EEVblog 121GW Multimeter Issues

[EEVblog]

To which email address?

If i click email in the forum, i simply don't get an email address.

I also mailed to your eevblog.com contact address but no reaction yet.

I got it, just very busy right now.

[hainjedaf]

Ok. I'll wait. no hurry.
At least I know contact established.

[DavePrime]

AC volts function stopped working. When testing mains I initially got a good reading, then over the course of a few seconds voltage readings dropped to 0 and frequency reading would briefly flash 60hz then back to 0. A few hours later I testedmains again to document on video and voltage only read 75-80 volts, briefly made it to 100 and then dropped to 0 volts over a few seconds, same flashing behavior on frequency after this occurred. Now reading ~ 0 volts plugged into mains, the frequency reading will alternate between 0 and very briefly flashing 60. Any ideas? 

Video link

https://youtu.be/Xmz-QeD6Tpw?si=PQZffWXd8nblFL4A

https://youtube.com/shorts/xEucjcGsZ94?si=BhtVPb4WIAV2M0B4

[bicycleguy]

Don't recognize that + - symbol below Auto

[J-R]

I'm sure he's kicking himself as we speak...

[DavePrime]

Yes I did kick myself, and that did fix the issue. Changed the batteries a few weeks back and somehow one bad cell got mixed in and never noticed the warning was still on the screen.

[hainjedaf]

To which email address?

If i click email in the forum, i simply don't get an email address.

I also mailed to your eevblog.com contact address but no reaction yet.

I got it, just very busy right now.

I can understand the 'being busy' part.
Buut... We're a month in so... is there any progress?

Maybe something turned up in the two bins of multimeters just researched?
I'd be very happy with a broken 121GW PCB to unsolder good working input jacks from...

[EEVblog]

I can understand the 'being busy' part.
Buut... We're a month in so... is there any progress?

Sorry. It's in the shipping system now so I can't forget.

[KungFuJosh]

Is this model a Back to the Future reference?

[hainjedaf]

I can understand the 'being busy' part.
Buut... We're a month in so... is there any progress?

Sorry. It's in the shipping system now so I can't forget.

Thanks a milion. Hope my 121 GW will be a happy camper soon

Love that DMM, especially with ProbeMaster leads

[EEVblog]

Is this model a Back to the Future reference?

Of course.

[hainjedaf]

Hi Dave,

Austraila Post knocked on my door this morning.

Need to work tonight so tomorrow I'll rejuvenate the 121GW.

Thanks a Million. I'll post the result here

[aesteve]

Hi Dave. I recently got a broken jack in my 121GW . Found this thread through a search engine. Do you still send replacements? I've sent you an email.

[EEVblog]

Hi Dave. I recently got a broken jack in my 121GW . Found this thread through a search engine. Do you still send replacements? I've sent you an email.

Yep, send me an email.

[aesteve]

I already did. Maybe you missed it because I used a different mail account from what I used to register in this forum, or maybe I didn't send it to the right account. I'll send you it again from the other account. dave@eevblog.com eevblog.official@gmail.com <- is any of these correct?

[thm_w]

I already did. Maybe you missed it because I used a different mail account from what I used to register in this forum, or maybe I didn't send it to the right account. I'll send you it again from the other account. dave at eevblog.com eevblog.official at gmail.com <- is any of these correct?

The first one is correct. His instructions previously in this thread were to "put 121GW connector in the title".

[crispus]

Hi everyone,

I cleaned it, still doesn't work but the shim is not the issue as one could see the above pictures  but that lead me to the issue.

At close inspection it doesn't seem that any other component misses the magic smoke, ...
(Attachment Link)

After some fail attempts to source a new board (contacted the distributor (Welectron), they sent me to Brymen, Bryman sent me to eevblog and then was silence) I would like to give it one more try before send it to a better place.

But before going that rabbit hole, I have some questions:

• beside the schematic is there any other documentation to speed up the process?
• does any know if there are internal traces around the affected area?
• some higher resolution photos in the affected area (for a good one )?
• pcb parts placement would be great

Any tip will help.

Thank you.

[Kean]

Hi everyone,

I cleaned it, still doesn't work but the shim is not the issue as one could see the above pictures  but that lead me to the issue.

At close inspection it doesn't seem that any other component misses the magic smoke, ...
(Attachment Link)

After some fail attempts to source a new board (contacted the distributor (Welectron), they sent me to Brymen, Bryman sent me to eevblog and then was silence) I would like to give it one more try before send it to a better place.

But before going that rabbit hole, I have some questions:

• beside the schematic is there any other documentation to speed up the process?
• does any know if there are internal traces around the affected area?
• some higher resolution photos in the affected area (for a good one )?
• pcb parts placement would be great

Any tip will help.

Thank you.

That is significant damage, and I did something similar to my 121GW as shown back in post 1314 and in another thread at https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1599418/#msg1599418 (and earlier).

In my case I had mistaken measured a high voltage (1200V 25kHz from memory) that burnt my PCB, but after I cleaned the PCB to remove the burnt section it worked fine again.  For you to have a similar burnt PCB (although on a different section of the switch) indicates that your 121GW very likely was also exposed to a high voltage to cause the arc over and burnt FR4.

So, the first thing you need to is dig away at that burnt PCB surface a bit, and then wash it with some IPA.  The carbonised section is going to be conductive and is likely causing leakage currents between the pads of the rotary switch.

If that doesn't help (or even if it does), then you might want to check the state of the protection components close to the HY3131 chip, e.g. D13, Q1/Q2, and Q3/Q5.  If those seem OK (not leaky or shorted) then it is possible that your HY3131 chip is damaged.  The parts may not show visible damage, but still be causing your false readings.

[EEVblog]

After some fail attempts to source a new board (contacted the distributor (Welectron), they sent me to Brymen, Bryman sent me to eevblog and then was silence) I would like to give it one more try before send it to a better place.

But before going that rabbit hole, I have some questions:

• beside the schematic is there any other documentation to speed up the process?
• does any know if there are internal traces around the affected area?
• some higher resolution photos in the affected area (for a good one )?
• pcb parts placement would be great

Any tip will help.

Was this back in 2021 as per original post?
There is no other documentation I'm afraid.
As Kean said, it seems that would have to be dug out and potentially re-epoxied.

[Kean]

Any tip will help.

In that other thread I linked, there are some good tips to read starting at my original post and over the following week or so.
https://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1580530/#msg1580530

There was some helpful info reverse engineering the range switch contacts, but also Joe did some great video content showing what would be needed to cause such damage which then triggered my memory of the potential incident that lead to the damage.

Like you, after the PCB damage I was getting unexpected high readings (166V or OFL when measuring 12V DC).  This is a high impedance circuit, and unexpected leakage currents could cause the weird readings.  Cleaning up the burnt PCB sorted it all out.  Amazing nothing else was needed, and the protection components seemed to have done their job.

I hope this helps you sort yours out too.