I've been getting the following error when trying to upload to my ArduPilot 328 using the FTDI cable
avrdude: stk500_getsync(): not in sync: resp=0x00
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51
This is on an ArduPilot that was working (able to add and retrieve way points) a few weeks ago. I'm now getting the same error with an older blue ArduPilot 168. The FTDI cable seems to work, as I'm able to upload sketches to an Arduino clone (also 168). I get the error on 2 different windows and 1 linux machine, with both Arduino IDE 16 and 17. I've tried with and without the shield and all the pins appear to be properly soldered, although I suppose I could go over them once more with the soldering iron.
Any idea on how to troubleshoot this problem? Are my ArduPilots fried? Any way to check? Should I get a new cable? Any suggestions would be greatly appreciated.