Frequently asked questions are about powering an APM2.5 or why the same does not work or why it has failed.
Here is a simplified schematic showing the major components of the 5V/Vcc circuit on the APM2.5
Target Audience: Readers who do not have Eagle or are confused about using it.
You Need: Basic electronic schematic reading ability
Note that I have separated the PWM Output section into the upper left corner with a heavy purple line that is bridged by the jumper JP1 on the APM2.5. This is to emphasize that diode D1 passes current through JP1 (and drops voltage). The remaining energy is then called 'Vcc'. Everything outside the purple corner is Vcc.
This is why the USB will power the APM2.5 when connected to a computer/USB hub. Note the fuse on the APM2.5 side of the USB connector AND another fuse on the output of D1. Another change from APM2.0 is the D4 6.0V Zener diode. If an over voltage is applied to the board, D4 will crowbar what it can to protect devices.
As with APM2.0, any 5V source connected to any of the indicated Vcc/5V points outside the purple corner (with GND of course) will power the APM2.5.
Also of note is the 'Mystery Port'. This port takes 5VDC before D1 and the fuse and is called 'JP_VCC'. Other clues to the mystery are the lines to 'ADC 12' and 'ADC 13'. A mystery indeed!
Any errors in this drawing from editing are mine.
I hope this can be used as reference for solving problems.
I don't think the difference in D4 will be a problem.
The purpose of D4 is to limit the Vcc value as a safety feature, not a supply regulator.
As you have seen, even a 6V zener is not sufficient to prevent overvoltage damage when connected too long.
In fact, if you were careful, you could operate without it -- as long as you were certain you have good power that does not exceed specification.
Tested today in-flight, everything was perfect, even dare to try arduplane for the first time (I am mostly involved with multirotors), and epic APM2.5 was in the air again :), after almost 30min of flight, landed safely.
It is wonderful to see someone apply troubleshooting methods, repairs techniques, and simple determination to see a problem resolved.
Well done! Thank you for the news!
Nathaniel Caner from the DevTeam Arduplane detected low voltage range for apm2.5. As he said, 4.4-4.6v has been seen from the logs. Might it be to Zener D4 (I put 6.2, instead 6v0)? Or something other is problematic? Brownouts has not occured so far...
D4 *should* only function when the rated voltage is met/exceeded. Unless the device is defective (it does not seem likely) the log value noticed is probably not due to D4.
There is no Vcc regulation on the APM. APM depends on external regulation with the Power Module, BEC, or ESC/BEC.
If the log value is legitimate, you may have moments of high current draw (from some device) that cause the Vcc regulation circuitry (again not on the APM) to dip.
seems that the problems are coming from the esc, since it is directly connected. PM or ubec might be the solution.