The USB cable I am using works fine with the Due.
Yes I am using the right board and port.
I tried Nick Gammon's programmer, using a programming cable (reset -> D10 on the running Due).
The first attempt it seemed to recognise the Mega, and I could even attempt to program it. However it failed verification completely, and then after that, I cannot even get it to "enter programming mode" in many attempts.
Atmega chip programmer.
Written by Nick Gammon.
Version 1.37
Compiled on Sep 29 2017 at 22:26:54 with Arduino IDE 10804.
Attempting to enter ICSP programming mode ......................................................
Failed to enter programming mode. Double-check wiring!
Type 'C' when ready to continue with another chip ...
Attempting to enter ICSP programming mode ......................................................
Failed to enter programming mode. Double-check wiring!
Type 'C' when ready to continue with another chip ...
When the Mega is plugged into ICSP it powers up with the ON and LED next to AREF permanently lit.
Looks like it is bricked, or was a brick when I bought it from ebay.
Does anyone know what kind of diagnosis I could do? I don't mind writing my own code to probe ICSP etc. Is it possible to make use of this board at all or will I just have to throw it away?