This machine was donated to Kennett Classic as unoperational. I replaced the power supply with an original IBM XT supply and replaced the hard drive controller card with a similar clone card. I temporarily replaced the bad Mitsubishi disk drive so I could access the hard drive to revert the OS from IBM DOS 3.3 to MS DOS 3.1. Someone had attempted a disk doubler, but failed to get it working correctly. A THESYS RAM / serial card was installed, but I am unsure if this card was added later or came originally with the system. The diskette drive controller card is branded "PC'S LIMITED"
There is no known operations / hardware guide for this motherboard, but similar board's documentation is enough to assist with diagnosis of problems.
NEXT: System often boots up to an error message:
ARC Turbo Board
X Turbo System Error # 04
Sometimes the system boots without error, and additional system info is displayed to indicate turbo mode is active. One simply hits enter to bypass the message. System reports a full 640K RAM. I believe the Turbo mode is not active when the error appears, which I assume means the system operates at only 4.77 Mhz. So the next thing is to fix the Turbo issue.
Also - The display when first powered on displays in red, it will need service.