Hello, I am attempting to recover data from several MFM/RLL disks given to me by a friend of the family, including controllers. Of course, the first two drives went well, but the third one is killing me.

Controller: DTC 5150XL
Mechanism: Shugart 712

The disk spins up, positions to track 0 and asserts it's READY signal. However, during boot, either nothing will happen and the system hangs indefinitely, or I get a 1701 disk error and the system hangs indefinitely.
Either way, if the disk is attached, the system hangs and does not proceed to boot. I have noticed, if I leave the control cable disconnected during boot, the system BIOS reports "Primary master hard disk fail" and I can press F1 to continue to boot. If I connect the drive at the DOS prompt, the system continues to be stable and responsive, though 90% of software reports "No hard disk."

However, I have found software such as HDAT.COM which irregardless of this can request the drive to seek. The heads move and everything sounds fine. It does list several hard sector errors in cylinder 0 and cylinder 1. I believe that this is what's causing the system to hang. Unfortunately, I'm not aware of any way to "fix" this problem, so I have another idea instead.

Obviously, the drive is capable of moving and successfully reading data. It passes a seek test no problem and one benchmark program actually gave me some average seek times. The disk works!
But the machine will not boot with it connected and I am not sure why. However, I can get the machine to boot just fine with it disconnected and just hitch it up afterwards.
This second solution seems to "work," but I am left with the problem that the BIOS reports NO disk present.

Is there a way to "spoof" the BIOS in DOS and make it appear as though there IS a disk after a "Hard disk fail" error? Or, is there a way to stop the machine from hanging?

For the record, I thought about just putting this to the side and moving to the next drive+controller, but that Tandon TM-252 is putting up one heck of a fight so far. I figure the Shugart is a better bet because it is mechanically working.

Any suggestions are appreciated. I have other controllers if you think it might help. I seem to remember a "CMOS Spoof" setup that was possible, hence why I ask.