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SCSI HD only works with external terminator attached

robin-fo

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?
 

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ymk

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.
 

ymk

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