Hello ,
If the Machine Doesn't boot from Hard Drive it might be because of thr A2000 Motherboard Revision.
CBM Service Bullitin # C3-1.14 (May 20,1989)
A Problemn has been found with the A2620 Accelerator and A2090 Hard Disk Controller with A2000 Motherboard revisions 4.1, 4.2, 4.3 or 4.4.
This is seen as read/write disk errors or memory failures with this configuration of hardware.
The problem may be solved by adding a pull-up resistor on the _BAS signal.
The rework is to add a 3.3K ohm resistor between pin 20 and pin 11 on U605 (74LS245). This chip is located near connectors CN 600 (86 Pin expansion slot).
Cheers
Shaf