Products > Test Equipment

BM786 Switch Issue

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EEVblog:

--- Quote from: joeqsmith on March 27, 2021, 06:28:02 pm ---
--- Quote from: Algoma on March 27, 2021, 05:54:16 pm ---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:

...

Highest 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 electrician

The 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.

--- End quote ---

As 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.     

--- End quote ---

Joe, 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.

joeqsmith:

--- Quote from: EEVblog on March 28, 2021, 10:28:02 am ---Joe, 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.

--- End quote ---

Because 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/#msg3516068
https://www.eevblog.com/forum/testgear/bm786-switch-issue/msg3532326/#msg3532326

bdunham7:

--- Quote from: EEVblog on March 28, 2021, 10:28:02 am ---This is a factory fault.

--- End quote ---

That 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.

floobydust:
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.

EEVblog:

--- Quote from: bdunham7 on March 28, 2021, 04:39:27 pm ---
--- Quote from: EEVblog on March 28, 2021, 10:28:02 am ---This is a factory fault.

--- End quote ---

That 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. 

--- End quote ---

As 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.

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