OK, well, I had to look another PTW that had failed on the weekend. The owner reported smoke coming out of the buffer tube. I did a complete teardown looking for burnt electronics, but found none:
This black spot on the ECU looked like a promising candidate, but it turned out to be a spot of crud.
Water did enter this gun. You can see residue on the selector board and the right side of the gearbox. The gun still ran during the RAAT downpour, but it went 3-burst in both modes.
The FET board looked fine, no obvious signs of smoke release, for that is the magic that makes electronics work. Once you let it out, things stop working.
That lead me to the final culprit, and here it is:
The motor was caked in burnt brush dust:
Now, there is always some amount of brush dust present on a motor. If it is shiny and copper-coloured, it is a sign of brush wear, sometimes premature due to a commutator that is not true. But this dust is black. That means that it has been burnt. The mechanism of this burning is the arc formed between the brush and the commutator. It can happen for alot of reasons. One of them being a damaged brush. It could also be a poor commutator, broken brush spring, poorly moving brush, weak brush spring allowing the brush to skip on the commutator.
At any rate, this motor is likely toast. It has seen perhaps 25,000 rounds, maybe a bit more or a bit less. I will look into it further once the owner and I have spoken.
Now, it would be a little unfair to readers of the previous posts on the 416 gearbox failure if I did not provide a frame of reference for the issues of lubrication, gear lash and wear. So, with this gun, a 2012 Systema, I figured I would tear it open to show you the differences. I already knew it as soon as I openned the 416's gearbox, but just to give you a comparison:
FCC:
Systema:
FCC:
Systema:
Please note the gear lash and lubrication. I relubed the Systema box this spring, and I do it the same way Systema does, grease in the right areas and no more than necessary, the gearbox must have lubrication, but it should not be dripping grease everywhere. Some is better than none, and too much is worse than none.
The more I look at FCC, the more I want Systema.