This thread is getting old, but I may have a similar problem. I was lucky enough to pick one up, played at sellers, then brought it home. Put it together and everything looks good except I get that "coin door open" message. I did find one of the leads to the back side of the door close switch (beneath the 9 pin serial plug) had worked itself loose, but when placed back on, and attempted again, I still get the "coin door open" message.
I had to leave the very next day, so I haven't had time to do a proper check of all possible fault areas, but I am curious if you were finally able to solve your issue?