SCSI Termination, Unit Attention, Parity...

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robegian's picture
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SCSI Termination, Unit Attention, Parity...

Hi all,

I'm positive that the terms in the topic's subject deeply resonate in the memory of many of us, and I'm also pretty sure SCSI, as an acronym, in some time of its (definitely too long) life has spoken the line "I AM YOUR FATHER" to the FUD acronym. Anyway, I'm stuck in the following situation.

Tampering with my Power Mac 9600 in order to silence it, I've removed one of the two SCSI drives residing in the case, leaving just one active — which has always been the actual boot disk (the other was just for data). This is the device at the end of the SCSI chain, thus with SCSI Termination ON, and Termination Power ON. The problem is, the Power Mac doesn't boot anymore, and the display stays black. The drive spins but nothing happens. The same drive worked flawlessly before I removed the other drive.

I tried disabling Termination Power, leaving SCSI Termination ON: it does'nt work. Then I tried disabling SCSI Termination: of course it does'nt work. I'm still unsure if Termination Power has to be ON (although it was ON when the thing was working along with the other disk).

Then my attention went to some other jumpers: Unit Attention, and Parity. I seem to remember that in Power Macs, Unit Attention and Parity must be enabled: am I wrong? And by the way, what about Auto Spin and the other parameters?

In one question: what is the right configuration of a SCSI drive in a Power Mac?

A bunch of pics depicting the situation: the Power Mac 9600's SCSI bus (I removed the SCSI 1 device); the jumper setting of the SCSI 0 device (the Power Termination ON/OFF jumper is located in another area); the exotic jumpers of the SCSI 1 device — by the way, no termination jumper?

eeun's picture
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Joined: Dec 19 2003 - 17:34
Re: SCSI Termination, Unit Attention, Parity...

A black screen sounds more like there's a hardware problem elsewhere. No visible boot drives should still boot to the grey question mark screen.

My 8600 died with the same black screen symptom (aka no video), and I've yet to get it working again. It's been a while so I can't remember whether or not I had a startup chime.

robegian's picture
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Joined: Nov 14 2005 - 04:22
Re: SCSI Termination, Unit Attention, Parity...

Thanks for the reply.

In the meantime, I tried pressing the CUDA switch, which allowed a tiny step forward: now the display lits, and the smiling Mac shows. The problem is that it smiles forever, as if the Mac froze at this stage.

Anyway, even if it won't help my particular situation, it would be useful to get some information about Termination Power, Unit Attention, Parity and the likes.

P.S. The startup chime has always played.

robegian's picture
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Joined: Nov 14 2005 - 04:22
Re: SCSI Termination, Unit Attention, Parity...

... and after quite a bit of search in the net, I found that I have to set:

• Termination ON

• Termination Power OFF

• Unit Attention Disabled

• Parity Check Disabled

• TI Sync Negotiation Enabled

Now the system seems to work properly.

eeun's picture
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Joined: Dec 19 2003 - 17:34
Re: SCSI Termination, Unit Attention, Parity...

Thanks for posting what finally worked. It's a great reference.

I'm amazed that scsi problems could cause a black screen, but scsi has always been a tempermental and mysterious interface. The "scsi voodoo" term is well-earned.

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