fretting shorting out card edge connectors?

[coppercone2]

I had to replace the kelvin probe cable on my DE5000 meter. Seemingly it passed calibration but it was giving me bogus readings on stuff with the kelvin input thing.

I opened it up and inspected it and it looked fine, then I decided to look for a short. Basically all 5 pins were a dead short to each other (like 0.25 ohms), measured from the alligator clip to the solder joints on the PCB. I did a full inspection of the cable shields before putting it together, being sure to trim every single wire and heat shrink cover the shield and do a magnified inspection of the cable, because sometimes you get trouble from a cable shield.

I cleaned the flux after I soldered the wire, and I cleaned the board again when I was trouble shooting it, and I don't see anything change, its still reading shorts. WTF

I looked carefully at the blades, and there was a fair amount of dark discoloration on the edge of the PCB where it inserts into the spring leaf receptacle . I scrubbed this down with acetone and it suddenly starts to read in the mega ohms, now its gonna get ultrasonic cleaned after I sand it down.

The best I can figure, is that repeated insertions lead to scraping of the circuit board and the connector, that built up on the edge, and shorted everything out.

It was driving me nuts because the PCB itself is like pristine lol.

The rough surface between the circuit board... seems to accumulate crap.

Has anyone seen this with card edge connectors before? I never liked right angle PCB's. I feel that it needs to have a smooth polished surface there, not abrasive that builds up metal. It seems there should be a proper card edge connector, the hack of using the PCB as a connector is vulnerable to this! it was making me question the laws of physics (I began to wonder about some kind of crazy dendrites, or conductive transparent films, etc)! This failure mode makes this style of connector feel mega bootleg.


You know what, I just bought a new one. I was going to do something but not for what its worth lol. I am not gonna sand god damn fiber glass