EEVblog 121GW Multimeter Issues

[Seppy]

I already posted in the discussion thread about a problem I have with Vac readings. Now I will switch to the correct place for this.

In 5Vac mode I get wrong readings.

Today I checked the ZERO OFFSET CALIBRATION and had to find out, that only in 5Vac range mode with shorted inputs I get a reading of 0,499xVac. With open input I get nearly the same value of about 0,5Vac.

In all other Vac (and Vdc) ranges I get 0,0xxV. So I tried to calibrate only the zero offset in Vac 5V range mode. During the count down it displays the 0,499xV and after the calibration I still have this offset with shorted inputs on the 5Vac range. At the end of the calibration countdown I see "OFF-E" for about half a second what is not mentioned in the manual.

I have two references from voltagestandard.com. The 121GW is spot on for all voltage measurements I can do (Vdc 0,350V up to 10.000V and Vac 5V).

So there must be something wrong with the 5Vac range mode of my 121GW.

Another thing happened today while testing for the first time. When I switched from left side off to V mode the meter did not turn on. I taped on the mode switch still in this mode and it turned on. So there must be another problem with my 121GW.

You can read my postings and realted answers if you want to get the complete story:
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1446232/#msg1446232
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447697/#msg1447697
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1447957/#msg1447957
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1465469/#msg1465469
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469130/#msg1469130
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1469890/#msg1469890

Thankyou for your message we are aware of your issue, the issue with the on-off is almost certainly due to the shim fix (this will be shipped to you at some point soon, it will resolve the issue if that is an issue). It does sound like your 5V AC range has an issue, there is a new firmware update coming out. It might improve the situation for you and if you did want to recalibrate it would be better to do it after the next update.

[Candid]

Thank you for the response. I will try to calibrate with the next firmware update. I really wonder what the problem is. In all other ac/dc ranges the zero offset is ok so it hopefully is something that can be fixed with a firmware update.

[Doctorandus_P]

Source code not available.
To me this was the biggest bug of them all and enough reason to not buy this meter.
I really would have liked to be able to add some customized measurements, without too much effort, but having to rewrite all firmware from scratch would cost me far too much time.

Maybe I'll revise my opinion when a "community" alternative version of the software for this meter becomes available.

[morrone]

Bug in firmware 1.10:  If you try to start logging to the SD card while there is no SD card in the slot, the meter locks up.  Granted, user error, but it would be nice if the meter displayed an error rather than locking up.

[EEVblog]

Source code not available.
To me this was the biggest bug of them all and enough reason to not buy this meter.

Name another commercial meter on the market that has open source firmware?

Maybe I'll revise my opinion when a "community" alternative version of the software for this meter becomes available.

We encourage that.

[Candid]

I already posted in the discussion thread about a problem I have with Vac readings. Now I will switch to the correct place for this.

In 5Vac mode I get wrong readings.

Today I checked the ZERO OFFSET CALIBRATION and had to find out, that only in 5Vac range mode with shorted inputs I get a reading of 0,499xVac. With open input I get nearly the same value of about 0,5Vac.

In all other Vac (and Vdc) ranges I get 0,0xxV[...]

Thankyou for your message we are aware of your issue, the issue with the on-off is almost certainly due to the shim fix (this will be shipped to you at some point soon, it will resolve the issue if that is an issue). It does sound like your 5V AC range has an issue, there is a new firmware update coming out. It might improve the situation for you and if you did want to recalibrate it would be better to do it after the next update.

Ok the new firmware is out. I flashed v1.15 and tried again. But it is still the same. In 5Vac range I have an offset of about 0,5V (shorted or opened port is nearly the same). I tried to calibrate the zero offset for the 5Vac range but it did not help. So there must be a problem with the 5Vac range of my 121GW.

What can I do? The shim fix did not arrive up to now bot I don't think it will help with this.

[Iagash]

Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

[Seppy]

Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

One important thing to know is that if you simply minimize the app it is still using the bluetooth device until it is properly closed this means if you opened another instance it will not connect as the bluetooth device is already in use.

[Scottjd]

Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

One important thing to know is that if you simply minimize the app it is still using the bluetooth device until it is properly closed this means if you opened another instance it will not connect as the bluetooth device is already in use.

Sounds  logical. As and admin do you have the power to modify the fist post in this thread?
I was thinking somehow of informing people when reporting issues to include as much details as posable. As with most trouble shooting issues or working on replicating the same issue the more details the better.
Like the OS or remote device being used to connect to the meter via Bluetooth. What app was used, and what version of the app used? And so on?
It’s usualy a time saver and others besides admins and EEVBlog employees can try to replicate the same issue and help confirm if it’s an issue that affects all or just one persons systems from an bad registered driver or older app version.
Just a thought?

[Iagash]

Firmware 1.15 has a regression vs. 1.10.

When connecting via bluetooth and disconnecting again by closing the app (or the bluetooth connection) no connection is possible until bluetooth is switched on and off on the meter.

That is unlikely as the Bluetooth is basically a UART-BLE bridge module and it hasn't been updated. It is more likely an update to windows or android that caused the issue, otherwise i'm not really sure how this could have happened.

I did some more tests and I guess it's the decreased data rate, that seems to cause a longer time to be able to reconnect. It just needs a lot longer until a reconnect is possible. I guess the BLE module resets the connection, when some buffer overflows when it couldn't send the data for some time making a new connection possible.

[Candid]

Didn't I already read about this? I am not sure so I post it here in the issues thread.

When I turn off the beeper and afterwards go to diode test I get a nonstop beep with firmware 1.15.

PS: On 19th april I got a message telling me that the repair parts for the 121GW have been sent to me. They still not arrived ;-(

[Seppy]

Didn't I already read about this? I am not sure so I post it here in the issues thread.

When I turn off the beeper and afterwards go to diode test I get a nonstop beep with firmware 1.15.

PS: On 19th april I got a message telling me that the repair parts for the 121GW have been sent to me. They still not arrived ;-(

That is another strange issue your meter has, do you have steps to reproduce? I've tried a few things and couldn't get it to hold on beep.

[knapik]

I believe that I used to have the same issue, and it was due to the wobbly knob not making correct contact with the pads.

[Candid]

Ok so I will go on waiting for the replacement parts and hopefully they will solve bot problems I have. I think I can remember that I already read about someone having this issue too here but could not find the post.

[Seppy]

@ Candid

Did you receive your shims and whatnot, any update with the issue you were having?

[Candid]

@ Candid

Did you receive your shims and whatnot, any update with the issue you were having?

No, I did not receive anything up to now. And no update to the issue except that it is getting worser. Very often from off to any position the meter stays off or resets/starts from time to time and still having the +0,5V with shorted leads on ac 5V-range.

I got the mail about the delivery on 19th May but without any tracking Url. Maybe you can track something but not me:
Your order is on its way!

We are pleased to confirm that your order has now been shipped.

    Our Reference: 11633

    Your Reference:

    Carrier: Plain Labels
    (Australia Post for within Australia)

    Carrier's Reference:

    Tracking Url:

[Candid]

Today I got the switch and shim and installed them. So now the known issue seemes to be fixed.

But the fault concerning my 0,5Vac offset with shorted input in the 5Vac range still exists. So there must be something else with my meter.
I have firmware 1.15 installed and I just tried ZERO offset calibration of the 5Vac mode and it is still at about 0,5Vac with shorted input. When I open the input it is slightly higher (about 0,499xV against 0,515xV). The other Vac ranges are ok this only applies to the 5Vac range.

[Scottjd]

Has anyone reported or noticed when you zero out the meter on voltage or resistance (I think all settings) and use the auto hold at the same time, the auto hold results ignore the zero out value when it displays the auto hold results.

Then if you turn off the Auto hold the relative triangle symbol is still displayed on the meter, but it’s not the truly zeroed out value being displayed. It’s the normal value ignoring the relative value it should be doing math with like you didn’t zero it at all. But the triangle is still displayed on the LCD. So I pushed the relative button again, instead of the triangle turning off it blinks on and off real fast and sets a new zero value.

Or, once you get the Auto hold reading without the relative value calculated into the Auto hold reading displayed, then turn off the relative set value by pressing the button again the triangle on the LCD does turn off and the Auto Hold is still displayed on the LCD. But it’s not doing any auto holding despite the LCD showing Auto hold being displayed, the meter will display the live readings with no holding at all or beep indicating it’s captured a hold.

Seems these two functions just don’t know how to work together or play nice with each other.

The other thing I noticed with Auto hold is it seems to have difficulties capturing changes in values when the meter is set in a manual range instead of auto ranging. I set the meter to a manual range, and probe the DUT like voltage from my power supply or voltage reference so I know it’s a steady contact source. No beep, not auto hold after maybe 5 to 8 seconds. So I remove the probes and try again, sometimes it will work the second time, sometimes it won’t. Then I try again if it doesn’t work and eventually it will beep and display the hold value captured. This issue seems intermittent. I tried it also changing the voltage when it didn’t work and still had the same intermittent issue, and I’m not talking about small changes in the value. I tested this with 2.5VDC differences or 5VDC differences in the voltage.

And then also Auto hold might capture a value and beep, but if you don’t immediately remove the probe from the point being measured really fast it will display a lower value as you disconnect the probes from the source.
Example, let’s say I’m measuring a 5V source. When it does a hold and then beeps, if I hesitate and wait a second before I remove the probe it will change from 5V to a lower value like 3.856V as I remove one of the probes. So I have to take a reading again and wait for the beep, and remove the probe from the points I’m messing really fast for it to keep and hold the 5V measurement on the display. The voltage source doesn’t change and stays powered on the whole time.

And it doesn’t detect small changes like mV or uV changes even when it’s set to the highest resolution using auto range or selecting a manual range. I think it’s looking for pre-set amount of change in the value it’s measuring before it will display a new hold value. I’m not sure how much difference it needs to see before it captures and display the new hold value? I think it’s between 35mV and 40mV?
I found myself reversing the probes between each reading before taking probing the next reading. This way I forced it to the negative value before taking the next reading so it would capture even the smallest change in the next reading in case the next reading didn’t have a big enough change in value that would result in dillaying the same reading as before. No new beep if the value change isn’t big enough, or you start to think it’s just not working on the next reading you take.

And I know this is common with some meter, so maybe I shouldn’t mention this next one. But like some other cheap meters the reading are more accurate if you don’t use auto hold compared to the auto hold results. This might be from the meter displaying the results to fast before the measument settles all the way or not taking a few samples before display the hold number?

As I type this I’m starting to realize the auto hold might be the main issue from the fist thing I wrote about using auto hold with a zero set relative value first. I think Auto hold needs a little code tuning in the firmware.

Latest firmware 1.15, just recveied it today.
Scott

[BiOzZ]

(i moved this here from the general discussion, was not aware this was a thread)
Got my multimeter today and it arrived with problems, the ohm mode is reading a constant 0 ohm, diode mode reads 1 volt, high Z mode gives an over range, wont read AC volts, 15v diode mode reads overload
anyone else having these same problems? any fix?

[BiOzZ]

Video of the issue is still being processed but the link is down below
https://youtu.be/sZZliqPRBJ4
my serial number is #420 (heh)

EDIT: i should add that AC and DC volt reading in the standard (non-lowZ) mode read fine (not sure about accuracy but it looks good enough compared to my UT61E)

[Mickatroid]

My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.

[BiOzZ]

I thought i would give a small update on my problem
The current ranges all work fine, the 1v in diode mode does appear at the output, the 0ohm on resistance does not, and it does output current that differs depending on range
inside all of the protection appears fine and intact with quick diode and resistor measurements
impedance reads what i would expect it to, but the 10mohm hybrid is sorta flapping around in the breeze, its still connected

im at a lost as to what it might be, but definitely appears to be a hardware fault, i have not looked under the switch or removed the PCB

[Scottjd]

Video of the issue is still being processed but the link is down below
my serial number is #420 (heh)

EDIT: i should add that AC and DC volt reading in the standard (non-lowZ) mode read fine (not sure about accuracy but it looks good enough compared to my UT61E)

It thinks your probes are closed. When you crossed continuity it sounded off.
I had some solder splash on one trace by the flux capacitor, at first it looked like the trace was broken or scratched. This is from the manual soldering of the jacks and fuse holders. You might have some solder splash causing this probe short?
Also check the 2 resistors by the 2 jacks that are used for probe detection,

It is a EEVBlog meter, encouraged to take apart and don’t turn it on. If you feel comfortable enough I would take a quick look, general visual inspection of the board to see if an solder splash is causing this. If so, might be an easy fix. It should just swipe off with a little pressure using a plastic tool. Theirs s lotmof flux left over on the manual soldered parts so of the solder splash short is under the flux you may need a little rubbing alcohol to clear the flux first. I wouldn’t bother cleaning all the flux, just the one you might see solder causing a short.

I also have a bodg hand soldered capacitor at the top of the open whole were the middle screw post comes through, C23. It also caused a resistor behind it to move off slightly.
I don’t know if this was changed or added after the board were processed. Or if this was just something they noticed that the cap was loose when they installed the shim? Either way if it is a change after then maybe to much solder their is causing a short. I can’t say it’s the best soldering job I’ve ever seen, actually it fairly bad. But I don’t want to re-do this since I don’t want it to affect the calibration.

And U17 had flux and burned flux around the chip, I think it was added later or reflowed manually.

Those would be the thee spots I would check first.
Scott
Just a thought.

[EEVblog]

My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.

Probably an assembly tolerance or some crud on the zebra strip. First report of that, thanks, will keep an eye on it.
The screen is protected by a strong polycarb window, so pressing on that does not, AFAIK, translate into pressure on the LCD itself.

[Scottjd]

Hi Dave, you did this video a while back with voltage. I’ve been trying to figure this out, and I think I finally figured out why my resistance testing is gettting such large differences in readings.

I haven’t had time to check the voltage and temperature change but it also didn’t jump out at me during basic testing so I’m assuming it’s probably ok.
What I have noticed is the resistor mensrment range being severely affected by the internal meter temperature. I’m going off what the internal temperature is showing on the meter.

Can you run this again in the resistance mode? Specifically the 50M resistance mode maybe with a 10M resistors? Although I’ve noticed the temperature affecting all resistance modes, the 50M ohm range seems to be the worse and most sensitive. The ambient temperature in the lab did not change more then 1C but the internal temp on the meter with backlight on went from 21.1C to 26.1C.

My Caddock 10M resistor at 0.1% tolerance is a 15ppm temp coefficient but as I mentioned the lab room temperature hardly changed at all. At internal meter reading temp it showed 10.005. By the time the meter internal temp reached 26.1C the resistor was reading 10.158. And the day my air con was off the lab was at 24.4C and the internal temp on the meter reached 28.9C and the reading was much higher at 10.356.

Despite the 10M resistor being 15ppm I also testing with Vishay that are 2ppm at 0.025% tolerances and those are affected also with all ranges I own 1, 10, 1K, 10k, 100k ohm resistors.
I will also note the 50M range seems to be the most sensitive jumping around a lot just going to push a button on the meter or waiving your hand around it.
I just want to know if this is mine only, or if you can repeate the test with the resistance mode and see if this is a common thing? And maybe the sensitivity can be adjusted in the firmware, it reminds me of your 2016 mV range video showing it being so sensitive that I believe was corrected with firmware or maybe a hardware change? If it not just mine maybe theirs a specific component this resistance mode uses that can be changed to something that has better temperature coefficiency?

The sweet spot for internal meter internal temperature seemed to be about 21.1C for all ranges.

https://youtu.be/Wwz_fdU17aQ