RJ3ib wont start PSU fuse F3 keeps blowing

Hi,

I am a small manufacturer in Estonia, and I got good deal on used 2004 Fanuc m6-ib robot. Been using the robot for few months and currently I am building robotic grinding cell. I was connecting some inputs and suddenly I/O board 2A fuse blew. Its weird I dont know what I did wrong. When the I/O board fuse blew I was connecting some input wires that were not even being powered. At that point I could still move the robot and servo stuff seemed working.

Replaced the 2A fuse and disconnected all I/O devices. Upon start up the F3 7,5A fuse on PSU (24E circuit) blew. Robot starts and I get FSSP init error (fuse blown). I ordered more fuses and now robot wont start with the F3 fuse installed (red alarm LED on PSU). If I take the fuse out the robot start with error.

Maybe the the i/o board is internally shorted? (looked OK)

What else to check, PSU, servo amp or transformer?

Thanks for suggestions

OK I got the robot working.

Disconnected the servo amp cable and turned on the robot. Cycled e-stop and deadman switch.

Shut it down and then put the servo amp cable back and restarted the robot. Machine powered on and everything works like a miracle. Maybe the estop board had a sticky relay thats why it blew the fuse, i dont know. Anyway its fixed now.