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Apple 40SC strange power supply...

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I have an old 40sc that I just finished refurbishing. It all works very well.


Here is the drive in my setup.




I retr0Brited the case, and changed out the hard drive. I replaced the old quantum Q250 with an IBM P-series 857mb.


The interesting thing, is that the power supply of the 40sc has permanently modified the hard drive. When I first got the IBM drive, I could plug it in to any standard power supply and it would fire up immediately. After I connected the hard disk to the power supply of the 40sc, it would no longer fire up at all. It wouldn't respond to any power supply. The drive acted dead. Then, I went ahead and connected the scsi cable and plugged it into my SE, and the drive will fire up only when the SE is on and the scsi cable is connected.


So... turn on the SC. nothing but the fan. Turn on the SE, the drive comes on. The scsi drive will still not work in any other power supply.


Everything works, and this isn't really an issue, but why has it happened?


Is this some type of power save activated by the power supply in the 40sc? Do any of the scsi experts know what this is.


BTW, tried two identical IBM drives, both of them did this.

Edited by Recaptcha

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It is controlled by a jumper on some drives. Yours seems to be one with such a jumper, set to auto spin up. Here from a roughly contemporary IBM drive manual:


Enable auto spin up (JP5) 

This jumper controls how the drive starts when power is applied. If the jumper is NOT installed then the drive will spin up automatically after power-on reset. 
If the jumper IS installed the drive will NOT spin up unless the host system issues a 'START UNIT' command to the file.

Edited by beachycove

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Interesting... I did place a jumper on the drive because it wouldn't startup at all without it. Maybe that jumper 5 is what I ended up activating.


Thanks for the info.

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