See if this could be of help to you;
Telemetry data out from the APM is not straight forward, Telemetry is only using UART0 wether the APM is airborne or it is connected to PC via USB. The only difference is that while APM is connected to PC, ATMega2560 reconfigure UART0 to baud 115200 bps else when the APM is airborne it configures the same UART0 to the baudrate selected by the user for telemetry, default is 57600 bps, I am trying to explain;
STATE WHEN APM CONNECTED TO PC VIA USB (STATE-1):
When APM is connected to the PC via USB then this state is sensed by (Failsafe & USB controller) chip ATMega32U2, which in turn makes its pin #5 high which is connected to the control input pins #1 (IN1) & pin #5 (IN2) of the chip TS5A23157 (ACTIVE) Dual 10-Ohm SPDT Analog Switch.
This state is also communicated to ATMega2560, which reconfigures the UART0 to baud 115200 bps by default. In this state the chip TS5A23157 (SPDT Analog Switch) connects UART0 of ATMega2560 (Pin #2, #3) to the UART1 of ATMega32U2 (Pin #8, #9). The code running inside ATMega32U2 directs the USB to serial connectivity to ATMega2560's UART0. In this state, TX & RX signals of the Telemetry radio, on the regular port are disconnected from ATMega2560's UART0.
In the above screenshot of the Schematic and following PCB screenshot, just focus on the highlighted connections.
STATE WHEN APM IS AIRBORNE (STATE-2):
When APM is powered via ESC or power module the this state is also sensed by ATMega32U2 which makes it pin #5 low which is connected to the control input pins #1 (IN1) & pin #5 (IN2) of the chip TS5A23157 (ACTIVE) Dual 10-Ohm SPDT Analog Switch.
This state is also communicated to ATMega2560, which reconfigures the UART0 to user selected baud 57600bps by default.
In this state the chip TS5A23157 connects UART0 of ATMega2560 (Pin #2, #3) to the telemetry radio.
In the following Schematic and PCB screenshot, just focus on the highlighted connections.
Your screenshots didn't make it for some reason.
My problem is that I am trying to figure out why I don't have Telemetry on the 3DR port when powered by the power module. It isn't a radio configuration issue as I have actually had them talking to each other when the radio one is connected by the FTDI cable. I also have solid green lights but no data flowing.
Baud rate and port numbers are correct. I don't see this as a software issue, but a hardware failure issue and I was hoping to work around it. I got this board in the fall, but I am only starting to put it in play.
However I do not have much knowledge about it but could you see if the data flow is okay when you use the through holes pads as used by him in the following image which he basically used for frsky telemetry to mavlink conversion.
"For example I am running dual telemetry from APM2.52, one is the regular telemetry to mission planner in PC and other is to the Transis X9D's display screen via X8R Receiver & Teensy 3.1. There is separate blog by Rolf."
Thanks, that is helpful. Too bad the Eagle files are not available so I can understand some of the layers better.
Sadly, unless I can fix this issue, the board is of no use to me if I can't communicated with it via RF.
I really appreciate your help so far.
Check link at bottom of page http://store.3drobotics.com/products/apm-2-6-kit-1
Eagle files Open-Source-Hardware
Eagle Freeware download:
Thanks for all the help. I learned a few things today.
Once I have replaced it tomorrow, I will let everyone know if my final guess was correct.
Thanks... I see that.
The data still has to go through TS5A23157, and that is where I think my problem is. It isn't switching from the data to travel through the telemetry port while the USB connection works fine. SJ1 and SJ4 are hardwired to MUX TX and MUX RX and that goes into pins 9 & 7 of the TS5A23157. I should really scope Pins 1 and 5 and see if their logic is changing when in flight mode.
I am still hoping that 3DR will honour the warranty on this unit. I was reviewing their Terms and it isn't very clear how long the warranty is on these boards from them.
For anyone elses notes, Pins 1 and 5 are 0V for the Radio port and 5V when USB is connected. I confirmed that those levels are correct for my board and yet the data from the radio isn't making it on Radio.
Pin 1&5 of the TS5A23157 are connected together to pin 5 of ATMega32U2. So you should see if the logic level is changing between low and high while changing APM power from USB to battery
So basically what I learnt recently that pin 5 of ATMega32U2 decides the state of the analog switch TS5A23157.