We do want to help. Having re-read this thread, I still don't know how often the trip happens - if at all. At some stage you'll have to do something that can't be undone.
- It could be speaking to some of those who were involved in the design of the microcontroller board. I was never brave enough to do that kind of thing when I worked in a large company. But those who were ended up extremely successful and useful employees.
- Or it could be cutting the wire that runs from the power-supply to the microcontroller board, inserting a 1 Ohm resistor and using an oscilloscope to track the voltage on either side of the resistor. This could sort-of be undone by replacing the wire once you've gathered all the useful information. People will see your soldered joints.
- You could temporarily tack a wire from the reset pin on the microcontroller to Vss, assuming that's not directly tied to a different power-rail. If that's brought out anywhere convenient. If in doubt use a (say) 100 ohm resistor. Even after you remove the wire it won't look pristine. And then the microcontroller will permanently be held in reset, so all you see is what happens before the microcontroller comes up. And it's up to you to determine if that's any better or worse as regards the power-supply tripping. Once you remove this wire there will be some evidence of "history" on the pcb. Take photos with your phone and make notes of what you're trying and what effect it has. The designer of the pcb should be helpful as to a good place to attack.
I'll say I don't have a current probe. I always regarded them as too expensive given how infrequently I would use them, and the different insight from the voltages either side of a series-resistor can sometimes be helpful.
