Author Topic: EEVBlog 121GW Discussion thread  (Read 560741 times)

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Offline Scottjd

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Re: EEVBlog 121GW Discussion thread
« Reply #775 on: May 26, 2018, 11:34:02 pm »
Are the meters supposed to come with a pre-installed microSD card?
Yes. Sandisk edge 8gb in mine, but don't know if all the same.
So far they have all been 8GB sandisk cards from what others have said.
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Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #776 on: May 27, 2018, 02:07:09 am »
I found that when I took my meter apart the range selection knob had a smooth clicky feel to it, but when assembled with the shim it had a rough, grindy feel that I didn't like.

I observed that my meter had the same raised molding artifacts that Scottjd pointed out. So I did two things: I smoothed down the raised projections using fine sandpaper, and I applied a small amount of white lithium grease on the contact surface where the shim rubs against the meter back. Upon reassembly my range selection knob now has a smooth, silky and clicky action that it didn't have before.
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Offline Scottjd

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Re: EEVBlog 121GW Discussion thread
« Reply #777 on: May 27, 2018, 02:21:46 am »
I found that when I took my meter apart the range selection knob had a smooth clicky feel to it, but when assembled with the shim it had a rough, grindy feel that I didn't like.

I observed that my meter had the same raised molding artifacts that Scottjd pointed out. So I did two things: I smoothed down the raised projections using fine sandpaper, and I applied a small amount of white lithium grease on the contact surface where the shim rubs against the meter back. Upon reassembly my range selection knob now has a smooth, silky and clicky action that it didn't have before.
That’s great. I did the same thing. But I used a fine grit polishing dremel bit instead of sand paper. So far so good. I didn’t do any grease yet because I want to see if any dust is created or rubbing is still happening. I feared the grease would collect the dust from any other rubbing parts and it would make it hard to find the rubbing parts. And the grease may thicken if it had dust collected in it.  I’ll probably do anther tear down for a quick inspection in a month. But even without the grease it feel like most meters, if not better then some of the meters I own.
Keep us uodated on your meter and if you have any switch issues. So far mine is good, I don’t see removing those posts causing any issues. If you watch Dave’s switch testing video half of the circle posts wore down from the shim anyway and was probably the cause if the dust. And his shim had a small burr on it from the mounting wholes drilled in it, but my shim was smooth so I probably won’t see that.
I figure removing them just speed up the break in process without creating any dust.
Glad yours is working good now.
Scott
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Offline Candid

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Re: EEVBlog 121GW Discussion thread
« Reply #778 on: May 27, 2018, 11:47:56 am »
Yes, 4GB when I remember correctly.
 

Offline ANTALIFE

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Re: EEVBlog 121GW Discussion thread
« Reply #779 on: May 27, 2018, 01:00:21 pm »
For those with a 3D printer, I made a wall-mount holder which you can get here:
https://www.thingiverse.com/thing:2932921
 
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Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #780 on: May 27, 2018, 05:16:26 pm »
Can someone do a test on their 121GW to see if it's the same as mine?

1. Put the meter in resistance mode
2. Manually set the range to 0.000 Ω
3. Short the probes (use alligator clips so you don't have to hold them)
4. Expect to see a fluctuating reading in the 0.03 to 0.05 range depending on the probe resistance
5. Press the min/max button to capture the max reading
6. Now lightly touch the HOLD button with your finger and pull it away again (don't press it, just touch it gently)

What does the display capture?

On my meter the reading jumps up dramatically as high as 0.2, 0.3 or even 0.5 Ω

Something similar happens if I press the REL button to null out the probe resistance. Pressing the REL button makes the reading jump high, making it impossible to null out the probe resistance in this range.

Also, occasionally step 4 will show an anomalous reading, for example yesterday the meter showed about 3 ohms. It persistently showed 3 ohms even after turning the meter off and on again and after sweeping the dial through all the other ranges. The shorted probe resistance reading only went back to normal after I put the meter in DC volts and measured a battery. Then suddenly I got the expected 0.035 ohm probe resistance. I have not figured out what event causes the meter to get into this state.
I'm not an EE--what am I doing here?
 

Offline ChunkyPastaSauce

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Re: EEVBlog 121GW Discussion thread
« Reply #781 on: May 27, 2018, 05:51:23 pm »
Can someone do a test on their 121GW to see if it's the same as mine?

1. Put the meter in resistance mode
2. Manually set the range to 0.000 Ω
3. Short the probes (use alligator clips so you don't have to hold them)
4. Expect to see a fluctuating reading in the 0.03 to 0.05 range depending on the probe resistance
5. Press the min/max button to capture the max reading
6. Now lightly touch the HOLD button with your finger and pull it away again (don't press it, just touch it gently)

What does the display capture?

On my meter the reading jumps up dramatically as high as 0.2, 0.3 or even 0.5 Ω

Something similar happens if I press the REL button to null out the probe resistance. Pressing the REL button makes the reading jump high, making it impossible to null out the probe resistance in this range.

Yes I'm having this, meter goes way out of spec, 0.5 \$\Omega\$ or more, v1.17. It happens whether max mode is on or not. I also see it in dc mv range (especially 500mv) and the temp thermocouple mode. On mine range, hold, rel, and min/max buttons will do it.I pulled apart the meter to see if anything under the button membranes, but didnt see anything weird. Right now the REL and min/max functions often not usable in mv,ohm,temp modes. https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1561363/#msg1561363

Since you're checking hardware related things, could you check the 1kHz LPF? My unit seems to be way too low below 1kHz (starts to atten around 30hz). https://www.eevblog.com/forum/testgear/eevblog-121gw-multimeter-issues/msg1563436/#msg1563436

Also, occasionally step 4 will show an anomalous reading, for example yesterday the meter showed about 3 ohms. It persistently showed 3 ohms even after turning the meter off and on again and after sweeping the dial through all the other ranges. The shorted probe resistance reading only went back to normal after I put the meter in DC volts and measured a battery. Then suddenly I got the expected 0.035 ohm probe resistance. I have not figured out what event causes the meter to get into this state.
I don't think I've seen this one

 

Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #782 on: May 27, 2018, 06:06:22 pm »
Yes I'm having this, meter goes way out of spec, 0.5 Ω or more, v1.17. It happens whether max mode is on or not.

Yes, the display jumps regardless. Pressing the MIN/MAX button just makes it easier to capture the reading.
I'm not an EE--what am I doing here?
 

Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #783 on: May 27, 2018, 09:37:04 pm »
How to make the meter show weird readings:

1. Put the meter on the Low Z range
2. Measure the mains voltage (let's say 120.0 V AC)
3. Put the meter on the Resistance range
4. Short the probes

You may observe an anomalous reading of about 3 ohms, slowly declining towards zero.

On other ranges (like DC mV) you may observe anomalous readings too.

It's as if a capacitor is charged up and is taking time to discharge back to zero volts. (Or did something heat up and it's taking time to cool down?)
« Last Edit: May 27, 2018, 09:38:47 pm by IanB »
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Offline nidlaX

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Re: EEVBlog 121GW Discussion thread
« Reply #784 on: May 27, 2018, 09:42:25 pm »
6. Now lightly touch the HOLD button with your finger and pull it away again (don't press it, just touch it gently)
E field sensitivity perhaps? I've noticed the meter can be relatively sensitive near the LCD display. In fact, the display itself is very sensitive as evidenced by segments activating when pulling away the screen protector. That said, I don't think this meter is abnormally sensitive compared to other meters in its class.

In any case, can you check whether this is the source of the weird behavior?
 

Offline tautech

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Re: EEVBlog 121GW Discussion thread
« Reply #785 on: May 27, 2018, 09:46:17 pm »
How to make the meter show weird readings:

1. Put the meter on the Low Z range
2. Measure the mains voltage (let's say 120.0 V AC)
3. Put the meter on the Resistance range
4. Short the probes

You may observe an anomalous reading of about 3 ohms, slowly declining towards zero.

On other ranges (like DC mV) you may observe anomalous readings too.

It's as if a capacitor is charged up and is taking time to discharge back to zero volts. (Or did something heat up and it's taking time to cool down?)
Watch the vid Joe did recently where he's stressing MOV's and PTC's and I think you'll find answers there:
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1552690/#msg1552690
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Offline nidlaX

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Re: EEVBlog 121GW Discussion thread
« Reply #786 on: May 27, 2018, 09:55:18 pm »
6. Now lightly touch the HOLD button with your finger and pull it away again (don't press it, just touch it gently)

What does the display capture?

On my meter the reading jumps up dramatically as high as 0.2, 0.3 or even 0.5 Ω

Something similar happens if I press the REL button to null out the probe resistance. Pressing the REL button makes the reading jump high, making it impossible to null out the probe resistance in this range.
I just did a quick replication of this behavior for the resistance mode. I get no sensitivity on the Peak and Setup buttons, a little sensitivity on the Rel and Mem buttons, and high sensitivity on the Range, Hold, Mode, and Min/Max buttons around the magnitude you described.

The reading jumps are triggered by touching the buttons without depressing them and typically settle after 1 or 2 screen updates.
 

Offline ChunkyPastaSauce

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Re: EEVBlog 121GW Discussion thread
« Reply #787 on: May 27, 2018, 10:07:07 pm »
How to make the meter show weird readings:

1. Put the meter on the Low Z range
2. Measure the mains voltage (let's say 120.0 V AC)
3. Put the meter on the Resistance range
4. Short the probes

You may observe an anomalous reading of about 3 ohms, slowly declining towards zero.

On other ranges (like DC mV) you may observe anomalous readings too.

It's as if a capacitor is charged up and is taking time to discharge back to zero volts. (Or did something heat up and it's taking time to cool down?)
I just tried and does same on mine.
Stranger yet,
1 Take Low Z reading from 120Vac source
2 Switch to Hz and take reading from 120Vac source - watch the temperature plummet in the secondary display to well below freezing and then quickly recover to normal temp
3. After temp has recovered in secondary display, now check resistance with probes shorted - shows 0 ohms (somehow this corrects the ~3ohm offset) - edit, this doesn't correct the offset, zero ohm is shown when shorted, but non-zero resistances are still now incorrect.
« Last Edit: May 28, 2018, 05:34:22 pm by ChunkyPastaSauce »
 

Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #788 on: May 27, 2018, 10:11:14 pm »
a little sensitivity on the Rel and Mem buttons

The trouble is that when the meter is in the mΩ resolution range (0.000 Ω) the resistance you are trying to null out with the REL button is likely to be the same order of magnitude (20-40 mΩ) as the sensitivity of the button to the proximity of your finger, which renders the REL button ineffective. Also it doesn't even have to be a finger. I tested pressing the button with a plastic ball point pen and got much the same results.

Another factor that increases the problem is that the buttons only seem to react when released, not when pressed. Since it is the release action on the REL button that seems trigger the problem there is no way to "lock in" the action of the press before withdrawing your finger. (I can guess why this is though--the buttons are trying to tell the difference between a short press and a long press.)
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Offline Candid

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Re: EEVBlog 121GW Discussion thread
« Reply #789 on: May 28, 2018, 10:38:42 am »
Doing LowZ measurement on mains power you stress the PTC that warms up and so the readings need to settle until the PTC has cooled down to normal temperature again. Until this is done you will get wrong ohms readings.

As tautech already wrote watch Joe's video and you will unterstand why this and what happens.
 

Offline IanB

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Re: EEVBlog 121GW Discussion thread
« Reply #790 on: May 28, 2018, 05:05:31 pm »
Doing LowZ measurement on mains power you stress the PTC that warms up and so the readings need to settle until the PTC has cooled down to normal temperature again. Until this is done you will get wrong ohms readings.

As tautech already wrote watch Joe's video and you will unterstand why this and what happens.

That isn't the point. Explaining a wrong behavior doesn't make it less wrong.

It is quite reasonable that someone might be testing voltages on mains circuits and soon after might be testing wiring resistance/continuity (e.g. checking for a good ground connection) where a resistance in the order of half an ohm might be expected. So in this scenario the observed behavior of the meter would be wrong and misleading.
I'm not an EE--what am I doing here?
 

Offline ChunkyPastaSauce

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Re: EEVBlog 121GW Discussion thread
« Reply #791 on: May 28, 2018, 05:50:30 pm »
Doing LowZ measurement on mains power you stress the PTC that warms up and so the readings need to settle until the PTC has cooled down to normal temperature again. Until this is done you will get wrong ohms readings.

It's not just resistance, there's a large voltage offset in the dc millivolt range under short. 
 

Online Kean

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Re: EEVBlog 121GW Discussion thread
« Reply #792 on: June 01, 2018, 03:51:56 pm »
I've been travelling overseas, but now I am back in the lab earlier this week I finally upgraded my 121GW firmware and installed the shim on the selection knob.

Today I went to measure a 12V DC source and the meter displayed 166V.  :scared:  Then it decided to show OFL, even when measuring a 9V battery!

My initial thought was I had accidentally manually selected a low range, or it was in mV mode, or I stuffed up in alignment of the knob position during reassembly.  But the display matched the various selected range positions.  I took the meter apart and couldn't see any issue... until I removed the range selection switch... and the below image is what I found  :wtf:



I have not been measuring any mains or other high voltages on the meter.  The only thing that comes to mind is that the 12V I was measuring was at the input to a couple of POL DC/DC converters which was at the end of a long cable, and the DC/DC converters only had ceramic caps.  The DC/DC converter (my own design using TPS54622) is rated at 5.2V 6A out but was struggling to power a Raspberry Pi & pocket 3G router.  Measured with another (Tenma or EEVblog/Brymen) meter I was seeing only about 3.8V instead of the expected 5.2V.

I added a 330uF electrolytic capacitor at the input to each of two the DC/DC converters and it solved the problem, so I guess with the long cable from PSU to the ceramic caps was creating a nasty LC circuit and maybe causing some voltage spikes.  The cable was ~3m of 18AWG figure 8 speaker cable to simulate what was on-site, and it did help to clearly identify the equipment issue I was tracking down.

No (obvious) damage to the DC/DC converters, Raspberry Pi, or connected equipment, but apparently the meter didn't like it.  Or the meter came to me this way as I've hardly used it apart from measuring low voltages mostly out of my sig gen.  I doubt that as I'm sure I would have noticed this measurement issue in previous testing.

It was late when this happened and I haven't done further inspection or tried cleaning the PCB yet.

Any thoughts?
 

Offline Brumby

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Re: EEVBlog 121GW Discussion thread
« Reply #793 on: June 01, 2018, 11:51:23 pm »
Looks like something arced over on the Ohms range.  Nasty.
 

Offline Iwanushka

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Re: EEVBlog 121GW Discussion thread
« Reply #794 on: June 03, 2018, 07:11:45 pm »
Did everyone in EU got their shims/knobs? I still didn't receive them nor got an email that they were shipped
Backer #146 2xDMM
« Last Edit: June 03, 2018, 07:35:25 pm by Iwanushka »
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Offline Candid

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Re: EEVBlog 121GW Discussion thread
« Reply #795 on: June 03, 2018, 07:54:33 pm »
I got mine on 17th May in Germany. And I got an email 4 weeks before that it was sent to me.
 

Offline Iwanushka

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Re: EEVBlog 121GW Discussion thread
« Reply #796 on: June 03, 2018, 10:07:51 pm »
I got mine on 17th May in Germany. And I got an email 4 weeks before that it was sent to me.

Thanks, most likely mine slipped through all the spreadsheets, will ping Dave later.
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Offline Seppy

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Re: EEVBlog 121GW Discussion thread
« Reply #797 on: June 05, 2018, 07:55:09 am »
I've been travelling overseas, but now I am back in the lab earlier this week I finally upgraded my 121GW firmware and installed the shim on the selection knob.

Today I went to measure a 12V DC source and the meter displayed 166V.  :scared:  Then it decided to show OFL, even when measuring a 9V battery!

My initial thought was I had accidentally manually selected a low range, or it was in mV mode, or I stuffed up in alignment of the knob position during reassembly.  But the display matched the various selected range positions.  I took the meter apart and couldn't see any issue... until I removed the range selection switch... and the below image is what I found  :wtf:



I have not been measuring any mains or other high voltages on the meter.  The only thing that comes to mind is that the 12V I was measuring was at the input to a couple of POL DC/DC converters which was at the end of a long cable, and the DC/DC converters only had ceramic caps.  The DC/DC converter (my own design using TPS54622) is rated at 5.2V 6A out but was struggling to power a Raspberry Pi & pocket 3G router.  Measured with another (Tenma or EEVblog/Brymen) meter I was seeing only about 3.8V instead of the expected 5.2V.

I added a 330uF electrolytic capacitor at the input to each of two the DC/DC converters and it solved the problem, so I guess with the long cable from PSU to the ceramic caps was creating a nasty LC circuit and maybe causing some voltage spikes.  The cable was ~3m of 18AWG figure 8 speaker cable to simulate what was on-site, and it did help to clearly identify the equipment issue I was tracking down.

No (obvious) damage to the DC/DC converters, Raspberry Pi, or connected equipment, but apparently the meter didn't like it.  Or the meter came to me this way as I've hardly used it apart from measuring low voltages mostly out of my sig gen.  I doubt that as I'm sure I would have noticed this measurement issue in previous testing.

It was late when this happened and I haven't done further inspection or tried cleaning the PCB yet.

Any thoughts?

Do you remember what jacks were in use when measuring the DC/DC?
Were you using the meter for measurement of current, power or voltage?
 

Offline EEVblog

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Re: EEVBlog 121GW Discussion thread
« Reply #798 on: June 05, 2018, 08:16:18 am »
Any thoughts?

The energy to do that couldn't have come via the V jack, there is at least a PTC + 1K in series with every path. Even if the contacts shorted the VA range contacts and the ohms contacts, worst case path is V jack to GND via a PTC + 1K. So, it's weird  :-//
So I can only presume the path is via the low impedance A jack somehow...
Maybe one of the range switch contacts wasn't installed properly and was floating around? I presume you hadn't taken off the range switch before?, as that's required for the shim replacement.
 
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Offline EEVblog

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Re: EEVBlog 121GW Discussion thread
« Reply #799 on: June 05, 2018, 08:22:24 am »
Kean, can you post a photo of the range switch contacts please.
 


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