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SCSI ports not working on 3 Mac Plus's, confused.

Outlander

Well-known member
When I was boxing things up to put stuff in storage, I dug 3 Mac Plus's out of a closet and tried to turn each one on. One by one, they all turned on, and came up to the blinking disk icon with the question mark. I thought "okay, at least they all still work". So, I hoped on my 9600 and quickly loaded system 7.5.3 on an external 240mb HD, made sure it was bootable, and connected it to one of the Mac Plus's. Sure enough, the Mac plus came on, but the screen stayed blank. "Hmmm" I thought; "maybe a bad SCSI port, or something". Tried Mac plus number two, same exact thing! Number three, Ditto. "WT%" I thought at this point. I then dug out another enclosure and different HD, a 40mb quantum. I loaded it up, same thing. Long story short, I did this with 4 different HD's, tried the Mac Plus std. interleave on the HD's, and still nothing! But as soon as I take any device off the SCSI bus, the blinking question mark comes back on the screen and all the units boot off of a system 6 floppy disk.

The only thing I noticed was that the PRAM battery was dead in all the units, could this make the Mac pluses give up the ghost when any SCSI device is attached? No leaking caps or anything on the motherboards, has anyone seen such a thing before?

Thanks

 

Byrd

Well-known member
Is this using the same external SCSI case? Also, 7.5.3 needs at least 4MB+ RAM, which if your Pluses are stock ...

 

techknight

Well-known member
Yes. you must supply your own termination power. Simple 4.7ohm resistor, and a regular 4001 diode from the 5V rail to the termination pin of the DB25 connector. presto. Simple mod, and it works.

 
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