I bought a problem F90BT on EBay, and for awhile I figured I had made a mistake. Even though I followed the reset-eject-menu-map sequence perfectly, the unit would reboot about ten seconds later.

 

I was troubleshooting the unit on the bench, and the beefiest 12v supply I had sitting around was only 800ma, but I figured I wasn't playing music and it seemed to work. Well, I suddenly remembered I had an old transformer battery charger in the garage that ouputs up to 10A, and once I hooked that up, all my problems went away, and I was able to recover the unit.

 

So, if you are having reboot problems, be sure your wiring and power source are capable of supplying enough power.

 

Also, don't forget to ground the parking switch during testing.