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Mac IIsi and SCSI termination power

ironborn65

ironborn65

6502
Hi mates,
I have a Mac IIsi, fully recapped that is working fine except that the termination Power does not work. I have to power the blueSCSI to start it up, BTW the blueSCSI works fine in my other Macs like se/30 LC LC III. It works without external Power supply if I plug it into the external connector.
Any idea where I should look in the board for the culpit?
 
Last edited:
My internal ZuluSCSI requires power with the IIsi, whereas it doesn't with my LC III, so I think it's a function of the IIsi...
 
I always consider running any SCSI device off termination power alone a modern blessing. I know it works in many/most cases, but if I install anything like a SCSI2SD internally in a machine I use the supplemental power whenever possible.
 
The IIsi is one of the few machines that does not supply termination power to the internal SCSI port at all.
 
I was about to ask about SCSI termination power. Cool that a topic opened up about this.

Short form:

Any good references out there on the web about SCSI termination? Any ideas how a logic board can permanently damage a SCSI HDD?

Long form:

I have a logic board that seems to fry SCSI HDDs. I can take a newly-found SCSI HDD and attach it to the internal SCSI port, boot the system from an external Zip drive, and initialize/format/test the new SCSI HDD using 7.5 Drive Setup. But once I disconnect the new HDD, no system can use the HDD again.

Once affected, an HDD spins up, spins for about two seconds, then spins down. FWB Toolkit reports that the drive responds (FWB and SCSIProbe can both access the manufacturer data page) but nothing can start the drive. FWB reports "Check Condition" errors on the damaged drives. Drive Setup does not count the drive as present (doesn't find it at all).

The logic board's internal HDD power jack is providing clean power, +5.09, +12.09, and no difference in grounds. I see no bent pins, any obvious issues.

There is one drive that has survived this logic board, a 426MB Seagate with active termination. But even it requires the (terminated) Zip drive on the external port before it will come up. The logic board has damaged two Apple-branded Quantum drives.

The Seagate has jumpers to select termination power from itself, from the bus/host, etc. I am not sure which is correct for Macintoshes, and whether it matters if it's internally or externally attached. (I suspect if I choose the right setting, the Seagate will work without the Zip drive.)
 
Just to complicate things, on my recent IIsi restoration a leaking cap had eaten through the 12V rail so I had no power at the HD power jack either!
 
Addicted said:
I was about to ask about SCSI termination power. Cool that a topic opened up about this.

Short form:

Any good references out there on the web about SCSI termination? Any ideas how a logic board can permanently damage a SCSI HDD?

Long form:

I have a logic board that seems to fry SCSI HDDs. I can take a newly-found SCSI HDD and attach it to the internal SCSI port, boot the system from an external Zip drive, and initialize/format/test the new SCSI HDD using 7.5 Drive Setup. But once I disconnect the new HDD, no system can use the HDD again.

Once affected, an HDD spins up, spins for about two seconds, then spins down. FWB Toolkit reports that the drive responds (FWB and SCSIProbe can both access the manufacturer data page) but nothing can start the drive. FWB reports "Check Condition" errors on the damaged drives. Drive Setup does not count the drive as present (doesn't find it at all).

The logic board's internal HDD power jack is providing clean power, +5.09, +12.09, and no difference in grounds. I see no bent pins, any obvious issues.

There is one drive that has survived this logic board, a 426MB Seagate with active termination. But even it requires the (terminated) Zip drive on the external port before it will come up. The logic board has damaged two Apple-branded Quantum drives.

The Seagate has jumpers to select termination power from itself, from the bus/host, etc. I am not sure which is correct for Macintoshes, and whether it matters if it's internally or externally attached. (I suspect if I choose the right setting, the Seagate will work without the Zip drive.)
Click to expand...
I saw similar behaviour on my IIsi. In my case I had a PiSCSI attached to it. The drive spun up for a couple of seconds, the spun down. And not back up after reboot. I haven't tested it on another Mac, yet, though.
 
Is it possible to bodge termination power to the SCSI port on an IIsi? I have a MacSD, they do not have a berg connector to supply termination power.
 
JC8080 said:
Is it possible to bodge termination power to the SCSI port on an IIsi? I have a MacSD, they do not have a berg connector to supply termination power.
Click to expand...
The IIsi should already have termination power. At least on the external port it is supplied via D1, L1 and F2 - it stands to reason that the internal is connected the same way. If not, run a jumper from the DB25 pin 25 to pin 26 on the 50way header.
 
GRudolf94 said:
The IIsi should already have termination power. At least on the external port it is supplied via D1, L1 and F2 - it stands to reason that the internal is connected the same way. If not, run a jumper from the DB25 pin 25 to pin 26 on the 50way header.
Click to expand...
Thanks for the info.
 
Good to know, thank you, that header diagram is helpful. You use an external source to power the MacSD USB port in your IIsi? Or you tap into 5V internally and feed it to the MacSD USB port?
 
GRudolf94 said:
The IIsi should already have termination power. At least on the external port it is supplied via D1, L1 and F2 - it stands to reason that the internal is connected the same way. If not, run a jumper from the DB25 pin 25 to pin 26 on the 50way header.
Click to expand...
I did this and it was effective, however I was only getting 4.1V for term power at the MacSD. It worked fine, but I don't know if it is ok to run it on voltage that low. I scrounged an old USB2 -> mini USB that I am going to splice into a Molex connector to pull 5V internally.

I am having some odd audio issues when the MacSD installed, I'm going to start a new thread about those.
 
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