EEVblog 1522 - BM786 Multimeter Repair PART 2

Part 2 of the BM786 troubleshooting repair, proving it's the processor at fault.
And Dave goofed up BIG TIME, did you spot the ERROR in the previous video?

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#ElectronicsCreators #Repair #Multimeter

[td]

I am glad that you followed through on the diagnoses.

[oida]

My BM869 shows that insertion error when the battery is really low. Might be the same issue here.

[iamdarkyoshi]

I work at an electronics manufacturer as the rework/repair tech, I've seen a lot of cases where it LOOKS like the MCU is dead, but there's another fault making the board fail, like a backwards chip on the same power rail as the micro that loads the line down when powered, broken resistors going to the programming header, lifted leads on the micro, ect

But given this unit has worked at one point and you were able to program a donor micro on the faulty board, it was definitely a dead micro in this case as you had suspected earlier.

The resistor change definitely is a bit odd though. Maybe a voltage divider that was changed to go hard to the voltage rail or ground? No idea.

[radarmusen]

I like that you don’t hide the goof, it happen to all being in a unknown territory.

[mikedjames]

Sometimes an STM32 will reconfigure its programming pins as GPIO either corrupted flash or intentional code options (program pins are alternate functions on GPIO) .. to recover you have to reset the chip and activate the pins in programming mode immediately before the application completes initialisation.. Which involved manually holding it reset then releasing with a normal programmer polling the SWD pins.. Then often needing a bulk erase from STs own utility rather than a third party programming application.. also the BOOT0 boot mode pin that invokes a boot loader is susceptible to noise and will crash the processor at any time if toggled over half the rate of peripheral clocks despite only being "used" just after reset to choose bootloader flash. We hit it with 10ns glitches by mistake and it crashed in one design.

[unclenemononame]

at 32:52 No not dumb or embarrassing. As a late in life beginner into electronics it is MOTIVATING! This teaches me that if even you can make mistakes. So can I and learn from them!

[JFirnQ]

That was awesome, I was invested wanting to know what the issue was. Was glad you had a donor board just to confirm it! Thanks for keeping all your goofs and process in the video, really nice to learn that way following your train of thought. I never fault you for goofs or anything, and I don't think others do... almost certain people prefer to see them like I do. There's a lot to learn in goofs!

Most definitely almost impossible to work at your normal capacity while thinking about the video you are making at the same time. Normally you'd just be silent completely absorbed in the debugging task, which absolutely would result in many fewer errors. Again, glad you leave that stuff in - rather than try to make your videos a showcase of your talent like others do. Anyone who holds that against someone's "skills/knowledge" simply hasn't ever tried making an engaging uncut video while working.

[TheDefpom]

You measured the processor voltage on the supply side or R150... I would be checking on the pins instead in case the resistor is open.

[kreature]

The "non working" chip may just be locked though.
If so, depending on how the protection works, it may need to be fully reset/erased or it may not be a reversible process when they blew the security fuses/locked it.
I also winder if the InEr is due to the fiddling with the xtal for the instrumentation chip.

[littletear]

If it so hard repair a electronic device for a guy that has " in theory" all information about that device, imagine how hard is repair for a guy that has no one information about that device.

[largepimping]

I appreciate the repair videos, and esp. the time you took to remove all the pauses/etc.

[DoctorMangler]

As a plumber I really enjoy your videos. I have a favorite plumbing flux too, other fluxes don't work the same. I've always wanted to fill some assholes electronics flux dispenser with plumbing flux. They'll love it at then in about a month the copper will be all gone from anywhere the flux was left on. The good part is there will be no traces to fix.

[SevenDeMagnus]

So cool, hands-on after learning amazing theories education on electronics from sir Dave.

God bless sir Dave.

[QsTechService]

Glad that you were able to solve the problem

[adagioleopard]

My boss once spend several houra debugging a memory leak in his code when the production team populated a 16K FRAM instead of a 64K FRAM.

It happens. :P

[dxdcbek]

Hey Dave thank you for the repair video. Now I wonder if swapping out the 000R resistor at R104 to 10K would resolve the problem sense that is the multi meter ic. And if that doesn't work then adding 150k resistor to R105.

[AngDavies]

Is the bus contention actually good? Implying some degree of logical progression/ life in the thing?

[MartinRepairs]

Notice difference between 17:08 (faulty unit) and 17:11 (donor unit)?






Faulty unit seems to have metallic hexagon screw type of head? shorting out something perhaps? or its just metallic color.
and donor unit has black plastic cap/head?

[KillerSpud]

I've lost many days of engineering time to stupid errors, the happen, don't fret it, accept three hard earned wisdom and nice on with your life.

[glottis]

can i ask you ... on silkscreen, the thick traces ... its for additional isolation or just info graphics?