If swapping the coin door pcb doesn't work, I guess you can isolate the coin door / coin door pcb assembly if you remove the corresponding connector from the CPU board and play. If the problem reoccurs then it may be an issue on the CPU. On my HS2 I had issues were it was going straight into the test menu from boot (as if the button was held down)...However this was due to acid damage.
Could still be a problem at the CPU, but always easier to start with the basics, isolate as Marty has suggested.
