BM786 continuity beep not latched - Page 1
Forum section: electronics / beginners

author: woox2k
author_rank: Regular Contributor
timestamp: September 15, 2024, 09:24:07 am
content: Hello!I finally decided to stop buying random crappy meters and get annoyed by their multiple problems and purchased a BM786 meter. Everything seems to work but for some odd reason the continuity beep is not latched. First i thought that maybe i misremembered and this meter did not even have this feature but i have the same meter at work and its beep is nicely latched.Is this a fault of some sort or just a setting i can toggle on and off with some button combinations? I would not want to hassle with warranty since i ordered it from quite far away...

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 15, 2024, 11:09:05 am
content: What do you mean by latching? You want the beep to stay on even after the continuity is not there any more? If so I don't know of any meter that does that.

author: woox2k
author_rank: Regular Contributor
timestamp: September 15, 2024, 11:47:42 am
content: Quote from: BeBuLamar on September 15, 2024, 11:09:05 amNo, i mean that it behaves like the cheapest meters and doesn't have a well defined beep. With bad connection the beep sound is very scratchy.Random EEVblog video i found that shows this:https://youtu.be/ZoeUgMFLyAw?si=MJ41OxVKK8Re_QXn&t=1808At 30:08 that Elenco meter doesn't have a latched beep and this is the issue i'm having with my BM786.29:35 (Amprobe) is an example of a latched beep, this is similar how the BM786 should behave, just without the huge delay.It's not a huge dealbreaker but it worries me a bit since the exact same meter i have at work does not have this issue and the beep is nicely latched and quick.

author: Manul
author_rank: Super Contributor
timestamp: September 15, 2024, 11:48:58 am
content: I'm not familiar with the internals, but I'm guessing that on a modern multimeter latching must be controled in firmware? Or is it some hardware monostable type circuit? If it's firmware controlled, then I hardly see, how it can be broken. Maybe there is a latch duration setting and it's corrupted? Very strange indeed.

author: woox2k
author_rank: Regular Contributor
timestamp: September 15, 2024, 12:05:42 pm
content: Just for clarity i made a video showing this particular issue:https://drive.google.com/file/d/12fMtrt7vw-JQqA4WbSu3nWnJUhm-ETHO/view?usp=sharingI did use the cheapest chinese probes for this test on purpose because it makes this issue more prominent. With original gold plated probes the issue is not that bad because they have much better contact.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 15, 2024, 01:11:27 pm
content: Quote from: woox2k on September 15, 2024, 12:05:42 pmBuzzer not being latched is a good feature. It allows you to recognize bad (intermittent) connections by ear. Sure, the scratchy sound may be "annoying" to hear, but I prefer it because it has more information in it than a simple prolonged beep. What if you have a wiring harness with a broken wire that makes intermittent contact? Connecting my DMM to such a wire gives instant feedback about the connection while "massaging" the wiring harness to see If I can find the fault.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 15, 2024, 07:51:02 pm
content: Quote from: Doctorandus_P on September 15, 2024, 01:11:27 pmYes and the continuity beeper is only useful for intermittent problem. Otherwise I use the resistance measurement.

author: woox2k
author_rank: Regular Contributor
timestamp: September 16, 2024, 06:04:12 pm
content: Quote from: Doctorandus_P on September 15, 2024, 01:11:27 pmThat might be true but it did worry me because this meter shouldn't have this "feature"! Not going to return it under warranty because of that but i would be interested to know what causes that issue. Is it a firmware thing where they just changed some parameters between revisions or something in hardware?I don't even know how to check the firmware version on that meter. I kinda recall it being a thing but cannot find it in manual anymore...

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2024, 07:11:58 pm
content: Fast continuity beep is a feature people want. It's not an "issue", it's deliberate. Instead of a sluggish beep that is useless for finding a bad connection.Who needs a slow beep? Connection went open-circuit 200msec ago but still beeping?If you're not happy with it, send it back.

author: donlisms
author_rank: Frequent Contributor
timestamp: September 17, 2024, 12:26:55 am
content: It may also be good motivation to consider the cause(s) of the intermittent contact. Something to think about.

author: J-R
author_rank: Super Contributor
timestamp: September 17, 2024, 04:18:03 am
content: Quote from: woox2k on September 16, 2024, 06:04:12 pmCan't agree with any of the replies. The continuity beeper on the BM78x is supposed to be latched.Proof:https://youtu.be/WuNLEQfudnw?t=990https://youtu.be/Vd2PGLwPdhQ?t=669https://youtu.be/YHuy2PYNq68?t=1458However, it's possible Brymen made a change to the firmware without disclosing it, although I really doubt it. You can view the firmware by holding the Delta (relative) key during power-on.So I suspect your unit is faulty. When/where did you purchase it?I also tested my BM789 FW version 05 (BM786 adjacent) and under no circumstances could I get it to be scratchy despite fully exploring the ~295 Ohm trigger point. It either beeps or it doesn't.

author: woox2k
author_rank: Regular Contributor
timestamp: September 17, 2024, 01:32:09 pm
content: FW version shows up as 78611 (version 11 then?)Next time i'm at work i'll check the meter FW version there too.Nevermind, called them up and asked. It's 78607.So there is significant difference between versions. Highly doubtful but maybe Brymen did mess up the beep timings with new version (mishaps like that do happen sometimes). Then again, maybe latching is done in hardware and i just happen to have some bad capacitor or something on the circuit board...Both these meters are purchased from Welectron (Germany) Mine is few months old and one at work is couple of years old.

author: floobydust
author_rank: Super Contributor
timestamp: September 17, 2024, 07:53:38 pm
content: The word "latches" is incorrect. It really is a (continuity) triggered one-shot (in firmware) that extends the beep, a pulse stretcher.It looks like changes have been made to the F/W in the BM789 similar to what you are seeing:https://www.eevblog.com/forum/testgear/bm789-continuity-behaviour/25

author: J-R
author_rank: Super Contributor
timestamp: September 17, 2024, 09:36:14 pm
content: The latching term is somewhat common. It's even mentioned in one of the videos I linked.The issue in the other thread isn't the scratching.I would loop Dave in on this issue and get clarification on whether it's a conscious design change or an issue with that DMM that requires a warranty replacement.

author: woox2k
author_rank: Regular Contributor
timestamp: September 18, 2024, 05:58:28 am
content: Quote from: J-R on September 17, 2024, 09:36:14 pmSome explanation from Brymen would be perfect. I don't think i would hassle with sending it back to Germany either way but the whole point of this thread was to get some explanation to this, bit annoying but not dealbreaking, issue.I should have bought 121GW instead! Silly me believing that getting a meter i had already used and liked would be best idea. Just my luck i guess...

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 06:45:41 am
content: Quote from: woox2k on September 15, 2024, 09:24:07 amI'mNo one has ever complained that the BM786 does not have a "latched" buzzer.It literally gives you one solid loud tone, and none of that "scatchy" noise, which is the definition of "latched" vs "unlatched".Are you sure you not confusing it with the diode beep mode? (whcih is also "latched" but has a big delay)

author: woox2k
author_rank: Regular Contributor
timestamp: September 18, 2024, 06:49:06 am
content: Quote from: EEVblog on September 18, 2024, 06:45:41 amThanks for taking your time checking this thread out!Few posts down i posted a link to a video showing the issue i'm having. This is recorded by me showing this particular meter:https://drive.google.com/file/d/12fMtrt7vw-JQqA4WbSu3nWnJUhm-ETHO/view?usp=sharingIt is in continuity mode and it really does not latch. The sound is scratchy with intermittent contact!

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 06:52:53 am
content: Quote from: woox2k on September 17, 2024, 01:32:09 pmWoah, I just took out a new stock 786 with 78611 firmware and sure enough it's a way faster latch than 78607 I normally use in the lab.Have to go to the gym now, will shoot a comparison video when I get back.I can make it be a bit "scratchy" with very lightly toughing probes, but it's still obviously "latched", it's just faster at the release time.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 06:54:13 am
content: Quote from: woox2k on September 18, 2024, 06:49:06 amYour is going to be a bit worse because you are not using the gold plated probes.I'll do a demo video in a few hours.

author: woox2k
author_rank: Regular Contributor
timestamp: September 18, 2024, 07:01:06 am
content: Quote from: EEVblog on September 18, 2024, 06:54:13 amThat was intentional to make my example more clear. With proper gold plated probes the issue is not so apparent but still possible to make "scratchy" sound by touching the probes very lightly. While it might be faster it's still a bit earsore to hear those scratches. When measuring real circuit boards the contact is rarely as good as two gold plated probes touching eachother. Initially i noticed this "odd behaviour" with original gold plated probes. I was probably biased though because i had already used BM786 quite a lot at work and knew how it should sound.But it starts to seem that this is indeed intentional change by Brymen with v11 firmware... Interesting! I wonder what drove them making that change? The old "latch timing" was already fast enough to do "drag testing" to see grounded/shorted contacts. This one might be better in some corner cases but overall sounds bit cheap.... To a point i really thought this is a fault and inspired me to make this thread.

author: floobydust
author_rank: Super Contributor
timestamp: September 18, 2024, 07:34:53 am
content: Is this related to the BM786 electromagnetic buzzer issue? The bonehead that put it right on top at the xtal and sensitive ADC pins, which caused noise to get in, and I remember the fix was a metal shield to be put on the buzzer.edit:https://www.eevblog.com/forum/testgear/new-eevblog-bm786-multimeter/msg3608153/#msg3608153edit2: apparently I am wrong, the shield is for the magnet strap holder although I remember otherwise.

author: woox2k
author_rank: Regular Contributor
timestamp: September 18, 2024, 08:00:45 am
content: Quote from: floobydust on September 18, 2024, 07:34:53 amCurrently it seems to be a new setting in firmware, not in hardware. Let's wait until Dave has had time to investigate it. He did confirm that FW v11 meters have something differently configured. We don't know if the boards themselves have been significantly updated as well or it's all just in firmware. It being a firmware thing is kinda worse though, in that case there will not be a hacky workaround for people who prefer cleaner beep.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 09:01:25 am
content: Yep, confirmed. 78611 is different.I checked and Brymen didn't send me the 78611 firmware file, so I can't verify if the hardware makes a difference, but I'd be stunned if it did.

author: J-R
author_rank: Super Contributor
timestamp: September 18, 2024, 09:01:45 am
content: The metal shield was to prevent the Brymen magnetic hanger option from causing the speaker to be muted.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 09:40:09 am
content: Quote from: J-R on September 18, 2024, 09:01:45 amCorrect. It didn't impact the measurements.

author: woox2k
author_rank: Regular Contributor
timestamp: September 18, 2024, 09:48:41 am
content: Quote from: EEVblog on September 18, 2024, 09:01:25 amYAY, my meter is not faulty afterall!It would still be interesting to hear Brymen response on this. While technically the faster beep might be better, it's significantly different than it used to be on the same models. This can create some issues in a place that has hundreds of those meters purchased from different times...I can live with that but honestly i would prefer the slower beep. This was one of the (many) reasons i bought this meter. As in, it seemed perfectly balanced between two worlds, being fast enough to be useful and not so fast that the sound is messed up. My last meter did not have any latching on the sound, even the volume depended on the contact quality and i grew to hate that scratchy sound even though it too was very fast to respond.

author: J-R
author_rank: Super Contributor
timestamp: September 18, 2024, 07:02:43 pm
content: I personally don't like the scratchy sound either. One solution: Dave can offer firmware version flash options in his store at an extra charge.

author: EEVblog
author_rank: Unknown
timestamp: September 18, 2024, 11:32:43 pm
content: Quote from: J-R on September 18, 2024, 07:02:43 pmPossible, but postage is a killer.

author: J-R
author_rank: Super Contributor
timestamp: September 19, 2024, 02:00:55 am
content: Quote from: EEVblog on September 18, 2024, 11:32:43 pmI mean as part of the initial purchase. Take it out of the box, flash it, then ship it.

author: woox2k
author_rank: Regular Contributor
timestamp: September 19, 2024, 07:05:51 am
content: Quote from: J-R on September 19, 2024, 02:00:55 amAt least with Brymen meters Dave doesn't handle every single meter that is sold globally! They come directly shipped from Brymen to resellers around the globe. One option would be to give resellers the option to reflash firmwares but that will not happen (most would not bother anyway) Brymen itself cannot do that because it would be nightmare to keep track of all that stock of different firmware versions. Best solution would be to release firmware files so that users could flash it themselves but sadly that will not be a thing either.

author: EEVblog
author_rank: Unknown
timestamp: September 19, 2024, 07:06:10 am
content: Quote from: J-R on September 19, 2024, 02:00:55 amIf someone wants to order a special unit then I can flash in 78609 firmware.

author: EEVblog
author_rank: Unknown
timestamp: September 19, 2024, 07:07:49 am
content: Quote from: woox2k on September 19, 2024, 07:05:51 amThere are only two dealers, Welectron who order direct from Brymen, and Simon from Sparky Labs who orders from me.I handle all other global shipments from my lab here.

author: woox2k
author_rank: Regular Contributor
timestamp: September 19, 2024, 07:13:59 am
content: Quote from: EEVblog on September 19, 2024, 07:07:49 amWhoops, sorry. Apparently you are a hell of a lot more involved in handling those meters than it makes sense! Nice! That doesn't help people around the EU though (or the people who already have purchased the meter)... Meters sold by Welectron have not been upside down at your place(OT: How do you guys keep electrons in your stuff when they are upside down all the time?) Ordering one directly from you would probably cost an arm and a leg, plus a large amount of money. Same with sending it to you in order to get it flashed and shipped back...

author: J-R
author_rank: Super Contributor
timestamp: September 19, 2024, 09:24:29 am
content: I strictly was positing the concept that in Dave's online store (https://eevblog.store) he could offer an option where the buyer could select any firmware they wanted for their BM786 for a nominal fee.The solution to high shipping charges is to plan ahead and order up a few things at once, spreading out the cost per item.

author: floobydust
author_rank: Super Contributor
timestamp: September 19, 2024, 05:51:33 pm
content: Is the hardware mod relevant?https://www.eevblog.com/forum/testgear/bm789-continuity-behaviour/msg5108199/#msg5108199I would guess it adds an RC filter to the DMM IC comparator input and lower continuity response time.I did see a true "latching" continuity tester project, it uses a flip-flop to detect and latch, you have to manually reset it.It seems to be used when working on long wire runs, and in cars etc. where you are working far away from the multimeter searching for a short-circuit.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 19, 2024, 10:10:57 pm
content: Quote from: J-R on September 18, 2024, 07:02:43 pmYou have the scratchy sound only when you have and lose coninuity rapidly. If you touch the probes slowly you wouldn't hear the scratchy sound right?

author: EEVblog
author_rank: Unknown
timestamp: September 20, 2024, 12:42:44 am
content: Quote from: BeBuLamar on September 19, 2024, 10:10:57 pmYes, if the contacts are good, I demonstrate this in my video.