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KyranF
KyranF
6:56 AM
I have encountered an issue where a logic chip on my board has died, and it dies in a way which shorts the logic supply of that chip to ground, but it's a weak short (or the regulator handles it well) and only pulls it down to 2.5 or 3v (from a 5V logical supply).

I had to go around my board and de-solder every IC on the 5V supply one at a time and power up and test to see which one was actually causing the short. after the 10 chips were each soldered and tested, the final one being the microcontroller in a super annoying 28-DIP package, ended up being the culprit. It wasn't obvious enough…
 
 
8 hours later…
W5VO
W5VO
2:38 PM
@KyranF Thermal camera, and maybe figuring out why the part died in the first place.
 
 
3 hours later…
octopus
octopus
6:00 PM
Hello, I was wondering if someone could help me with this:
What's the phase angle of the inductive reactance in a parallel rl circuit?
 
 
2 hours later…
KyranF
KyranF
8:10 PM
@W5VO I know of the thermal camera option - and as to why the part died, I know the general failure was the user (not me) being very poor with wire conductor hygiene and all sorts of sparks and ESD and silly nonsense was happening to the board. I'm surprised it even lasted as long as it did. This guy has it dangling by wires outside of a control box on the machine (it's an all-electric mobile farm utility tractor thing)
 
KyranF
KyranF
8:25 PM
but what about techniques like sizing a branch off the 5V supply where you know the operating current of an IC is maybe only 20mA DC, having a resistor (like 22 or 33 ohms) and then the local supply capacitors for each IC? normally I just have a flat 5V logic supply to everything, but branching it like that might be useful for diagnosing issues?
 

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