| Products > Test Equipment |
| BM786 Switch Issue |
| << < (11/15) > >> |
| EEVblog:
--- Quote from: Fungus on March 29, 2021, 07:52:05 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. --- End quote --- 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. |
| joeqsmith:
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. |
| bdunham7:
--- Quote from: joeqsmith on March 29, 2021, 01:00:56 pm ---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. --- End quote --- 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... |
| dcac:
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. |
| EEVblog:
--- Quote from: dcac 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. --- End quote --- I did, and there is no evidence of any damage. |
| Navigation |
| Message Index |
| Next page |
| Previous page |