I need help figuring out what fried on my APM 2.6. It turns out the 3DR power module that I was connecting my board to is putting out waaay more than the 5V to the board...so naturally...my board was toasted cause I didn't check the 5V before hooking it up!! We all know what "assume" stands for.... :/
Anyway, I replaced the power module and checked my voltage regulator and the output is 3.3V with a 4-5V input. After spending some time searching online, I'm unable to come up with what may be dead on it. All the fuses I can find (the ones by the PM cable and the micro USB connection) are fine.
For clarification, have not been using JP1, only was powering through battery (XT-60 connectors), or USB (always seperately, never USB and battery at the same time).
I've downloaded the schematic and opened it using Eagle. F2 and F1 have continuity with an ohm meter. It looks like the protection circuit didn't work? I imagine since F2 isn't blown, then any number of chips could be fried. Considering the LED's A and C are flickering on and off then most of the board must have been exposed to the overvoltage?
The USB won't recognize at all...I imagine the MEGA32U2 chip is dead...tried reflashing it...computer couldn't see the chip.
Sounds like you have covered more than 90% of my ideas.
The zener, D4 can only do so much before it either blows or shorts out. D1 is for reverse supply connection protection but as you were using a PM, that should not have failed. D1would fail with either high reverse bias voltage or forward bias overcurrent.
With 5V (or slightly more) out of the PM and 3.3V regulated, you are correct to be concerned about other components.
I have never had an APM get to that state, yet.
Because you attempted a reflash with no obvious success, it looks like your options are running out.
How old was the PM and have you contacted 3DR about the failure? I am guessing you purchased them together.
On the other hand, if you purchased another brand, it would be quicker to purchase another and then use a running unit for comparison troubleshooting -- unless you happen to have another already.
It would be great if there were some diagnostic firmware we could load. Along with a break-out box, we could home in on an issue very quickly.
The PM that I was using that fried it was a 3DR PM that was about a year old. When I tested it was putting out about 10 V but by that time it was too late. I replaced it and am getting the correct PM 5V output but the APM is dead.
I contacted 3DR tech support and they got back to me much faster than I expected. They're replacing the unit :). It was a good learning experience though on APM hardware :).