BM786 Switch Issue - Page 1
Forum section: electronics / testgear

author: J-R
author_rank: Super Contributor
timestamp: March 17, 2021, 05:45:30 am
content: WHAT, you didn't fix either of them?FYI for people reassembling a BM78x, the top corners of the PCB must first go underneath two plastic tabs molded into the bottom case.

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2021, 06:48:05 am
content: What's this?(also note dirty black line on the PCB above it)Edit: Another view...(note that it's in line with the Ohms range)

author: tautech
author_rank: Super Contributor
timestamp: March 17, 2021, 07:08:04 am
content: Good spotting Fungus.

author: DenCraw
author_rank: Contributor
timestamp: March 17, 2021, 08:30:25 am
content: What happen if you switch with the tester tips on hi voltage in that model?can you burn a trace?just because is some carbon there... a question for Joe Smith... hehe

author: station240
author_rank: Unknown
timestamp: March 17, 2021, 09:28:16 am
content: Best guess that hole in the switch contact is the result of:A. A bubble in the source PCB material that popped and was removed during etching.ORB. A hole in the PCB that got bigger during etching.It's curious that part of the gold plating has also been ripped off.Makes me suspect that part of the copper wasn't clean, and the gold didn't bond properly.I'm sure one of the PCB companies have seen this sort of thing before.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 17, 2021, 12:19:52 pm
content: Fungus finds the fungus..."... and it's in ohms range so you would never get high enough current passing through the uh input protection resistors here and the PTCs to cause some sort of ridiculous you know arching of like a across that contact. Its just its just not possible"At the rated voltage (1KV) it certainly is possible to draw an arc large enough to damage the contacts. I had made a video to demonstrate this after anther member had damaged a 121GW. While you should never rotate the function switch with the meter connected to an active circuit, a few of us have bad habits. Mix that with a little HV.....Brymen had sent me one of the early prototype meters. I wonder if I could replicated this hole....

author: EEVblog
author_rank: Unknown
timestamp: March 17, 2021, 12:30:17 pm
content: Quote from: joeqsmith on March 17, 2021, 12:19:52 pmExcept that's not what happened here.The fault was there out of the box, this is not a used meter, and there is no charring.It's a physical damage issue, not electrical.

author: Fungus
author_rank: Super Contributor
timestamp: March 17, 2021, 12:32:38 pm
content: Quote from: joeqsmith on March 17, 2021, 12:19:52 pmI saw it right away, didn't even pause the video.I wonder if you could fill the hole with solder paste and warm it up to fill the hole. It wouldn't last forever but it could make the meter work again.Google says there's such a thing as gold solder paste:https://www.google.com/search?q=gold+solder+pasteI see 14ct and 9ct variations. Not as cheap as lead but cheaper than a new BM786.(I volunteer to try it if you send me the meter.)

author: joeqsmith
author_rank: Super Contributor
timestamp: March 17, 2021, 01:32:15 pm
content: Quote from: EEVblog on March 17, 2021, 12:30:17 pmI would have no idea how the meter had been treated or what happened in this particular case. When the 121GW was damaged, the owner said the meter had not been exposed to high voltages. You posted a similar comment back then about the input which was the catalyst for the video. Of course, we did eventually get the real story in that case.Quotehttps://www.eevblog.com/forum/testgear/eevblog-121gw-discussion-thread/msg1598122/#msg1598122It may be difficult to trace it down as the evidence was destroyed. With that area missing, it went somewhere. If the wiper welded to the pad, I could see it tearing off a small bit. As the switch is rotated, any damage to the wiper may have been swept away.

author: floobydust
author_rank: Super Contributor
timestamp: March 17, 2021, 07:40:38 pm
content: The PC board has such bad scuffs and scratches on it, around the rotary switch area. Was there a gorilla skateboarding on it?Aha - on the switch pads, there's several other dimples (pothole in the making) as I can see pogo-pins have poked these switch pads too hard. Look at the innermost ring's pads pt. 2 at around 07:46 - all indented by test pins. I'd say the wrong pogo-style is being used - sharp point? NO. Second part of my hunch, also explains why the damage might be in the same location(s) on the other problem PC boards - the test fixture is trashing the boards. They might have a crown pogo there. Oops.Dave, look at the PCB on the other boards with the Ohms cutting out problem, see if the same location pothole is there.I am not a fan of this style of rotary switch, basically a copy of 1989Actron patentin ANENG, Mastech, Uni-T too although they use copper wipers (no gold). The design ends up with too much force from the wipers and you can see the PCB is worn at the south-east outer rings, so the rotor is not sitting parallel to the PCB, it's crooked for another reason.When will Asia improve and use phosphor-coated brass dual cantilevers? Quit copying 32 year old tech already.edit: I notice the new UT61E+ at least copied Fluke's detent spring arrangement, four cams. Those usually feel really good vs ball bearings w/hard springs. Progress.

author: Algoma
author_rank: Frequent Contributor
timestamp: March 17, 2021, 08:58:43 pm
content: The meter did work, provided it was left alone when taking measurements.Out of the box, on the Ohms range, very light tapping, bumping, squeezing or flexing the meter would cause the reset behaviors as noted in the video. It was a behavior that improved with use over a few days (Likely the initial wiper contamination wore off?).There was no issue switching between modes, only other issue was the two beep-lit modes could Alarm intermittently as if measuring open/short faults with nothing connected, at first very random at first, but it became more functionally reliable over a few days of use. (again, likely switch wiper contamination on those two modes).There was minimal use of the meter, besides basic low voltage testing a few 19v laptop power supplies, and out of circuit diodes and resistors.Initially pressing any of the buttons or putting general pressure anywhere on the case would cause the reset in the Ohms mode. It improved with use over a few days, until the reset could only be caused by nearly directly manipulating the dial as seen in the video, or putting direct pressure on the body of the meter such as firmly pressing, squeezing or twisting on the body of the meter.

author: raftronik
author_rank: Contributor
timestamp: March 18, 2021, 06:52:34 pm
content: Why power switch has to be on rotary switch not separate switch. My Metex has separate power ON OFF switch, it is very usefull.

author: Kartika
author_rank: Regular Contributor
timestamp: March 25, 2021, 07:40:42 pm
content: Hi, I'm just receiving it and I couldn't resist opening it ... this stinks of production abuse. why? how is that possible ,,, such a good multimeter with a large and inadmissible omission ...

author: floobydust
author_rank: Super Contributor
timestamp: March 25, 2021, 07:56:57 pm
content: Um, what is the omission you are talking about?I just see a gorilla used 180 grit sandpaper on the rotary switch portion of the PCB. They should use an angle grinder instead. WTF are they doing. Those scratches are terrible on thin copper.The rotary switch tracks don't look gold plated? Maybe they are sanding off the ENIG and plating something else there. edit: nope, the via's still are gold. So they have some selective plating going on here.I don't see pogo-pin indentations anymore.P.S. - If you clean the PCB with IPA, don't forget to lubricate the switch portion.

author: Kartika
author_rank: Regular Contributor
timestamp: March 25, 2021, 07:59:49 pm
content: Quote from: raftronik on March 18, 2021, 06:52:34 pmyes, very useful. increases switch cycles

author: Kartika
author_rank: Regular Contributor
timestamp: March 25, 2021, 08:07:53 pm
content: Quote from: floobydust on March 25, 2021, 07:56:57 pmwhich lubricant do you recommendthis is not burned but the layer is separated ... i belive bad procesing

author: floobydust
author_rank: Super Contributor
timestamp: March 25, 2021, 08:33:16 pm
content: The lubricant to use... that discussion will start a holy war here. Best to ask Brymen what they suggest.What do the wipers look like on the BM786 rotary switch? as far as metal and plating.I found mineral oil is commonly used on the PCB, Fluke I believe uses that. A contact cleaner and lubricant withpolyphenylene ether (PPE)is the only thing stopping oxidation from bad connections, when a switch has poor metallurgy or p[oor mechanical design (low force).Is that PCB pothole on your multimeter? I don't see it in your first pics so I'm a bit confused.

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2021, 08:41:57 pm
content: Quote from: Kartika on March 25, 2021, 08:07:53 pmYep it's another dud one like this one Fungus spotted earlier.Ask Dave to replace it.

author: bd139
author_rank: Super Contributor
timestamp: March 25, 2021, 08:45:34 pm
content: I bet at the factory they had a couple of QC failures and identified the cause as contact plating issues. So they just sand the top of the board now because it made one work. Never trust a QC engineer. They’re almost as bad as software engineers.Either way screw that - they’re added to my vendor shitlist now. Nothing should be shipping like that.

author: AVGresponding
author_rank: Super Contributor
timestamp: March 25, 2021, 09:16:19 pm
content: I believe the picture Kartika linked in their last post is simply an enlargement of the original one that Dave linked, with their (Kartika's) opinion as to the cause.It is not good to see those scrubbing marks though, very disappointing from a manufacturer of Brymen's reputation.

author: Kartika
author_rank: Regular Contributor
timestamp: March 25, 2021, 09:18:39 pm
content: Quote from: floobydust on March 25, 2021, 08:33:16 pmis not just my comment from the post before, sorry

author: Kartika
author_rank: Regular Contributor
timestamp: March 25, 2021, 09:24:31 pm
content: Quote from: AVGresponding on March 25, 2021, 09:16:19 pmthis is like cramp processing ... it worries me, and I only hope this is a mistake ...

author: joeqsmith
author_rank: Super Contributor
timestamp: March 26, 2021, 12:38:51 pm
content: Looking at the board, this pad is indeed the one used to select the high speed clamp when in ohms. Looks like a 1.3K PTC and a 1K, typical. I took some decent before pictures of this area and will attempt to reproduce the picture shown.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2021, 12:41:49 am
content: All of the meters I looked at had these scratches in the switch area. I didn't ask them about it. Agree that it looks poor but it didn't seem to have much of an effect on the meter I life cycled. If you watch that video, the meter was still working fine after that test. Many meters that started out with smooth boards were ground to dust....Here are a couple of pictures showing this area before I subject it to some high voltage with the meter set to ohms.

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2021, 01:15:28 am
content: I don't know if it has been mentioned before, but it looks like your picture is missing the same chunk off the end of the trace as the other meter that failed?

author: floobydust
author_rank: Super Contributor
timestamp: March 27, 2021, 02:20:05 am
content: There's nothing physically wrong with that PCB portion - it's just bad PCB CADD layout.You have rectangular-ended switch polygons, rounded-end traces and soldermask connecting there, so it looks wonky.Many traces exiting the rotary switch leafs are done wrong - they should exit radially. Otherwise you get overlap and extra scuffs. It's not a great switch PCB layout IMHO.From the way the DMM cuts out when the switch is wiggled on Ohms, I suspect power being shorted out vs open circuit?P.S. I wonder if you can even do this switch design in Altium, or you have to draw it in AutoCAD and import the switch portion?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2021, 10:33:03 am
content: Quote from: bdunham7 on March 27, 2021, 01:15:28 amInteresting is that it would seem that this area of concern for you may actually be a way to improve the design of meters. Consider the attached picture showing the BM786 after completing a 50,000 cycle life test on the switch. Not Dave Jones 50K but full CW/CCW making one cycle. Or 100,000 DJ cycles. Notice in cases where the mask is removed in area around the contact's leading edge, we see some rounding off where in this case, we start with a smoother transition and less wear.Even with scratches the meter held up very good to this test compared with others I have looked at. Low quality meters are ground to dust and if we want to talk about poor layouts that actually hurt the performance, lets at least mention the end results of placing a via in the center of the switch contacts.

author: AVGresponding
author_rank: Super Contributor
timestamp: March 27, 2021, 01:45:36 pm
content: Quote from: joeqsmith on March 27, 2021, 12:41:49 amGranted it probably doesn't affect switch life noticeably, but it does indicate a degree of hand finishing which is as we all know something you prefer to avoid due to cost, variability of results etc.Can't be good for the solder mask, and there has to be at least a small risk of pinging off a component or damaging a trace.It begs the questions, why do Brymen consider it necessary? What problem with the automated fabrication process is this an attempt to remediate?

author: Algoma
author_rank: Frequent Contributor
timestamp: March 27, 2021, 02:48:12 pm
content: Looks like about 5 quick scrapes with fairly coarse abrasive.I would think A simple scrub with a fine steel wool would put texture and shine on the pads without scraping off vast gouges across the solder mask.The scratch pattern looks like they're using an edge of a heavy grit sanding block that barely fits into the given space of the already populated board.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2021, 04:35:33 pm
content: Like I said, I never asked them about the scratches and without taking that first step, I would have no way to who, why or when it was done.Getting back to my comments about HV and the ohms function.https://www.eevblog.com/forum/testgear/bm786-switch-issue/msg3516068/#msg3516068https://www.eevblog.com/forum/testgear/bm786-switch-issue/msg3516184/#msg3516184First, Brymen supplied four different meters. One meter was a non-functional, incomplete prototype. This is the meter I used for this test. As you can see from the pictures, the layout and scratches are similar to what was released. The meter was supplied with no wiper contacts. Sorting through the junk pile, I found a wide contact that came close to fitting. Of course, this is different than the contacts supplied with the meter. I used my kill-u-dead power supply which you may have seen blow one of my HV 400mA fuses.Looking at the attached pictures, you can see how the wiper contact did not ride down the center of the pad and is off to one side. We can see that the heat was enough to delaminate the board. What is interesting is the size of the area of damage. Had the contact been centered, would we even see the delamination? Maybe not. I would even suggest that the plating could fail some time later. By chance, it looks like it made better contact on the other pad and there appears to be no damage. I tested the two transistors that make up the high speed clamp (Q4&Q5) prior to running the test and after. The both appear fine. I would have expected that but it's good to know.Will the PTC and surge rated resistor limit the current enough to save the switch contacts under all conditions? I would say no.Could the input signal be within the range of the meter and damage it? I would say yes.Could the PCB be damaged without there being any damage to the front end and clamping circuits? I would say yes.Could the damage be such that it creates enough heat to delaminate the PCB? I would say yes.Are there sources of HV/HC that could do this level of damage that are common? Seems like the MOT is a common source..Again, I have no idea what happened in this particular case. I do find it odd that the failure just happened to be on one of the modes using the high speed clamp. That the delamination is only on one spot of the entire board. That spot just happens to be where the wiper contact would sit when the ohms mode is engaged.

author: Algoma
author_rank: Frequent Contributor
timestamp: March 27, 2021, 05:54:16 pm
content: I can assure you, this meter only encountered light usage in a computer repair shop before it was set aside for exchange from Dave due to the noted issues as before. The replacement meter has worked flawlessly for weeks now.the original meter in question was only subjected to the following list over the few days it was out of the box:1) DHL's shipping process, they certainly did their best effort to indent the lower right corner of the the packing box.2) Dell Laptop 19.5VDC 5A power supply, all tested good.3) RH05020R00FE02 20Ohm 1% Vishay Dale Chassis Mount Load Resistor4) CMF601K0000BHEB 1K 1W 0.1% Vishay Dale Axial Resistor5) CMF60100R00BHEB 100Ohm 1W 0.1% Vishay Dale Axial Resistor6) HEATHKIT IN-3117 DECADE RESISTANCE KITHighest voltage nearby would be 120v Mains power bar +- Static electricity .. at best.I'm neither qualified or experienced enough go anywhere near the limits of a brand new meter I paid good money for, especially poking conductive things towards dangerous energy sources, on any range. Your original testing videos assisted in the decision to select this meter as a safe and well qualified meter for my usages. I'm simply a Network Engineer with curiosity about the foundations of the technology I work with. Not an electricianThe minimal usage it encountered is very unlikely to have caused any such damage to the trace, unless it was some form of high voltage qualification testing done at the factory.

author: Fungus
author_rank: Super Contributor
timestamp: March 27, 2021, 05:56:30 pm
content: Quote from: bdunham7 on March 27, 2021, 01:15:28 amWho says it's missing a chunk? In Dave's videoallthe traces have square ends, even though there seems to be a round end on the PCB.The trace at the top looks like a boolean union between the exposed gold trace (with square end) and the non-exposed trace under the solder mask:

author: joeqsmith
author_rank: Super Contributor
timestamp: March 27, 2021, 06:28:02 pm
content: Quote from: Algoma on March 27, 2021, 05:54:16 pmAs I have said, I would have no way of knowing what happened. For all I know, the meter was left sitting out and someone borrowed it for a test run. I wasn't there, I didn't receive your meter to evaluate and looking at it now would be rather pointless as any evidence left would have been taken care of by the end of a metal blade. All I can do is present data that shows that it is possible to delaminate the PCB while in the ohms mode while injecting a signal to the inputs of the meter as well as point out other details we can see from the video and pictures.

author: Algoma
author_rank: Frequent Contributor
timestamp: March 27, 2021, 10:00:21 pm
content: Yes, and I'm defending the point that this was NOT caused by suicidal abuse of the multimeter. the issue was present within the first turn of the dial with no leads attached. This case was fully sourced from the manufacturer.I state clearly, that it is false, slanderous hearsay to claim that in this case the meter was abused, and the evidence hidden in this case. Dave's blade left far more scratches in his video than any other markings on that trace,.

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2021, 11:52:14 pm
content: Quote from: joeqsmith on March 27, 2021, 10:33:03 amOK, from that angle I can see how the traces intersected and I see the worn triangle of soldermask on the life-cycle tested meter.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2021, 01:52:48 am
content: Quote from: Algoma on March 27, 2021, 10:00:21 pmI have made no false claims about what happened to your specific meter. I have stated multiple times that I would have no way of knowing.Quote from: joeqsmith on March 17, 2021, 12:19:52 pmWhat I have done is conducted a simple test to see if the original statement from the video was true or not and presented my findings. I'm sorry that makes you become defensive. It shouldn't.

author: Algoma
author_rank: Frequent Contributor
timestamp: March 28, 2021, 01:58:49 am
content: @joeqsmith I do apologize.Your work and testing is valuable to the community, and this in depth investigations indeed this shows what types of damage can occur to a meter if mishandled. Thank you for all the work you put into testing these meters.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2021, 02:07:21 am
content: Quote from: bdunham7 on March 27, 2021, 11:52:14 pmYou can see how this leading edge can cause problems. I think you may be onto something. Then again, when we look at the Fluke 87V (damage 2), we can see how the design of the wiper contact can also have an effect on wear. There is an art to getting the switch right.

author: EEVblog
author_rank: Unknown
timestamp: March 28, 2021, 10:28:02 am
content: Quote from: joeqsmith on March 27, 2021, 06:28:02 pmJoe, why are you getting involved in this way? Algoma is the owner of the meter in question, there is no need for speculation like this, he has categorically stated that this happened out of the box, he contacted me the day he got it and tried it. There is no need for speculation here on your part, it is not helpful. This is a factory fault.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2021, 03:01:20 pm
content: Quote from: EEVblog on March 28, 2021, 10:28:02 amBecause you chose to make it public and make a claim which I questioned the accuracy of. I'm sorry you feel that my attempt to substantiate your claim wasn't helpful. If you like, you may remove the posts if you feel that strongly about them. Personally, I like being data driven but its your site.https://www.eevblog.com/forum/testgear/bm786-switch-issue/msg3516068/#msg3516068https://www.eevblog.com/forum/testgear/bm786-switch-issue/msg3532326/#msg3532326

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2021, 04:39:27 pm
content: Quote from: EEVblog on March 28, 2021, 10:28:02 amThat still leaves the question of what happened at the factory--and how likely it is to be a common issue. I suspect that it is actually not going to be a common issue, as the most likely thing I can think of that would cause this would be technician error or equipment malfunction during the calibration process.I have had three incidents in the past year while repairing multifunction calibrators. One was my error, I fed my best DMM 900VDC while in ohms range (no harm done), one was a calibrator that would surge a bit while settling on AC and it went above 1000VAC enough to cause the DMM clamping to activate, which then tripped the calibrator overload (again, no apparent harm--I think). I started using 'disposable' meters for initial checks and just last week I was testing one at 1000VAC/1kHz when I looked over to see the disposable meter of the week, an old Fluke 8800A, reading 1435 volts! Again, amazingly, nobody died.Since the ranges have to be selected manually during calibration, how easy would it be for that tech to select 1kV and then realize that the selector is still in ohms? Or, to turn the knob to ohms and then realize that the calibrator is still putting out 1kV? Even if the process is more automated, there's still ways that something like this could go wrong.

author: floobydust
author_rank: Super Contributor
timestamp: March 28, 2021, 08:05:47 pm
content: The Ohms switch ring has what appears to be a runt which may be aggravating things, looks too short compared all others, not much overlap? That might be a design issue showing up with manufacturing tolerances in production.You'd have to remove the detent mechanism and turn the switch side to side, to see how much slop there is, where it still works.It's extra hard doing PCB layout with mechanical constraints- tolerances, moulding needs, etc. Any disconnect between the MECE's and EE's can cause grief.I suspect the switch cannot be drawn in the PCB CADD software, so it is drawn in something mechanical (AutoCAD) or wherever the switch mech is being done for the plastics.Then it's imported into the PCB layer or Gerbers. You can tell because many traces seem to make a wonky exit from the switch leafs.I have seen this (import as graphic) to achieve oddball geometry/shape copper, but it's a total nightmare for netlists and error checking.Regardless, I'm sure Brymen is on it.

author: EEVblog
author_rank: Unknown
timestamp: March 29, 2021, 01:12:18 am
content: Quote from: bdunham7 on March 28, 2021, 04:39:27 pmAs several people have pointed out, I think it's most likely a one-off issue involving the PCB manufacture. There is no evidence it's been burned or pitted away by a high voltage arc in testing. And such testing is usually automated.It looks like there was a copper lamination issue that ultimately resulted in the copper tearing due the switch contact movement.

author: EEVblog
author_rank: Unknown
timestamp: March 29, 2021, 01:15:35 am
content: Quote from: joeqsmith on March 28, 2021, 03:01:20 pmNo, it's you questining the owners account that I had a problem with.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2021, 03:13:27 am
content: Quote from: EEVblog on March 29, 2021, 01:15:35 amAs I had stated in most of my posts, I would have no idea what happened in this particular case. I can only post on what I see and heard in your video. Like I said, feel free to pull it all if it bothers you too much or just don't respond to them.

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2021, 03:39:20 am
content: Quote from: EEVblog on March 29, 2021, 01:12:18 amMaybe so, and if it is (hopefully) truly a one-off, we'll likely never know. I've never seen a defect like that on an unmolested PCB trace and that looks like a decent board. It typically would take bit of work to tear off a chunk from the middle like that unless there was something like a buried via underneath causing some stress--and since it looks like a 2-layer board, there shouldn't be one.An electrical event wouldn't need to cause much arcing to cause a bit of localized heating. The next time I have a calibrator fired up I'll see how it welds.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2021, 01:00:56 pm
content: "... unless there was something like a buried via underneath causing some stress--and since it looks like a 2-layer board, there shouldn't be one. "No buried vias. There's nothing in that area.Maybe a SEM could have detected something. Even with the PCB in the current state, it could be sectioned. Both may tell you if there was any sort of arc or heat damage.I don't know anything about modern calibration equipment but wouldn't expect them to have enough output capacitance or current in the HV setting to do much. Then again, it may not take a whole lot to damage the board. It will be interesting what you find.Maybe post the model, open circuit voltage, short circuit current, output capacitance or use a 2.3ish kohm load and watch it with a scope. The more details you can provide about your setup, the better.

author: Fungus
author_rank: Super Contributor
timestamp: March 29, 2021, 07:52:05 pm
content: Quote from: joeqsmith on March 29, 2021, 01:00:56 pmMaybe a bug crawled into the PCB plant and got stuck under the copper. I'm sure it happens.The good thing is that this definitely isn't a systemic production fault. It's a one-off that got through quality control by needing a user to press the dial just right.

author: EEVblog
author_rank: Unknown
timestamp: March 29, 2021, 09:41:13 pm
content: Quote from: Fungus on March 29, 2021, 07:52:05 pmI'm putting it down to a PCB manufacturing fault which was then exacerbated by the switch contact. Not the first time I've seen etching pits in PCB traces.And I agree with Joe, I doubt any multimeter calibrator has enough output capacitance or current capability to do any serious damage. And I greatly doubt HV on the ohms range is a production test they perform, that's a system qualifcation test. And these tests are usually semi automated.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 30, 2021, 12:13:24 pm
content: I provided Brymen with a link to this thread along with some addition information and have asked about the scratches. Maybe we can get some insight.

author: bdunham7
author_rank: Super Contributor
timestamp: March 31, 2021, 05:42:43 am
content: Quote from: joeqsmith on March 29, 2021, 01:00:56 pmOK, maybe my theory is a bit far-fetched, but here is what I have. I don't have time/space to haul in a calibrator to do any extensive testing right now, but I went out in the garage and just plugged one in on the floor and tried it with some 1/2 watt carbon film resistors. This is a Fluke 5101B Multifunction Calibrator, 1100VAC/VDC with a rated output current of 6mA, the output protection seems to kick it out somewhere in the 8-10mA range. The HV drive is a low voltage ~35VAC power amp driving a very large transformer, followed by a bridge and capacitors for DC. Total capacitance 0.66uF, so no spot welding is likely.I tried it with 2.7K of resistance, but it instantly tripped off. After a little experimentation, I put in a 120K resistor, set it for 1kV/1kHz and got some action. There would have to be some pretty specific circumstances for this to cause the damage to the PCB, so perhaps it's not all that likely. OTOH, this is just one test on one specific calibrator.Sorry, it has to be in a .zip file to upload...

author: dcac
author_rank: Frequent Contributor
timestamp: March 31, 2021, 10:33:29 am
content: You would think if the hole in the PCB was created/worsened by any HV event in the meter - some kind of damage/evidence should also be visible on the corresponding spring contact/dimple.I've watched Dave's videos but I don't think he ever looked at the contact spring.

author: EEVblog
author_rank: Unknown
timestamp: April 11, 2021, 05:25:38 am
content: Quote from: dcac on March 31, 2021, 10:33:29 amI did, and there is no evidence of any damage.

author: HAO
author_rank: Newbie
timestamp: April 10, 2023, 04:05:29 am
content: I have the same problem with my Brymen BM789. Does anyone know how to fix it ?

author: J-R
author_rank: Super Contributor
timestamp: April 10, 2023, 08:58:51 am
content: Your issue seems different?On my BM789 I get that voltage reading with approximately a 53.22k Ohm resistance.Maybe try opening it up and checking for contaminants?

author: HAO
author_rank: Newbie
timestamp: April 10, 2023, 04:01:04 pm
content: Quote from: J-R on April 10, 2023, 08:58:51 amHere is my issue :https://m.youtube.com/shorts/QUmqFHYuMGI

author: Pokey44
author_rank: Newbie
timestamp: April 12, 2023, 07:22:05 am
content: I have what I think to be the same issue on my BM786. I've almost never used it. It's outside the return ability on Amazon (bought in October last year) and it wasn't clear to me whether it is warrantied. I've had a hard time getting info from the seller on Amazon.The issue for me: it will sometimes turn on when rotating the wheel, usually a good halfway through the settings, but many times it will never latch on again or do so very unpredictably once it's powered off again. Maybe it is the contacts, or maybe it is the latching mechanism that Dave investigated in the first video he did, but either way I'd really like to fix it as I never got around to making it my main meter. I did try to clean the contacts and the rings with basic IPA but it made no difference.I hope it's not a dud!

author: J-R
author_rank: Super Contributor
timestamp: April 12, 2023, 09:30:02 am
content: In both cases, if you cannot get any warranty support, then I would start by experimenting with the spring contacts under the selector switch.Inspect the PCB under a magnifying glass or similar for any bad solder joints or damage.

author: Pokey44
author_rank: Newbie
timestamp: April 14, 2023, 02:41:55 am
content: Yeah, I already inspected my contacts under my scope and they look good and clean, same for the springs. It's very disappointing to have bought a $250 meter that I can't get any support on. I'm ready to just buy a really nice Fluke and be done with it.

author: J-R
author_rank: Super Contributor
timestamp: April 14, 2023, 04:00:18 am
content: I think on the spring contacts I'd mostly be concerned with making sure they are springy enough to push on the PCB under all conditions. If you remove the top cover and press the remaining portion of the selector switch towards the PCB, does that change the behavior?Any issues with power delivery? The BM78x battery holder has contacts that could be flaky.Was the seller on Amazon Dave or someone else?

author: Pokey44
author_rank: Newbie
timestamp: April 18, 2023, 10:37:43 pm
content: Thanks for the reply. I bought it from seller "EEVBlog" on Amazon. I have contacted the seller a few times. They did respond once, and told me to just have Amazon deal with the return... but I can't return it, it's been too long (ordered in October 2022), and follow-up questions for support/warranty went unanswered. I don't know if it's Dave though, maybe someone else manages it? I'm guessing if it *is* him, he probably sends a box of them to Amazon for fulfillment and they do the rest.I didn't see any issues with power delivery, but also powered it with a bench supply to be sure. Same flakiness.I also suspected the springiness of the springs and gave it a good push as I turned which didn't seem to make a difference.What I often see is that on a "cold start" after its been sitting a while, it will sometimes power on when the rotary dial hits a few positions in (usually the 3rd). Once it is latched on, the dial works fine to switch between all the modes. Once I turn it back off, it's a crap shoot whether it wants to start up again -- and again it has to be turned a good ways before it kicks on, never on the first position. However, eventually, it dies entirely and will not power on at all in any position. After it sits a while, though, I can manage to get it to turn on again by hitting the 3rd-4th position or so as before. And the cycle repeats. Pressing or pulling on the knob to increase/decrease spring pressure makes no difference that I can tell.I'm a hobbyist/tinkerer grade guy, not a EE, and still learning. After watching Dave's videos diagnosing different things on these, he mentions there's a latching power-on circuit that he theorized could go bad. Maybe that could be it?

author: mwb1100
author_rank: Frequent Contributor
timestamp: April 19, 2023, 06:41:10 am
content: Quote from: Pokey44 on April 18, 2023, 10:37:43 pmFrom the last page of the manual:QuoteContact info is:BRYMEN TECHNOLOGY CORPORATIONTEL:+886 2 2226 3396FAX:+886 2 2225 0025http://www.brymen.cominfo@brymen.comIf you seek warranty assistance directly from Brymen, let us know how it goes.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: April 19, 2023, 06:38:30 pm
content: It is unfortunate to see the issue with your meter, it very well could be a power supply issue elsewhere in the meter, and not just the rotary selector switch. The mechanical vibration while turning the dial might just have trigger the power up/down condition.While I like my Bremen meters, the difficulties in obtaining post-sale service locally is the biggest drawback. Sending it back to Europe for repair is just not economically justifiable, or worth the time considering the paperwork you have to fill out.Fluke provides local repair service, along with lifetime warranty (kind of) for its higher end meters, which may justify its higher price for users who depends on their DMM for their daily jobs.Unfortunately, EEVBlog is just a distributor, other than an exchange for DOA, I think they will likely referred you back to Brymen for warranty claims.

author: Pokey44
author_rank: Newbie
timestamp: April 21, 2023, 12:41:17 am
content: Thank you. It's amazing I missed that on the last page of the manual. When I googled for info on the Brymen warranty I first was led to "brymenmeter.com" which turned out to be a reseller in Europe. The official site at Brymen.com didn't have any info on the warranty for this specific model either.I will definitely reach out and update here with any results.I guess if I had to do it again, I don't think I'd spend $250 on a meter that requires international shipping for warranty work. In the past I've worked with companies like Anthem (the AV company) that are based in another country and do their warranty work there, but they have a single domestic shipping point they use in the US to save customers the extra cost and effort. Not a bad setup when you can get it.

author: EEVblog
author_rank: Unknown
timestamp: April 21, 2023, 01:14:05 am
content: Quote from: NoisyBoy on April 19, 2023, 06:38:30 pmIf you purchase an EEVblog branded Brymen then I handle the warranty exchange from my own stock. Every other dealer should do the same.

author: floobydust
author_rank: Super Contributor
timestamp: April 21, 2023, 02:51:48 am
content: I'd rule out a problem with the two transistor power switch. It might be worth a quick measurement to make sure it's working or has a lazy mosfetI couldn't make out the SMD marking codes for them in Dave's videoEEVblog 1520 - Troubleshooting a Faulty BM786 Multimeterbut it's worth a check in the case the rotary switch is not the problem, it's just weak power causing erratic behaviour.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: April 21, 2023, 08:52:45 pm
content: If you like Brymen meters and domestic support, then you should get a Greenlee. You get local support, plus limited lifetime warranty, you will pay more, but not unreasonable. However, they don't have the 786 equivalent.I believe Brymen only warranty their products for 12 months. I hope you will get your issues sorted out soon.Quote from: Pokey44 on April 21, 2023, 12:41:17 am

author: Hydrawerk
author_rank: Super Contributor
timestamp: April 23, 2023, 08:59:45 pm
content: How common are switch (or other) issues on BM789 / BM786? I might want to buy one in future...

author: giosif
author_rank: Frequent Contributor
timestamp: April 23, 2023, 09:19:56 pm
content: [Just seen this thread]I am experiencing the switch issue with my new BM789 not even a week in, and I'm only an EE hobbyist (issues documented in the BM789 thread).

author: Pokey44
author_rank: Newbie
timestamp: April 27, 2023, 12:11:01 am
content: Quote from: EEVblog on April 21, 2023, 01:14:05 amThanks for your reply -- I bought it from "EEVBlog" on Amazon. Whoever it is, they aren't too keen on replacing the meter. They just told me to send it to Amazon and stopped responding. Amazon of course is not going to take it because it's outside the return period.As far as the Brymen contact I emailed them 6 days ago (info@brymen.com) with no response.

author: EEVblog
author_rank: Unknown
timestamp: April 27, 2023, 01:01:57 am
content: Quote from: Pokey44 on April 27, 2023, 12:11:01 amThat EEVblog is me. Amazon usually handles the returns. But I just checked messages on Amazon and it seems they didn't send me your latest reply that it was outside the return period. Perhaps because it had a link?You can return it to:EEVblog ReturnsPO Box 7949Norwest NSW 2153AUSTRALIAI'd like to look at what the issue is. Please include your details.

author: Pokey44
author_rank: Newbie
timestamp: April 27, 2023, 05:38:00 am
content: Oh thank you Dave, I'll send it over.I hate that I failed to fix it myself, but maybe there's something to learn here once you have it.