EEVblog 1520 - Troubleshooting a Faulty BM786 Multimeter

[EEVblog]

Looking at a faulty returned BM786 multimeter.
Warning: Some components were harmed in the making of this video.

[bob808]

That might be a possible short from manufacturing. Seems to be under the pins. 

edit: nah, looked again at other frames and seems like it is gunk that you scraped earlier.
also can the micro pull it's own rails high? shouldn't the on signal come from some other chip/circuit?
there was also another rail that was coming through an inductor, can't remember if you measured that. if the enable for the rail doesn't happen there might be other stuff that's not enabled.

[joeqsmith]

Best two shots I saw of it.  Maybe damaged during the testing or maybe fine and just looks like the back was blown off. 

Offer stands.  If you would like the Keysight for parts to repair yours I'll swap you.   

***
Someone had posted a link to a better view of U2.   Looks fine. 

[bob808]

Had another look at the video and I don't see you measuring the other rail (photo 1).
Also the line (photo 2) that should latch those +/-1.65V rails might very well be RESET which is low. Even if you manually enable those +/-1.65V rails all micros might be in reset. 
Those +/-1.65V rails seem like VACC for an ADC. So the other line might be the 3.3V digital for the chip. If that's missing, or RESET line is low, it might explain why you're getting nothing from the micro. 
So RESET might be low because of a bad voltage supervisor chip / part of its circuit.

[thm_w]

In the youtube comments, Dave verifies multiple hacked/missing/etc components on this meter.
Either production quality really slipped here, or someone did try to mess with it.

This would be one benefit of having a tamper sticker, not a "warranty void" one though.

[bob808]

I assumed it's a new unit because it had the plastic foil on the display.

[SiliconWizard]

If it got like this straight from production, this isn't pretty. I wouldn't expect something like this from Brymen.

[EEVblog]

Best two shots I saw of it.  Maybe damaged during the testing or maybe fine and just looks like the back was blown off. 
Offer stands.  If you would like the Keysight for parts to repair yours I'll swap you.   
***
Someone had posted a link to a better view of U2.   Looks fine.

Yep, I cleaned it up and it's fine.

[EEVblog]

If it got like this straight from production, this isn't pretty. I wouldn't expect something like this from Brymen.

Yeah, very poor hand soldering.
Most likely replacing missing components from the PnP.

[EEVblog]

I assumed it's a new unit because it had the plastic foil on the display.

About 9 months old.

[SiliconWizard]

I assumed it's a new unit because it had the plastic foil on the display.

About 9 months old.

Oh you mean that it had worked for 9 months before failing?

[EEVblog]

I assumed it's a new unit because it had the plastic foil on the display.

About 9 months old.

Oh you mean that it had worked for 9 months before failing?

Yes, just died one day. Was working fine and then it didn't.

[SiliconWizard]

Oh yeah. In this case, the bad touch-up in production may indeed have been the cause, and it wasn't caught during production tests - some soldering joint making intermittent short-circuit for instance, that ended up killing the microcontroller or something.

Some clients may ask to reject any non-functional boards after reflow and not accept rework altogether, but that would add significant production cost and would make the product much more expensive.
I don't even know if Brymen would accept that. And I guess your return rate is too low to be a concern (at least I hope so.)

[EEVblog]

And I guess your return rate is too low to be a concern (at least I hope so.)

Correct. No concern on my part.

[EEVblog]

LOL. EVERYONE including myself missed a major goof in this video. Can you spot it? It's not the fault, but it's something I was wrongly assuming. I can't believe not a single viewer picked me up on it! 

[armandine2]

in for a penny - was the battery pack correctly loaded ?

[Kleinstein]

Much of the test were to see if the µC runs and can be recognized from the debug / update interface.  If the µC is not running, chances are the LCD is not showing anything useful.

A suspect point could still be a power supply supervisor, if used. It may do more than enabling the supply to the µC, but it could also hold the µC in reset state.
The tricky point is that for the custom (could be just custom pin-out) µC it is not clear which pin actually is the reset input.
One may be more lucky with the LCD controller if this chip gets the same reset signal.

[floobydust]

LOL. EVERYONE including myself missed a major goof in this video. Can you spot it? It's not the fault, but it's something I was wrongly assuming. I can't believe not a single viewer picked me up on it! 

Beuller Beuller I just watched the video and think U1 is the DMM IC, it's got all the analogs heading into it. U16 I'd say is the MCU. But then the crystal needs to feed both. I'd beep out the TX, RX programmer headers to confirm where they go.
OT fake Ferrari just auctioned off. I thought it was REAL!

[EEVblog]

LOL. EVERYONE including myself missed a major goof in this video. Can you spot it? It's not the fault, but it's something I was wrongly assuming. I can't believe not a single viewer picked me up on it! 

Beuller Beuller I just watched the video and think U1 is the DMM IC, it's got all the analogs heading into it. U16 I'd say is the MCU. But then the crystal needs to feed both. I'd beep out the TX, RX programmer headers to confirm where they go.

  You are the only one who noticed!
Someone on the live show also got it after I mentioned it and urged everyone to guess at it.
https://youtube.com/watch?v=oJbX-xcq0XU&si=EnSIkaIECMiOmarE&t=6738

[bob808]

I was close, called the +/- 1.65V rails being for ADC.

[floobydust]

LOL. EVERYONE including myself missed a major goof in this video. Can you spot it? It's not the fault, but it's something I was wrongly assuming. I can't believe not a single viewer picked me up on it! 

Beuller Beuller I just watched the video and think U1 is the DMM IC, it's got all the analogs heading into it. U16 I'd say is the MCU. But then the crystal needs to feed both. I'd beep out the TX, RX programmer headers to confirm where they go.

  You are the only one who noticed!
Someone on the live show also got it after I mentioned it and urged everyone to guess at it.
https://youtube.com/watch?v=oJbX-xcq0XU&si=EnSIkaIECMiOmarE&t=6738

Hey that's pretty funny. I'm just used to having no schematic, drawing out the circuit blocks in my mind, when doing repairs. Having a schematic is a luxury.

I find the best engineers in electronics have no need to be an "expert" or be right all of the time. So what, something wasn't right, just move on.
But there's this social push for "experts", know it all's- who are of course crap as designers, repair techs etc. The art constantly humbles a person.

[EEVblog]

Hey that's pretty funny. I'm just used to having no schematic, drawing out the circuit blocks in my mind, when doing repairs. Having a schematic is a luxury.

I find the best engineers in electronics have no need to be an "expert" or be right all of the time. So what, something wasn't right, just move on.
But there's this social push for "experts", know it all's- who are of course crap as designers, repair techs etc. The art constantly humbles a person.

As I said in the video, most Youtubers would probably edit that out and forget it ever happened.
But I have no fear of being embarressed by a mistake made in the heat of filming.

[golden_labels]

Dave, you mentioned Brymen wouldn’t share schematics with you. I wonder: how much trouble would it cause to you, if someone from audience reverse-engineered the board and published the results?

[EEVblog]

Dave, you mentioned Brymen wouldn’t share schematics with you. I wonder: how much trouble would it cause to you, if someone from audience reverse-engineered the board and published the results?

Zero trouble, go for it.
I've even done a video doing some on the BM235:

[bob808]

So the micro was dead but also another IC? What could cause this? Overvoltage on 3.3V rail? Maybe the user tried hooking something up to the programming port and maybe used 5V instead of 3.3?
Will we get a part 3 where you go further?