Author Topic: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue  (Read 567 times)

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Offline daveyk

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121GW Voltage Readings WAY WAY Off.   Not a 121GW general issue. Moderator, if you think it is move this message please.

I was trying to trouble-shoot with my 121GW.  It hadn't used in several months.  I was checking out a few on-board power supplies of an instrument I am trying to check.  The 6 volt supply was reading 8.444.  I trouble-shot that for an hour then I used my Agilent DVM and it read 6.001 volts!  Son of a bxxch!!!

I've never used the 121GW for voltage measurements, just ohms and didn't like it very much for that and really just set it aside after that.  Now this.  I am using the exact same set of meter leads by the way, I just moved them between DVMs.

I think it may be time to give this 121GW a toss.  It never has been right since I bought it and now, I suspect it is over a year old now.

Dave
 

Offline NoisyBoy

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #1 on: April 28, 2020, 06:59:45 pm »
With reading this far off, the first thing I would check is to put in a fresh set of batteries.
 

Offline ggchab

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #2 on: April 28, 2020, 07:09:05 pm »
The position of the rotary switch is not always perfectly correct. I had the problem with the resistors'range a few times and it gave incorrect readings.
 

Offline rsjsouza

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #3 on: April 28, 2020, 07:09:13 pm »
Does teh voltage have AC components as well? If so, check:
https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg3015706/?topicseen#msg3015706

Otherwise, let me know if you plan to toss it... I may be interested. :-+
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline dcac

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #4 on: April 28, 2020, 07:26:57 pm »
Also check if the error persists if you change range.
 

Offline dcac

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #5 on: April 28, 2020, 07:30:27 pm »
oh and after having a very similar incident - for troubleshooting I now only use a DMM I know and can trust, and so far my 121gw doesn’t really qualify, though that being said when measuring DC voltages it’s been within spec. so far - at least as long as it’s been a clean DC voltage.
 

Online joeqsmith

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #6 on: April 29, 2020, 02:13:53 am »
121GW Voltage Readings WAY WAY Off.   Not a 121GW general issue
....
Dave

When I first started to test the two meters I bought, one made some bad measurements right out of the box.  I always assumed it was the switch as after a few cycles it cleared up.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline daveyk

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #7 on: April 29, 2020, 03:56:16 pm »
"Does teh voltage have AC components as well?"

I've tested it right on my E3632A power supply in parallel with my 34401A.

No idea what is going on.  It the batts are low, the indicator is not on.  It was fine about two months ago.  Now that I finally went to use it (instead of my Fluke handheld), it does this.
 

Offline daveyk

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #8 on: April 29, 2020, 04:05:23 pm »
"With reading this far off, the first thing I would check is to put in a fresh set of batteries."

Bingo!  It had four really nice Duracell AA batteries in it and did NOT get used much at all.  In fact, it has probably sat two months without being touched.

I wonder if this meter draw current went not turned on?

All I had was some really crappy Harbor Freight batteries to put in it.  I have to dawn the mask and head to Wallyworld today; I'll pick up some AA batts there, perhaps some Lithium AA.

Funny thing is, I did not notice a low battery indicator.  I really didn't notice anything wrong with the meter at all until I figured out it read worse than a dead dingo's willy-rod (or some weird term like that - lol).

Dave
 

Offline daveyk

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #9 on: April 29, 2020, 04:06:57 pm »
Thanks Joe.  It was bad batteries, although no low batt indicator for some reason.  I've seen portable instruments were the battery voltage was high enough to keep battery indicators from working, but could not supply current to properly operate the device.  That may have been the case here.
 

Offline daveyk

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #10 on: April 29, 2020, 04:15:43 pm »
It's working "Okay" again.  I guess that's close enough for trouble-shooting purposed.  It's how it always has compared to two certified 34401A metes.  I assume .003v low is good enough.  Now it the Auto-Ohm was just faster. v2.02 firmware.   It's acceptable now.

This thing just threw me for a loop yesterday and cost me about an hour and confused the heck out me. You have to rely on your test equipment.  As cool as this meter is, I most often grab very, very old Fluke 75 or very, very old Fluke 83 (just recently fixed the display). I trust those meters more than the 121GW.  I still waiting for when I need that 15v diode check, which would set this meter apart.

Dave
 

Offline NoisyBoy

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #11 on: April 29, 2020, 05:48:22 pm »
Good to hear it is back to normal.  I don't trust the low battery symbol on DMMs, and changing battery is an easy test, that's why I always suggest people to try that first before opening up the meter.

No matter how good a DMM is, I prefer to have more than one, ideally 3+.  That way, when one reading is off, I can tell which one is truly off. 
 
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Offline daveyk

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #12 on: April 29, 2020, 06:16:09 pm »
"Good to hear it is back to normal.  I don't trust the low battery symbol on DMMs"

There can be a science to battery level detection and it is not always the voltage (99% of the time it can be - lol), sometime rare times it can be a current delivery issue.

The 121GW us smaller and prettier than either of my mid-1980's Fluke 75 or Fluke 87.  Resistance AUTO mode still tests me at times.  It works well in manual range mode, but rolling through the manual mode selections still confuses me. I don't feel what mode/range you are in is well enumerated on the LCD.  I do not think it's a dot matrix LCD display, so we have what we have and enumeration can not be fixed in firmware.  Dave could have made better choices in the LCD display mode indicators during the design process.  It is what it is, I need to learn it better (although I shouldn't have to learn a DVM).

When you trying to repair an instrument, it is okay that the broken instrument confuses you, it's not okay for your test instrument to confuse you.

Again; thank you an take care.
 

Offline rsjsouza

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #13 on: April 29, 2020, 06:21:04 pm »
@daveyk, thanks for reporting back the outcome of your predicament. I haven't had issues with battery indicators yet, but recently I suspect that several of my banana probes are starting to bite the dust - that or the meters' jacks. When making a measurement, I have to frequently rotate the plugs or wiggle the cables to get a solid "near 0Ω" reading.

That drives me nuts when I make a reading and the measurement fluctuates...
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Online joeqsmith

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Re: 121GW Voltage Readings WAY WAY Off. Not a 121GW general issue
« Reply #14 on: April 29, 2020, 11:44:45 pm »
Thanks Joe.  It was bad batteries, although no low batt indicator for some reason.  I've seen portable instruments were the battery voltage was high enough to keep battery indicators from working, but could not supply current to properly operate the device.  That may have been the case here.

Odd.  I tried the production unit that was not stressed using a 10V reference.

Vbattery,  121GW Readout,  Low Battery Indicator
4.895, 9.999, Off
4.557, 9.999, Off
4.218, 9.999, On   (this is close to the threshold)
3.978, 9.999, On
3.768, 10.000, On (this is where the meter will start to go inaccurate)
3.301, 11.062, On
2.596, 15.723, On
1.963, 30.24, On  (this is pretty much where the meter will cut out)

How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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