• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

SCSI HD only works with external terminator attached


Well-known member
Hello everyone

I have this 1050MB IBM 50 pin SCSI drive which came out of a Powermac 7500 and worked somewhat reliable on its internal SCSI bus. However, when I use the drive inside a Quadra 700 or Performa 475, it only spins up (!) if an external Terminator or another device with termination is attached.
The jumper for termination is set, so I have no idea where the issue is.

Any thoughts?


  • D792EB09-1BB4-4837-9B4F-CECEC2228E3B.jpeg
    3.3 MB · Views: 11
  • 3D76C882-57A7-49B2-83DF-FC5117A06E3E.jpeg
    4.3 MB · Views: 12


Well-known member
It appears to be missing the resistor packs (or equivalent) at U6 and U7.

Only some logic boards provide automatic termination and I don't think the 475 is one of them.

If you don't want an external terminator hanging off the rear of the machine, look for a 50 pin terminator.


Well-known member
It may be useless. I could see Apple shaving off some pennies by ordering a large run of drives like this.