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Confounding Macintosh SE/30 booting behavior


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I recently bought a recapped Macintosh SE/30, and I don't understand the way it's been behaving. Sometimes it will boot to the hard disk and sometimes it will just show the floppy icon (sometimes with the flashing question mark and sometimes without). Sometimes I can get it to boot from an external SCSI2SD and sometimes it won't. It has System 7.5.3 installed by the seller and when it boots it seems fine, but half of the time it doesn't boot beyond the floppy icon. I'm not very familiar with using 7.5 on a compact Mac like this so maybe I'm overlooking something basic. I have selected the internal hard disk in the Startup Disk control panel. Any ideas?

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When it shows the floppy icon have you tried booting it from the floppy? The SCSI chip is adjacent to three capacitors so that can result in the type of trouble you're seeing. If it can boot form a floppy disk after showing the flashing question mark it seems like that could point you in that direction.

 

For one of mine I desoldered the SCSI IC and cleaned under it to resolve similar issues. Mine would actually stop booting once it warmed up. It's possible that the person who recapped this board just didn't clean it well enough and a soak in IPA would be good enough.

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It will attempt to boot from a floppy, but I get a bomb error when it gets to the desktop. But the only boot floppy I have on hand is one I've used with other machines, and it is for System 6.0.8.

 

Is it normal for the floppy icon to be displayed without the flashing question mark? Like I said, sometimes it will flash and sometimes it just says there on the screen (the cursor is movable so it's not frozen).

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Usually (I cannot always say never), any 6.0.8 disk will start an SE/30. This is a rather strange one. It sounds like something may be funky with the VIAs or something that works with both the SCSI and Floppy circuits. I'm blindly guessing here, though.

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I did some more experimentation and I only get the disk icon without the flashing question mark when I have the external SCSI2SD attached. I unplugged the hard drive cable and it seems to allow it to boot from the SCSI2SD every time, so I'm wondering if it's some kind of SCSI configuration error. But it has worked sometimes even with the hard disk attached, which I can't figure out. And I still don't get why it won't boot from its own internal hard disk most of the time, even if nothing else is connected. I might just leave the hard disk disconnected since it's fairly loud anyway, but I don't really like the idea of not knowing what the issue is. 

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So after unplugging the internal hard disk everything seems to be working as I would expect. I am able to boot from the external SCSI2SD and I can also use a Floppy Emu at the same time. The boot floppy that caused the bomb error still does not work, but I make a copy of the System 7 Disk Tools and was able to boot from that with no problem. 
 

What are the possibilities for things that could only affect the internal drive like this? Could the drive itself be the problem?

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The external version uses a different connector so I’m not sure how I would do that. Is there a converter or something? Sorry, I really don’t know a lot about SCSI.
 

I could possibly take a drive out of one of my other machines and try that. I think could still complain to the seller of the machine if I can prove the drive is the culprit

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I'm sorry, I didn't realize it was a 5.5. I always figure people have SCSI wires and such; that is my mistake. Yeah, you'd need an adapter. You can always try the other machine's drive for sure. I'd give that a go.

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the internal and external sci ports on the mac se/30 are electrically connected together so it shouldn't matter if you use the idc50 pin connector on the motherboard or the db25 external plug, those old 40/80mg drives often fail and/or get gummed up inside and stop working/working properly. Ive had similar issues awhile ago when repairing my 'spare parts' se/30, that drive would sometimes work and i was fortunate enough to be able to at least make a back up onto a zip disk before it just failed completely. it no longer works and one of the IC's gets very hot.....

a quick sanity check would be to connect that drive to another mac just to double check if it has similar symptoms but from what you've described its most likely the drive is the issue

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it it runs the external scsi2sd and boots it then your scsi controller is fine, again id recommend trying that hdd on another mac to be double sure because the only other thing then would be a damaged trace going to the idc50 pin internal hdd connector and while my se/30 isn't open in front of me atm im pretty sure the traces go from the 53c80 scsi chip to the idc50 and then to the db25 connector so its be a bit strange if the internal connector doesn't work but the extra one does

i have a old 700mb scsi drive in mine but im going to replace it with something like the scsi2sd myself when i have the spare cash as those old scsi drives are darn noisey :)

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The internal SCSI2SD arrived today and it seems to be working perfectly, so I guess it was just the hard disk itself acting up. Since my SE/30 now has a transparent case, I'll be leaving the disconnected hard disk in there just for looks, and I have the SCSI2SD kind of resting on top of it. Thanks for the help everyone.

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