Defective Power Module?


I recently purchased a second hand Hexa B with a APM 2.5 and a new in package 3DRobotics Power module that was never installed by the former owner. I have successfully rebuilt the machine as well as flashed the APM with AC 3.0.1. I installed the 3DR Power Module according to the online guide as well as removed the J1 jumper.

Problem: The flight data and battery monitor both read 0 volts. (See attached screen shots) and the APM will NOT power up the Spektrum AR8000 Rx. I tested a second Rx with no success. However, via the CLI I can successfully test the 6 motors.

My two current working theories are 1) The red and black power cable from the APM to the Rx is defective and needs to be replaced. (already on order). Or, 2) the “new” power module is defective.

I have test 3 separate batteries with this system. A 5200mah 3S and 2 x 4S 6000mah. All 3 show 0 volts BUT do display AMP’s etc.

Any thoughts or ideas?

Thank you in advance,


How are you communicating with the APM when you are powering it with the PM. Telemetry I assume as you should not have the APM powered by the PM and the USB at the same time.

Have you followed the instructions in the wiki to enable the voltag/current measuring function:
Additionally, I believe that you need to define the APM analog pins in the MP Advanced Parameter List that will be used to measure the voltage and current coming from the PM.
TCIII ArduRover2 Developer


Thanks for the response. I did indeed follow the wiki link … -with-apm/ However, I did not use the power analyzer described in Randy’s video.

Hmm… I was connected to the APM via USB to MP AND connected to the flight battery via PM at the same time. I will try it again.

I did not see any mention of the analog pins being used on the APM? Can you point it out?

The Power Module has a single 6 pin connection to the APM which is located directly next to the spot for jumper J1 which has been removed. It is also labeled “PM”. Other than that, I have only the GPS, input and output signals (1-6) and power connections that lead to the PCB (output side) and the Spektrum AR8000 Rx (input side).

As I mentioned, within the MP software, I do see battery metrics, just not volts. Volts = 0.

I am starting to wonder if the PM is fine and the real problem is the 2-pin power cable between the input side of the APM and the Rx is bad? I am glad I ordered 2 more just to be sure.



Is your APM a genuine 3DR product or a clone?
There was a change made to the speed of the SPI bus in the newer software that can show up an APM onboard voltage regulator defect in some genuine and clone APMs.