Author Topic: BM786 Switch Issue  (Read 11861 times)

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Online EEVblogTopic starter

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Re: BM786 Switch Issue
« Reply #50 on: March 29, 2021, 09:41:13 pm »
Maybe 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.

I'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.
 
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Offline joeqsmith

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Re: BM786 Switch Issue
« Reply #51 on: March 30, 2021, 12:13:24 pm »
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.
 
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Offline bdunham7

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Re: BM786 Switch Issue
« Reply #52 on: March 31, 2021, 05:42:43 am »
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.

OK, 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...





« Last Edit: March 31, 2021, 05:53:41 am by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline dcac

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Re: BM786 Switch Issue
« Reply #53 on: March 31, 2021, 10:33:29 am »
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.

 

Online EEVblogTopic starter

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Re: BM786 Switch Issue
« Reply #54 on: April 11, 2021, 05:25:38 am »
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.

I did, and there is no evidence of any damage.
 

Offline HAO

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Re: BM786 Switch Issue
« Reply #55 on: April 10, 2023, 04:05:29 am »
I have the same problem with my Brymen BM789. Does anyone know how to fix it ? :palm:

« Last Edit: April 10, 2023, 04:07:45 am by HAO »
 

Online J-R

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Re: BM786 Switch Issue
« Reply #56 on: April 10, 2023, 08:58:51 am »
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?
 
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Offline HAO

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Re: BM786 Switch Issue
« Reply #57 on: April 10, 2023, 04:01:04 pm »
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?
Here is my issue :
https://m.youtube.com/shorts/QUmqFHYuMGI
 

Offline Pokey44

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Re: BM786 Switch Issue
« Reply #58 on: April 12, 2023, 07:22:05 am »
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!
 

Online J-R

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Re: BM786 Switch Issue
« Reply #59 on: April 12, 2023, 09:30:02 am »
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.
 
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Offline Pokey44

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Re: BM786 Switch Issue
« Reply #60 on: April 14, 2023, 02:41:55 am »
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.
 

Online J-R

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Re: BM786 Switch Issue
« Reply #61 on: April 14, 2023, 04:00:18 am »
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?
 

Offline Pokey44

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Re: BM786 Switch Issue
« Reply #62 on: April 18, 2023, 10:37:43 pm »
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?
 

Offline mwb1100

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Re: BM786 Switch Issue
« Reply #63 on: April 19, 2023, 06:41:10 am »
it's been too long (ordered in October 2022), and follow-up questions for support/warranty went unanswered

From the last page of the manual:
Quote
To obtain warranty service, contact your nearest BRYMEN authorized agent or send
the product, with proof of purchase and description of the difficulty, postage and
insurance prepaid, to BRYMEN TECHNOLOGY CORPORATION.

Contact info is:

BRYMEN TECHNOLOGY CORPORATION
TEL:+886 2 2226 3396
FAX:+886 2 2225 0025
http://www.brymen.com
info@brymen.com

If you seek warranty assistance directly from Brymen, let us know how it goes.
 
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Online NoisyBoy

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Re: BM786 Switch Issue
« Reply #64 on: April 19, 2023, 06:38:30 pm »
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.
« Last Edit: April 19, 2023, 06:42:13 pm by NoisyBoy »
 
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Offline Pokey44

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Re: BM786 Switch Issue
« Reply #65 on: April 21, 2023, 12:41:17 am »
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.
« Last Edit: April 21, 2023, 12:44:33 am by Pokey44 »
 

Online EEVblogTopic starter

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Re: BM786 Switch Issue
« Reply #66 on: April 21, 2023, 01:14:05 am »
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.

If you purchase an EEVblog branded Brymen then I handle the warranty exchange from my own stock. Every other dealer should do the same.
 

Offline floobydust

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Re: BM786 Switch Issue
« Reply #67 on: April 21, 2023, 02:51:48 am »
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 mosfet  :-//
I couldn't make out the SMD marking codes for them in Dave's video EEVblog 1520 - Troubleshooting a Faulty BM786 Multimeter but it's worth a check in the case the rotary switch is not the problem, it's just weak power causing erratic behaviour.
 

Online NoisyBoy

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Re: BM786 Switch Issue
« Reply #68 on: April 21, 2023, 08:52:45 pm »
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.


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.
 

Offline Hydrawerk

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Re: BM786 Switch Issue
« Reply #69 on: April 23, 2023, 08:59:45 pm »
How common are switch (or other) issues on BM789 / BM786? I might want to buy one in future...
Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 

Offline giosif

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Re: BM786 Switch Issue
« Reply #70 on: April 23, 2023, 09:19:56 pm »
[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).
 

Offline Pokey44

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Re: BM786 Switch Issue
« Reply #71 on: April 27, 2023, 12:11:01 am »
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.

If you purchase an EEVblog branded Brymen then I handle the warranty exchange from my own stock. Every other dealer should do the same.

Thanks 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.
 

Online EEVblogTopic starter

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Re: BM786 Switch Issue
« Reply #72 on: April 27, 2023, 01:01:57 am »
Thanks 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.

That 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 Returns
PO Box 7949
Norwest NSW 2153
AUSTRALIA

I'd like to look at what the issue is. Please include your details.
 
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Offline Pokey44

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Re: BM786 Switch Issue
« Reply #73 on: April 27, 2023, 05:38:00 am »
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.
 


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