger resistors do not have that problem,
the UT601 has a capacitance adjust knob outside the unit to fine tune the UT601 when working in the <200pF~20nF range "No shorted probes needed, but probes change/affect the capacitance upto the 200nF range.", coincidence that the photo was taken at 200nF ? or just a lazy photographer that didn't have the time to tweak the 0 adj.knob.?


In the UT70A, with a short, the long probes measure -00.3ohm, and -00.6ohm with the small, in the lowest ohm range.
just internal calibration, problem is... no service manual to know what to tweak. :-//
« Last Edit: June 12, 2013, 07:16:50 pm by JuanPC »
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #5 on: June 12, 2013, 07:09:55 pm »
It worked fine for about 2 months light usage..
1 ohm resistor measures like this:(movie)
1ohm_error.avi
After about 5 minutes it reaches the corect value... :-//
So no calibration will fix this.. :-BROKE
« Last Edit: June 12, 2013, 07:11:35 pm by Cpx »
 

Offline PedroDaGr8

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Re: Ut61E ohm range problem
« Reply #6 on: June 12, 2013, 07:16:46 pm »
It worked fine for about 2 months light usage..
1 ohm resistor measures like this:(movie)
1ohm_error.avi
After about 5 minutes it reaches the corect value... :-//
So no calibration will fix this.. :-BROKE

What about higher resistances. The 200ohm range is on a separate line than the rest of the ohms ranges. That might help narrow down what is causing the problem.
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
 

Offline darrylp

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Re: Ut61E ohm range problem
« Reply #7 on: June 12, 2013, 07:30:21 pm »
After I did some mods to my ut61e, for changing the peak to min/max and to enable the auto power off feature. I at first didn't clean the flux properly. This gave me wrong readings on ohm and volts ranges..... I spent too much time looking at that common connector for a fault until going back to the soldering. Once cleaned its been fine ever since. Perhaps your meter is not particularly clean inside from the factory assembly ?

Sent from my HTC One X using Tapatalk 2

 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #8 on: June 12, 2013, 07:36:24 pm »
The 2.2kohm range fluctuates also but not as bad as the 220 ohm  and the  22kohm range even less but no range is fully stable.
darrylpm, i also did the backlight and autopower off mod but it worked fine after.
I resoldered the parts in the resistor section but it didn't help...

« Last Edit: June 12, 2013, 07:39:11 pm by Cpx »
 

Offline PedroDaGr8

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Re: Ut61E ohm range problem
« Reply #9 on: June 13, 2013, 01:43:44 am »
The 2.2kohm range fluctuates also but not as bad as the 220 ohm  and the  22kohm range even less but no range is fully stable.
darrylpm, i also did the backlight and autopower off mod but it worked fine after.
I resoldered the parts in the resistor section but it didn't help...

OK, here are the components involved in the OHMS measurement:
PTC1, Q1, Q5, Q6, Q8, R36 (200k Qty: 4), R6 (100), R33 (schematic says 100kF but I think it is 100k ohm), VR3 (10k, this said cap next to it), C7 (300pF) C13(10nF), C14(220nF), C15(330nF), C16(47nf). There may be more involved but thats all i can figure. I'd check each of these if you can. There are some other pins that may play a role as well but the ES51922 datasheet is quite cryptic.
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
 

Offline retiredcaps

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Re: Ut61E ohm range problem
« Reply #10 on: June 13, 2013, 05:12:33 am »
This may or may not help you?

I buy used, sometimes abused (unknowingly) multimeters.  I bought a "working" Fluke 77 III multimeter.

Initial tests showed everything was good.  A few months later, I noticed that the 320 ohms and 32M ohms range was out of calibration.  A 100 ohm resistor would never "settle" and it was reading around 98 ohms.  Same for the 32M ohm range.  A 10M ohm resistor was out of spec and the reading would never settle.

With generous help from ModemHead, I was able to find out that my PTC was bad.  A good PTC for the 77 III should read around 1K ohm.  Mine read 110K ohm.  I temporarily replaced it with a carbon film 1K ohm 5% resistor and now all ohms ranges are within spec and stable.

Now for the life of me, I can't find my resistor network that I used for the above tests. :palm:
« Last Edit: June 13, 2013, 05:15:15 am by retiredcaps »
 

Offline nukie

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Re: Ut61E ohm range problem
« Reply #11 on: June 13, 2013, 06:30:47 am »
Check the mode selector contacts for corrosion, the newer models come with just bare copper without gold plating. This is the ultimate performance in cost cutting.
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #12 on: June 13, 2013, 11:19:40 am »
I checked the contacts and all parts that PedroDaGr8 listed and are good. :)
Voltage at ovx pin (resistor measurement adc input) varies. Something causes a low frequency oscillation there and it has low impedance since 1 kohm resistor directly to Vin does not stop it completely. :-[
Reuploaded video:


« Last Edit: June 13, 2013, 12:15:14 pm by Cpx »
 

Offline jarvis

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Re: Ut61E ohm range problem
« Reply #13 on: June 13, 2013, 02:08:39 pm »
I checked the contacts and all parts that PedroDaGr8 listed and are good. :)
Voltage at ovx pin (resistor measurement adc input) varies. Something causes a low frequency oscillation there and it has low impedance since 1 kohm resistor directly to Vin does not stop it completely. :-[
Reuploaded video:


Do DCV/ACV/Cap/Diode modes work well ?
Could you measure some voltage of ES51922 pins ?   
V-(pin126) vs. GND(pin4) = ?   
V+(pin1) vs. GND (pin4) = ?
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #14 on: June 13, 2013, 04:15:07 pm »
AC,DC and CAP work ok.
V+:2.97
V-:-3.11
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #15 on: June 13, 2013, 07:48:30 pm »
Problem solved  :-DMM.It was dirt under and near the ic, but it was not visible..and only hot water washing got rid of it.
Still i was unable to fix a 350pf parasitic capacitance between OVX and IVSL.Please someone with this meter measure that capacitance if possible.
Also vr3 does nothing..i am unable to zero it with dead short on input. :(
Thanks a lot for your help :-+.
« Last Edit: June 13, 2013, 08:19:33 pm by Cpx »
 

Offline PedroDaGr8

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Re: Ut61E ohm range problem
« Reply #16 on: June 14, 2013, 04:37:45 pm »
So your meter is saying you have 350pF of capacitance with no leads plugged in? Mine reads around 50pF

Impressive on finding the dirt. I was going to say in general the ES51922 is a surprisingly rugged IC. Really, as I look at the other IC's that are out there for multimeters the Cyrustek IC's are some of the best all-in-one IC's there are. Intersil has maybe one but thats it.
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
 

Offline Cpx

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Re: Ut61E ohm range problem
« Reply #17 on: June 26, 2013, 03:16:15 pm »
So your meter is saying you have 350pF of capacitance with no leads plugged in? Mine reads around 50pF
No,the parasitic capacitance is between OVX and IVSL pins only, in capacitance range it measures 55pF.
Because of it i may have problems when measuring high frequency current.
 

alm

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Re: Ut61E ohm range problem
« Reply #18 on: June 26, 2013, 03:52:09 pm »
High frequency current? What is the bandwidth in current mode, and what is the impedance of this supposedly 350 pF of parasitic capacitance (not going to happen unless someone misplaced a cap) compared to the impedance of the shunt at that frequency?
« Last Edit: June 26, 2013, 04:48:57 pm by alm »
 

Offline PedroDaGr8

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Re: Ut61E ohm range problem
« Reply #19 on: June 26, 2013, 04:07:29 pm »
So your meter is saying you have 350pF of capacitance with no leads plugged in? Mine reads around 50pF
No,the parasitic capacitance is between OVX and IVSL pins only, in capacitance range it measures 55pF.
Because of it i may have problems when measuring high frequency current.

That sounds normal.
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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