The 74LS259 still hasn't arrived, however, while waiting, is there anything else that should happen during the normal TI startup sequence that I should check for on the card, in order to determine if there are other faults elsewhere, since even when the drive is selected properly it refuses to work?
There is a little trick that I know, that doesn't actually do anything else then make sure that the FDC card is "connected" to the drives...that is , to take the "card edge " connector, and, turn it upside down...purposely. If, when you do so, the drive(s) lights (LEDs) turn on AND stay on, ...that way, you know that the drives are getting SOMETHING from the card. Of course, when you've turn on the P-box to get the drives "lit" , make sure that you turn the power off (to P-box, and, drives that are being powered w/o the P-box Power Supply)....and then switch back the "card edge" connector the right way again.
I hope this helps....
Having VERY similiar problems with my CorComp FDC.