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| Color Classic SCSI Issues |
Posted by: jdmlight on 2015-07-22 18:31:08
So I inherited a Color Classic from a friend that knows I like fixing Macs. The case is in surprisingly good condition (minimal yellowing, very few scratches, even still has the Quicktime sticker!). It also has 2x4MB RAM sticks, so it's maxed out as far as that goes too.
I have done the following so far:
- New 3.6v PRAM battery
- Replaced capacitors on motherboard
- Replaced hard drive with one leftover from another computer (18gb IBM with adapter to 50 pin SCSI)
It will always boot if I plug in an external SCSI ZIP drive with the termination set to on. But it won't boot without an external SCSI device. I've tried both with and without the "TERM POWER" jumper on the hard drive with no apparent difference.
Any ideas?
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Posted by: Elfen on 2015-07-22 20:08:59
Check of the internal drive has Termination Resistors. If not, find some and put them in.
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Posted by: max1zzz on 2015-07-23 06:55:31
Is that IBM a 80 pin or 68pin drive? 80pin drives do not have termination resistors, and most 80pin -> 50pin adapters don't have them either. So if it's 80 pin you will either need to get a terminated adapter, or a pass through terminator (or there are ones that attach to the external db25 socket) (or you can solder the resistors to your existing adapter )
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Posted by: jdmlight on 2015-07-23 10:38:46
It is a 68 pin drive. I did figure out from this article: http://vintagemacmuseum.com/formatting-old-mac-scsi-drives/ that I should change the SCSI ID to 0. I had it set to 1, which is supposed to be for external devices.
I also figured out that I was looking at the block of pins on the drive backwards, so what I thought was enabling and disabling the termination was actually just changing the SCSI ID from 0 to 1. I have an IBM 24P3688, manual here: http://ps-2.kev009.com/pccbbs/options/32p0743.pdf Also, I figured out that the "TERM POWER" pin is just enabling or disabling power for a terminator, not actually turning termination on or off.
Does anyone know of any 68-to-50 pin adapters with a termination switch? I'd prefer to not have a 25-pin terminator hanging off the back, as I intend to sell this at some point. Or, how hard would it be to solder the termination resistor(s) to the existing adapter? The adapter I have looks like this: http://www.amazon.com/SCSI-68-Pin-IDC-50-Pin-Adapter/dp/B003MMS5KA/
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Posted by: jdmlight on 2015-07-23 16:54:17
I looked around for a while for a 68-to-50 pin adapter with termination, and I couldn't find one. I ended up buying a 50 pin pass through terminator, which hopefully will fix the termination issue. Thankfully these Color Classics have quite a bit of room behind the hard drive for adapters. Not something I can say about the LC II I restored a year ago...
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Posted by: Paralel on 2015-07-24 12:59:27
So, you double adaptered it?
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Posted by: jdmlight on 2015-07-27 17:55:31
So, you double adaptered it? Yes indeed. Drive>68pin-to-50pin adapter>50pin terminator>cable. Just installed the drive with both adapters, and the SCSI cable juuust reaches. But it works! Boots without needing an external device attached.
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