Products > Test Equipment
BM786 Switch Issue
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EEVblog:

--- Quote from: joeqsmith on March 28, 2021, 03:01:20 pm ---
--- 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.
--- End quote ---

No, it's you questining the owners account that I had a problem with.
joeqsmith:

--- Quote from: EEVblog on March 29, 2021, 01:15:35 am ---
--- Quote from: joeqsmith on March 28, 2021, 03:01:20 pm ---
--- 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.
--- End quote ---

No, it's you questining the owners account that I had a problem with.

--- End quote ---
As 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. 
bdunham7:

--- Quote from: EEVblog on March 29, 2021, 01:12:18 am ---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.

--- End quote ---

Maybe 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.
joeqsmith:
"... 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. 
Fungus:

--- Quote from: joeqsmith on March 29, 2021, 01:00:56 pm ---"... 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. 

--- End quote ---

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.
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