Measure the voltage on pin 25 relative to the ground shell of the SCSI DB-25 on the lower rear back center. Expect about +4.2V. If not check L10 L9 L8 D3 F3, they are on the DC path to power the SCSI controller chip UI12 and SCSI terminator power you just measured. If fuse F3 is blown, replace with 1A unit. D3, 1N4001. Open chokes may be temporarily jumpered for test purposes.