EEVblog 1520 - Troubleshooting a Faulty BM786 Multimeter - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: December 20, 2022, 06:17:23 am
content: Looking at a faulty returned BM786 multimeter.Warning: Some components were harmed in the making of this video.

author: bob808
author_rank: Frequent Contributor
timestamp: December 21, 2022, 02:06:25 am
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2022, 05:34:41 am
content: 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.

author: bob808
author_rank: Frequent Contributor
timestamp: December 21, 2022, 11:53:57 am
content: 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.

author: thm_w
author_rank: Super Contributor
timestamp: December 21, 2022, 09:22:45 pm
content: 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.

author: bob808
author_rank: Frequent Contributor
timestamp: December 21, 2022, 09:44:57 pm
content: I assumed it's a new unit because it had the plastic foil on the display.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 21, 2022, 10:10:58 pm
content: If it got like this straight from production, this isn't pretty. I wouldn't expect something like this from Brymen.

author: EEVblog
author_rank: Unknown
timestamp: December 21, 2022, 11:12:34 pm
content: Quote from: joeqsmith on December 21, 2022, 05:34:41 amYep, I cleaned it up and it's fine.

author: EEVblog
author_rank: Unknown
timestamp: December 21, 2022, 11:13:21 pm
content: Quote from: SiliconWizard on December 21, 2022, 10:10:58 pmYeah, very poor hand soldering.Most likely replacing missing components from the PnP.

author: EEVblog
author_rank: Unknown
timestamp: December 21, 2022, 11:13:44 pm
content: Quote from: bob808 on December 21, 2022, 09:44:57 pmAbout 9 months old.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 21, 2022, 11:19:47 pm
content: Quote from: EEVblog on December 21, 2022, 11:13:44 pmOh you mean that it had worked for 9 months before failing?

author: EEVblog
author_rank: Unknown
timestamp: December 22, 2022, 04:08:49 am
content: Quote from: SiliconWizard on December 21, 2022, 11:19:47 pmYes, just died one day. Was working fine and then it didn't.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 22, 2022, 04:57:38 am
content: 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.)

author: EEVblog
author_rank: Unknown
timestamp: December 22, 2022, 05:21:33 am
content: Quote from: SiliconWizard on December 22, 2022, 04:57:38 amCorrect. No concern on my part.

author: EEVblog
author_rank: Unknown
timestamp: December 22, 2022, 06:43:33 am
content: 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!

author: armandine2
author_rank: Frequent Contributor
timestamp: December 22, 2022, 02:00:08 pm
content: in for a penny - was the battery pack correctly loaded ?

author: Kleinstein
author_rank: Super Contributor
timestamp: December 22, 2022, 04:23:55 pm
content: 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.

author: floobydust
author_rank: Super Contributor
timestamp: December 24, 2022, 03:01:05 am
content: Quote from: EEVblog on December 22, 2022, 06:43:33 amBeuller 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 justauctioned off.I thought it was REAL!

author: EEVblog
author_rank: Unknown
timestamp: December 26, 2022, 10:00:30 am
content: Quote from: floobydust on December 24, 2022, 03:01:05 amYou 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

author: bob808
author_rank: Frequent Contributor
timestamp: December 26, 2022, 12:16:14 pm
content: I was close, called the +/- 1.65V rails being for ADC.

author: floobydust
author_rank: Super Contributor
timestamp: December 26, 2022, 10:30:23 pm
content: Quote from: EEVblog on December 26, 2022, 10:00:30 amHey 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.

author: EEVblog
author_rank: Unknown
timestamp: December 26, 2022, 10:48:48 pm
content: Quote from: floobydust on December 26, 2022, 10:30:23 pmAs 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.

author: golden_labels
author_rank: Super Contributor
timestamp: December 27, 2022, 01:41:43 am
content: 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?

author: EEVblog
author_rank: Unknown
timestamp: December 27, 2022, 03:21:16 am
content: Quote from: golden_labels on December 27, 2022, 01:41:43 amZero trouble, go for it.I've even done a video doing some on the BM235:

author: bob808
author_rank: Frequent Contributor
timestamp: January 05, 2023, 04:59:07 pm
content: 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?

author: McBryce
author_rank: Super Contributor
timestamp: January 05, 2023, 05:33:24 pm
content: Hi Dave,this is a very off-topic question, but possibly an important one for many... Why do you have a large poster of a very questionable public figure displayed behind you? Or am I mistaking who that is? If that is who I think it is, I consider it very distasteful.McBryce.

author: thm_w
author_rank: Super Contributor
timestamp: January 05, 2023, 10:17:13 pm
content: Quote from: bob808 on January 05, 2023, 04:59:07 pmUnlikely user would have tried to program it.No other ICs were proven dead yet, youtube comments noted possibly low battery could cause that error.But the actual cause, who knows, could be ESD (dave didn't think so), or that rework job was wrong, or firmware corrupting to an unrecoverable state.Quote from: McBryce on January 05, 2023, 05:33:24 pmWhy not be more specific, that guy in a red and green christmas suit?Chances are most people don't care.

author: bob808
author_rank: Frequent Contributor
timestamp: January 05, 2023, 10:38:32 pm
content: If just that micro died than it can clearly be a random thing. Not worth pursuing further.

author: McBryce
author_rank: Super Contributor
timestamp: January 06, 2023, 10:11:55 am
content: Quote from: thm_w on January 05, 2023, 10:17:13 pmIt seems to be a picture of ex-Prince Andrew.McBryce.

author: EEVblog
author_rank: Unknown
timestamp: January 06, 2023, 11:17:31 pm
content: Quote from: McBryce on January 05, 2023, 05:33:24 pmI have no idea who he is, I found it in the dumpster and it's a joke with my live audience and twitter users who follow me when I found him in the dumpster.I presume it's some local businessman in my business. We call him Larry.Who do you think it is?https://twitter.com/eevblog/status/1526911165657681921

author: EEVblog
author_rank: Unknown
timestamp: January 06, 2023, 11:21:12 pm
content: Quote from: thm_w on January 05, 2023, 10:17:13 pmExtremely unlikely to be ESD in a previously working meter that was not taken apart. It simply just failed one day.

author: EEVblog
author_rank: Unknown
timestamp: January 06, 2023, 11:22:29 pm
content: Quote from: bob808 on January 05, 2023, 04:59:07 pmProbably not, unless I find something.Someone mentioned battery voltage, I'll double check that when I can, but I don't think it's it.

author: McBryce
author_rank: Super Contributor
timestamp: January 07, 2023, 10:12:10 am
content: Quote from: EEVblog on January 06, 2023, 11:17:31 pmMaybe it's just because the picture is so small (as you are in a sub-window), but it looks very like Prince Andrew from here.McBryce.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2023, 11:07:18 am
content: Quote from: McBryce on January 07, 2023, 10:12:10 amThousands of people have seen it, you are the first one to even suggest that.

author: McBryce
author_rank: Super Contributor
timestamp: January 07, 2023, 01:49:46 pm
content: Quote from: EEVblog on January 07, 2023, 11:07:18 amFace recognition was never my strong pointMaybe it's just because I recently watched a documentary about him?McBryce.

author: IanJ
author_rank: Unknown
timestamp: January 07, 2023, 04:38:06 pm
content: Quote from: EEVblog on January 06, 2023, 11:22:29 pm3.1Vdc is the power up cut-off on my BM786. Still powers up fine.Anything below that it doesn't power up at all (nothing on the LCD).Ian.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 07, 2023, 04:56:03 pm
content: Quote from: thm_w on January 05, 2023, 10:17:13 pmI wouldn't put it past a beginner to play with that programing connector and fuck up their meter in doing so.

author: Neutrion
author_rank: Frequent Contributor
timestamp: January 07, 2023, 06:11:34 pm
content: Is it possible to decap the chip properly to have a picture and see what went wrong? I am not aware of many troubleshooting videos about the inside world of a microcircuit. (OK have never looked for one) It would be interesting. We would finally also have a REAL teardown picture of our loved Brymen meters brain.In the design phase of chips it must be done, so people are possibly doing it. Maybe it would be a nice video as well. Once I saw a video about a german company producing the testers to test single transistors on the highest end processors.And if we are here, once I posted a question on this board what could cause the mass failures of Linkswitch LNK chips and the likes, but everyone was just guessing. However it causes huge amount of electric failures.I think there is no single other component in electronic history which alone caused so much trouble.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2023, 10:36:29 pm
content: Quote from: joeqsmith on January 07, 2023, 04:56:03 pmPossible, but from my communication with the owner it seems unlikely.And there is a history of BM235 chips just failing.

author: IanJ
author_rank: Unknown
timestamp: January 08, 2023, 01:20:27 pm
content: Quote from: EEVblog on January 07, 2023, 10:36:29 pmI've had two customer instances over the years where the Atmel uP just plain failed (PDVS2mini). Both times it powered down ok at last use, but the next day it just failed to power up completely (running on batteries only).I half think that maybe at power up or power down the 3.3Vdc regulator "fails" and maybe spikes through a higher voltage killing the uP.Ian.

author: Neutrion
author_rank: Frequent Contributor
timestamp: January 08, 2023, 08:55:45 pm
content: Quote from: EEVblog on January 07, 2023, 10:36:29 pmThe frontend, or the hy2613? Only a given batch is affected, or all of them? Is it known what is the process size used in these?Isn' it extreme rare that a chip fails without overvoltage? Sorry for the many questions!Because the frontend could get some spikes which get through, but the processor should be a bit more separated I suppose.

author: EEVblog
author_rank: Unknown
timestamp: January 08, 2023, 09:28:51 pm
content: Quote from: Neutrion on January 08, 2023, 08:55:45 pmThe processor. Doesn't seem to be batch related. It's not many but there is a history of it.

author: bob808
author_rank: Frequent Contributor
timestamp: January 08, 2023, 11:56:37 pm
content: I found this in its manual:Quote

author: EEVblog
author_rank: Unknown
timestamp: January 09, 2023, 03:37:29 am
content: Quote from: bob808 on January 08, 2023, 11:56:37 pmYep, but it doesn't go away when the amps range is selected, so it's something else at fault.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 09, 2023, 10:33:27 am
content: There is an report of the inEr occuring after water damage. So this could be thing with leakage or possibly a solder bridge / solder ball causing a short.

author: SeanB
author_rank: Super Contributor
timestamp: January 09, 2023, 10:42:29 am
content: IC failure is often from ESD damage at some early point, as it can take months to show up, even years, so it is insidious. Could be as simple as a broken ground lead on one of the PNP machines, but the ball races still provide a good enough path for discharge normally, only the odd chip gets zapped. Otherwise could be a die defect where a trace is just too small, and electromigration eventually makes it open.Water ingress and conductive paths causing Iner is also common, it can take a lot of washing to remove the contamination from the board and sockets.

author: Neutrion
author_rank: Frequent Contributor
timestamp: January 09, 2023, 06:23:16 pm
content: That's interesting, thanks! If you would happen to have any good links to this topic I could apperciate it.As far as I know also older (bigger) technology could be also more reliable if done properly.As for the ball races: I would supose, that in such enviroments already conductive grease is used.

author: bob808
author_rank: Frequent Contributor
timestamp: January 09, 2023, 07:23:32 pm
content: Could the "InEr" error come from a bad ADC chip?

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2023, 02:24:06 am
content: Quote from: Kleinstein on January 09, 2023, 10:33:27 amIn that case though the warning should stil go away when in the Amp range switch position.

author: Jeeper44
author_rank: Newbie
timestamp: March 25, 2023, 01:04:28 am
content: Around the 2:54 mark in the second video, 1522, you mention a content creator who has multi-series troubleshooting videos. Can you share that name again. I've tried searching based on what I think you said but haven't found them. This was right after mentioning Joe Smith.

author: Kean
author_rank: Unknown
timestamp: March 25, 2023, 07:42:23 am
content: Quote from: Jeeper44 on March 25, 2023, 01:04:28 amThat would be Defpomhttps://www.youtube.com/channel/UCllpBTH26_dAl5tYl7vA1TQ

author: NoMoreMagicSmoke
author_rank: Regular Contributor
timestamp: May 21, 2023, 05:21:08 am
content: Quote from: EEVblog on January 07, 2023, 10:36:29 pmIs this an issue specific to the BM235 chipset? Or is it a problem with the Hycontek processors in general? Have you seen many failures in the BM786 related to the processor?

author: EEVblog
author_rank: Unknown
timestamp: May 21, 2023, 06:15:16 am
content: Quote from: NoMoreMagicSmoke on May 21, 2023, 05:21:08 amThere have been odd failures were the chipset appears to be the culprit, but not confirmed by Brymen.

author: Phil_A
author_rank: Newbie
timestamp: November 18, 2023, 04:36:21 am
content: I just saw this video. I think the U1 "microcontroller" you are pointing to is actually the HY3131 DMM front end (48 pin). The NCs pins seem to line up. The pins you pointed to are AGND, REFO and VSSA on the front-end. The location of Xin/Xout seem correct and the HY3131 spec sheet specifies that 4.9152 Mhz Xtal. Perhaps U16 (64 pin) next to the buzzer is the microcontroller? Maybe U16 is a HY16F 32bit microcontroller? - Phil