Brymen BM786 Power On Fault Investigation 

He sees that the owner soldered onto the boarder and instead of saying. Well you might have damaged it doing that, warranty void. He say’s no worries. And acts grateful that the owner took a crack at diagnosing it. A true gentleman. Even in business. Well done.

The second one is my multimeter. I'm glad/relieved you could replicate the issue. I was watching the video thinking "stop turning on, damn it! You're supposed to be faulty" haha.

I have owned several different brands of meters going back 30 years and currently use the EEVBlog BM786 Brymen. The meter is good and I have liked it, but if it ever breaks down "like new", I will never use that brand again because all the other meters still work.

i was thinking about buying one, changed my mind now. thanks for the video :)

So buy Brymen BM869s and never have any problems! At least for 2 years in the laboratory and at the workplaces, every day work I have not had any problems. There is even a case of working for 1 hour at - 5°C. My Brymen BM869s has 2.5 minutes of screen backlight support. Greetings from Bulgaria

Dave, regarding the first four digits of the serial number being the date code, are you certain the last two of the first four digits are the year? I have a BM786, and the first four digits of mine are 2132. Possibly a 2-digit year followed by a 2-digit week. Incidentally, I've had no issues with my BM786. I just love that meter!

Deja vu. Like a lost dream where only parts are remembered lol

Get Bryman to send chips back to silicon mfg for failure analysis

Don't turn it on, take... oh wait, never mind.

I have seen fault like this on other equipment where the problem was dirty push buttons. The CPU were trying to boot but by having a push button pressed when it was not expecting it (during boot) it would not work. After cleaning the push button contacts, it would work.

Just sold 3off old Fluke 85/87 and awaiting a 2nd Brymen 786. Must admit, I do like the Brymen DMMs.

Unfortunately I have the exact same problem with mine. Was there ever a fix?

Do you have the ability to re-flash the meter firmware, and see if that fixes it? I've been noticing many things with flash seem to die after a couple of years, like the flash gets corrupted. It would be interesting if a reflash would solve the issue.

Have experienced uC startup problems back in 1980s, as the crystal oscillator was flakey startup. Ultimately traced to uC manufacturer specified crystal was poorly matched to the uC oscillator on the chip. As a result occasionally the oscillator did not reliably start at power up. Correct crystal and matching capacitances are important to assure oscilator to begin. A marginal change to crystal Rs characteristic and the matching capacitors in oscillator circuit allowed more reliable oscillator startup. After changes only at very sub zero temperatures was the crystal oscillator able to rarely fail to start. Most likely source of oscillator startup is incorrectly selected capacitors on the crystal path, a mere change, only for example 15pF vs 22pF may change startup significantly. Very dependant on the chip oscillator design, and that can even be affected by chip batches originating from different chip manufacturing plant /site or chip redesign shrink over manufacturing life of a chip

I'm wondering if something in the programming is having trouble coping with rapid switching of functions - but only on meters with certain switches. (Break before make, or the exact order contacts switch, etc.) Just something about the mechanical tolerances bringing it out in certain units. I just wonder if swapping the switch's rotor from another unit will fix this.

Maybe MOSFET Vgs(th) variation combined with the circuit being just on the edge means some aging changes the Vgs(th) enough to not conduct? Or it might be a processor startup issue, or the crystal not starting up.

C67? vs C109. They don't exist but the poles C67 and C109 are interesting. As soon as the Q18 is unlocked, I'm curious about the status of the C65. Oscilloscope please. Why is resistor installed in C61. next to C3 and C2. It's as if the automatic parts selector, after looking around for a bit, replaced the C61 with a resistor without showing it to anyone. R78 in leg 1 of U20? If there is an R78, the regulator installed here is the adjustable one. Then where is the R76. 41:07 Where is the crystal (4.9152Mhz)? Do you think I installed the same software on thousands of devices and used the external oscillator, and then decided to use the internal oscillator on a few? What engineer does this? The polarity of the battery is marked on the back of the board, whereas the C54 was not marked on the side.

7:39 So you edited this and still left the part in where you say they're a year apart? They're a week apart, the first two digits indicate the year. It makes no sense to restart the serial numbering at 01 at the beginning of a new year.

So is it worth buying the BM786? I am currently choosing between the BM786 and the UNI-T UT71C. Which one should I choose?

1.202 mA. Reminded me of Apollo 11 - The 1202 program alarm was a warning from the Apollo Guidance Computer that its core processing system had been overloaded.

I've got an ancient Extech meter that has an eerily similar problem. Powers up in only certain switch positions, not always the same ones. Works fine once powered up. And now that I think about it, it seems to happen more often if it's been turned off for a few hours. Almost certainly not a switch or battery contact problem. Actually been living with this annoyance for a few years. Hm.

Could be something in FW boot sequence not following the ok/normal code path. E.g something not initialize correct and gets the FW stuck. I.e FW do not handle the situation correct, missing error handling.

Go, take it apart!

Dump it and buy a Kaiweet.

Maybe some bad batches? The BM786 is my daily driver, and I haven't had any issues.

Very weird. 1.2 mA... maybe the processor is starting, but the multimeter chip isn't? I wouldn't be surprised to learn the display initialization only happens after the multimeter chip is known to be running. Could be a good troubleshooting video, especially since you have a good one to compare against... 🙄😉

Intermittent short between mcu pins maybe?

Keep posting to twitter as watch on RU-vid as RU-vid notifications are very hit miss.

Through some deep thought and a few conversations with ChatGPT for its amazing insights, I think I've figured out the root cause of the fault... It's buggered!

So you killed it by powering it from 12V?

WTF didn't you try removing and replacing the batteries once you got it into the switched on but not working state???

no twitters dying, everybody's bailing on it and hates it now

And the root cause is....?????

0:50......Yeah, sure Dave....That'll be it....🤔🤔🤔 Don't patronise buyers like that....

I have many meters, but my Fluke 107 is my daily go-to meter. Just say'en.

Déjà vu

Dave is investing in stock, like Elon is convincing to buy Twitter stock, Dave also thinks he will be Richie rich.

Still, TL;DW. Dave being clueless.

F twitter.

F Twitter. Elon destroyed it

Crap

Wow - that now makes TWO boring and pointless videos from Dave on the same subject. Gee, are you paying us viewers for our time you wasted? 👎👎