Brymen BM786 Switch Fault Investigation 

imagine finding a problem in your own product and publically posting it to the target market. HONESTY IS HIGH, I REPEAT HONESTY IS HIGH.

Thumbs up for the self tapper alignment pro tip. I've always done it like this so it's somewhat painful for me to watch people hastily cross threading the screws.

I'm betting that every BM786 owner is now wiggeling their switch like crazy....😅🤣

I see a lot of recalls in the near future...

There's a deep scratch or gouge in the contact pads on the first one. You need to take that apart and take a more careful look at them. I'm pretty sure the scraping is one of the wipers has a sharp burr or something like that, and is basically scratching off the metal layer on the PCB underneath it. That's why it made that horrible scratching noise, and why it started causing problems after being worked in a new position for a bit, and why it eventually caused the same fault after that transplant to the other meter as well... Could be wrong but that was my immediate thought already at 07:33 - stop and go frame by frame, look at the 2nd-outmost contact from the right of the screen - big ol' piece of copper ripped off from the contact. If you compare it to the 2nd meter at 17:59, on the right, you see no such missing patch in the track. Also at 08:08, the leftmost wiper, has metal shavings / dust all over itself, so I'd bet that's the one that has a sharp burr or edge somewhere.

Many years ago i had a board with a cracked via inside the board that had similar symptoms.

I sense a great disturbance in the force. As if hundreds of voices suddenly cried out " Wiggle, wiggle yeh".😁

7:44 is there a hole/missing a piece of the trace at the second last trace on the bottom? 18:18 it doesn't seem to be on the other LCD faulty meter.

Hey Dave! I just want to say something about the first meter. If you look at one of the contacts, their is a crack in one of the contacts. It could also be that the pressure needs to be changed on the actual dial switch part. The time in which you see the first meter contact is at 7:52

I want all of the companies I buy products from to do youtube videos of their product returns!

7:53 the 4th ring from the outside looks like the contacts get off the track, also look at the tracks in the middle. The soldermask might be slightly higher and lifts up the contact. I bet you cant reproduce this error if you wiggle the switch downwards.

The part dimensions can be changed very slightly depending upon the cooling time and cycle time of the machine at the time, or the parts could even be slightly warped if it was run too fast or there was a mould cooling fault such as an air lock in its water galleries.

Just wanted to mention that there is still some audio sync problem. You can see it nicely at 21:02 when turning the switch. Cheers

Remember when I tried to repair my old Sanwa pocket meter (used for 10 years), it got the same reset, it will happen when you turn the switch in-between selection, wriggle it also may cause the meter to reset, I guess some contact was not correctly shorted.

What you want to do with those self-tappers is tighten 'em till you hear the plastic crack, back 'em off a quarter turn, call the intern over to finish up while you go for coffee break.

One idea to check: the tolerance of how wipers are placed inside the plastic part. The part seems to be universal and the wipers are inserted according to the PCB layout of a concrete model. Maybe they are barely touching the traces. Look at the scratches on the PCB traces, especially at the Ohms axis.

I have had the Aneng AN870 meter for 3 years, bought for 1/3 of the BM876 price, I use it for repairs in the service center. It works flawlessly. This gives much food for thought.

The quick fix would be to increase the gaps between the wipe traces

7:53 second ring from the outside 7 o'clock looks like a cut through the contact.

Great vídeo!

Pretty sure I saw a crack in the left side of the switch circuit trace on the board Dave, right near the start of this video when you first opened it up and we're inspecting the board for production hairs🤣👍🇦🇺

Last month, my old DMM was acting up on ohms/diode/buzz. Took it apart. Sure enough there was gunk on the switch position.

on 7:40 there seems to be, on some angle, a crack in one of the switch traces, second ring from the outside, just above the white silkscreen label starting with S1.

Dave didn't let this problem ride for long...Hence, Part 2 next!

Han an Extech EX330 with the same problem when switched to ohms. Really annoying so had to replace it

When I pull that hard on my keysight I can get it to reset sometimes too... there is only so much space the contacts go out with enough pressure, if you pull that much out, its over. Also note that with these self tapping screws in plastic, the moment you screw them in a second time you make them so weak that you introduce an extra little play... I have had to glue in a lot of screws in my life to fix things by removing that little bit of play...

I would check alignment and also the force of the switch module down into the pcb.

Perhaps the PCB is bending when it is tightened in to the case plastic so the switch contact area won't be flat?

Isn't it weird that multimeters still use complex rotary switches? I don't think anything else does. Wouldn't it be simpler, better, and cheaper to switch everything electronically? Or do the potentially (pun intended) high voltages and currents make this impractical? Also, try explaining to your non-engineer manager that failure analysis doesn't mean just going with the first hypothesis. And that you need some answers to some simple questions like how many units have failed in the same way. I may just happen to be struggling with problems like this myself . . .

Hi Dave, I have a 15B+ Fluke (ordered from Aliexpress, paid about $100 AUD) that sometimes I turn it to VDC, and nothing happens. Only by turning it to the off position and then back on does it work. Wondering if you want to have a look at it (for a video or otherwise - you always seem interested in intermittent faults). I would want the meter back, however. Happy to pay postage both ways. Cheers, Andy

7:57 On the switch itself, on the side that faces the pcb are 4 numbered circles in the black plastic. Number 3 looks like it may be collecting some stuff... At least, that's what it looked like on video. There's something there, but it's hard to tell if it is sticking proud or not.

Is the BM786 a replacement for the 121GW which seems to be no longer available?

It is possible that something as simple as ambient temperature might affect how easy it is to trigger the fault if the part is marginal.

It is likely that the user dropped it and the impact struck the switch. How carefully did you look for hairline fractures? Can you tell where the contacts ride on the board traces (a little transfer pigment might help)? A little sandpaper or a file on those riser posts will likely improve operation. I also didn't like the springiness of the PCB and would reshape those board standoffs some. I would also deburr those screw holes. Alternately, there could be a flaky trace, solder joint, or via on the PCB.

The display error looks like the error I've had with multiple fluke meters. I fixed each one by simply cleaning the connector between the display and the (main) PCB with a bit of isopropile alcohol and a cotton swab. All the time the connectors looked just right before cleaning, still it was the solution

Maybe there's an issue with one of the case halves, causing the board to flex in such a way that it's not contacting right.

Dave, possibly a microcrack in the pcb? Or in another component? To much pressure could cause that!

My theory: Probably the posts where the screws come in from the bottom - screws cause the plastic to 'bloom' a little, and the plastic burr lifts the switch body.

Hey Dave. What’s the make/model of the keyboard doodad you’re using to switch the cameras about? Looks super handy. Thanks!!

Did I dream it or was there an amp-hour episode where you mentioned Bryman figured out it was a PCB tolerance issue and the fix was to ship out plastic spacer washers to raise the thin PCB up a bit?

Dave reinvents the click of death from Zip drives...

Considering that you went from one bad meter to two, I would re-check your assembly/handling process to make sure you're not introducing the problem.

Looks like it could be the part that holds down the contact wheel is not holding the switch down.

At some point you’ve got to call that your using un natural force on the switch. To me it appears something to do with the housing and board and switch tolerances. Something is not quite right causing contacts to separate more than the normal tolerances. I would assume all of them do it but some need more un natural force to make it happen.

I have a guess at what's happening (not necessarily what causes it though) I think that when you push the switch back it lifts the contact of the board just about to have nothing selected which causes the micro to panic and reset because there is nothing selected on the switch. The switch probably lifts off the board because of the tolerance stacking

My Uni-t is rock solid

Dave you're missing an 'r' on your streamdeck :)

Guess, mid watch: the drill alignment was off tolerance with the copper.

I got a extech ma 1500 and I been trying to just get the v accuracy to be more accurate @13, v so I calibrate it at 9.83 v from v refrence it's been a pain .so many variables

Could the PCB be cracked due to pressure from screws being tightened too hard or uneven case design?

My thoughts on this are a fractured or cold solder joint. It's clearly not the mechanicals.

What is the panel device at your desk at 2:02? Wire, Shot, Dave, Tagano, B-Cam, PC.... An audio mixing device?

I was checking my calendar, is it April 1 already?

My money is on a cracked capacitor or trace, you noted the board sprong up when the screws were released and it is possible that putting that much prssure on the switch cracked one on the other board.

Those vias on the tracks seem to have rather small gaps

hi, you should not have BM235 / 121GW Case anymore, I have not seen it in a long time

I have the same issue on my el cheapo meter, also same on Ohm range, same angle too @_@

I suspect excess Chinesium on the switch contacts. Chinesium is colorless and odorless. Dampen a rag with some aircraft-grade skookum and gently wipe the contacts and the switch wipesr.

Nice watch By the way

is it something odd, that 1 or more buttons end up being pressed as you wiggling the switch?

Look with sharp eye over the 10 slider contacts in a row to see if one is laying low. Press them on a flat surface to convince yourself that they positively press on the PCB. Also try if the angle of the knob a few degrees to left or right makes the fault differ. But first I would try to make the meter work out of the casing, to see it work without the knob. This because the nodge mechanism is in the top knob ? So tolerances of the hexagon shaft plays a part too ? I have the 325, and to a friend I vented last week that the only thing I don't like about the Brymen is the switch feel; it is raw, and with my large hands I need a lot of fingers and force to make it rotate. As if the design lacks behind the rest, specially when I compare with e.g. my Philips PM2403 from the 1960's, with a 16 position switch.

Oh god I just ordered one last night from eevblog...Am I going to be OK Dave?

A stress fracture on the PCB???

And it is brand new dmm So ? what is the price of it again ❗😉

... that’s what she said! 🤘

You were really yanking on it. I think the one is just a little loose and the other one you are pulling on it hard enough to pull the contacts apart.

i was gonna suggest a dirty track..some oil or something on it... but then ya swapped them over and it did it on both!...thats a serious WTF one! maybe over time the plastic is rubbing somewhere and slightly changing the tolerances...

My BM786 seems fine :D

My BM257s doesn't measure resistance anymore. No clue why. Doesn't seem like a switch or solder joint issue.

Were do i buy EEV bog multimeter?

Can you recommend any reputable dealer where I can purchase APPA Technology products? I'm looking for a way to purchase the APPA 172 meter. Any help would be appreciated. Thank you.

At 7:54 is that a deep scratch or crack across the second trace up from the bottom trace in the 7 o'clock position

could it be the battery contact!!!

When you screw into plastic, why don't you try to move screw backwards to find the thread it already made in the plastic? If you are making a new thread every time it will fell apart after like third disassembly.

Melted hole in dial pad at 5 o'clock direction from center

It is necessary to stay away from newly manufactured devices for a while. I think this prediction turned out to be correct. The brymen 869s have proven themselves. It would be sufficient to upgrade rather than produce a new one.

My bm786 is fine. I like that problems are being investigated.

Got exactly the same problem on my new BM786. But I've having it on ALL the positions. Worst at the top(from mV to Temp) :-( Update: The top right screw of the switch was very loose. After tightening this the problem "only" exists from DC V to the Temp option. But still only a slight press from the top(lcd side) and down (to the connectors) and it reboots every time. I am not able to get it to power of permanently as before.

"Countless hours"; story of my life.

I’m not happy with the LCD contrast on mine. Would you be willing to share the component designator for the contrast resistor in the BM786 so I can tweak mine?

not enough spring pressure

Dave, which meter is good the 121GW, BM786, or the BM235? I've always had flukes at work when I was working in Engineering, but I am retired now and I do not have a good one anymore. all mine had gotten too old (from the 1980s) and have died. money has been tight but I am getting my Stumilus $$ and all the ones I have now are POS and not that great. I am in the USA. is the 121GW going to be back in stock??? thanks

Don't complain about this, it's still not a mature product, so the customers are still testing it by using it daily. At the same price fluke offers us the 110 model (search it on tme) which only has voltage, resistance and continuity but it is a mature product that maybe does not have glitches like this anymore.

Again, tight as _ _ _ _ . Maybe the screw too tight and the PCB under a pulling stress, causing bad contact of components.

Who was thé winner of thé oscilloscope ?

broken run, crack in the pcb or component from stress?

These multi positional switches are so inconvenient on such a light devices. It is hard to turn them with one hand and most of the functions are selected with additional button presses anyway. It is time to stop listen to people who have fetish on those switches and are just like to "wiggle wiggle yeah" and move on to a better user interface.

Got to be a crack in one of the tracks

Cold solder joint somewhere…

Having the main board thicker would be better IMO. The board in the DMM appears to be no thicker than the board in my PC wireless mouse, Logitech Pro/M70. Obviously the mouse is much smaller than the DMM. I think the board in my Fluke 8060A handheld DMM is thicker then the BM786.

"Tight as a nuns nasty" is an Australian engineering term.

So have multimeter without rotary switches. Less mechanics to go wrong. OR Increase cost to improve mechanical robust solutions?

Pressure on pcb causing bad solder joint to reset meter? does not explain the nose and movment though. Intermitent faults are such a pain 😂

Damn Heisenbugs

1:43 - Who on earth leaves screen protector film on?_

22:09 add it to your soundtrack :D

Maybe it would better if these knobs just had one big switch per position and then relays could do whatever the switch used to do...

me texting her how good im gonna handle her needs me there @3:03 being told to show her already what these hands do

Do you assemble them locally or from china?

Uncle Lao came a gutsa