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Macintosh Plus boot problem

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Wawavoun

Experienced Member
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May 17, 2020
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Alsace Yo !
Hello there !

Finally I got my scrap rescued Macintosh Plus alive !

The system start, make 'bong' and then display a floppy with a cross or a question mark if I put a blank floppy in the drive...

From a SE/30 I succesfully make a 800 k 6.0.8 boot floppy. I say "successfully" because the SE/30 can boot without error with this floppy.

Putting this floppy into the Plus and he smile and start to boot... then floppy read, head moves etc... I see the welcome message.

But at some point I get an "illegal instruction" or, less frequently, a "illegal address" error... Then I have to restart the computer.

I have two way to search : bad "reading" from the floppy drive or something wrong into the processor board (rom, ram, etc...).

Because the boot start well my opinion is for the second option...

There is another strange thing. I have try to boot from a external scsi drive (made with the SE/30). After power up I can see activity on the scsi drive but the speaker of the Plus really make strange noises (long krrrrr) and the display become crazy... Nothing readable to the screen at all ! This external scsi drive is working well on the SE/30.

Any advice will be helpfull.

Regards.

Philippe
 
If the SE/30 boots fine from the disk and it's giving an Illegal Instruction on the Plus, there's a hardware incompatibility. Where you writing the floppy from? disk image? Install set?
Same goes for booting from the hard drive. If it's working on the SE/30 and not the Plus the system software is running into the weeds.
 
Hi,

The floppy is made with the 6.0.8 800 k "System tools.image" found here :

www.macintoshrepository.org

Mac System/OS 6.x (6.0, 6.0.1, 6.0.2, 6.0.3, 6.0.4, 6.0.5 , 6.0.6, 6.0.7, 6.0.8, 6.0.8L) - Macintosh Repository

All following are English. For international System 6.0 to 6.0.8 (in 29 different languages) and variations, check out the System 6...
www.macintoshrepository.org www.macintoshrepository.org

in the second .sit archive...

I have use diskcopy for duplicate the image to the 800 k floppy.

There is a install script on this disk so it is supposed to be compatible, I think.

Thanks.
Philippe
 
Odd. That should work.
Your floppy drive should also be compatible. The Plus only shipped with an internal 800k drive.
Try another version of system 6, in case something's weird with the disk image itself.
 
Mount the disk image, then use diskcopy to make a new diskimage of the mounted disk. That new disk image it makes can then be made to real disks.
 
The problem come from the floppy drive. I cross them with the SE/30 then the Plus boot correctly !

I have clean and lubricate the drive. The heads look to be clean and touch the floppy surface so...

What can I do more ?
 
was the Plus the system (and perhaps 128 and 512) that had a special floppy ribbon cable designated with a Yellow pin 1 wire (as opposed to later cables with a red pin 1 wire) If so I know those cables are not interchangeable. Are you using the correct yellow stripe cable?
 
The red label on the drive is not what I am talking about, but it sounds like you have the right ribbon cable.
 
The symptoms written in the OP have nothing to do with a bad floppy drive. If the machine is making weird noises and having display corruption when a SCSI drive is attached, there's something seriously wrong with it.

I'd suspect problems with the analog board and power supply, and potentially bad RAM.
 
Hi,

Now the Mac Plus boot from bluescsi and is working well.

The problem with the drive is clearly an alignment question. If I use it alone I can format, write and read floppy.
If I try to cross floppies with the SE/30 then I go into problems...
The SE/30 floppy drive look good because he can read 1.44 MB floppy made with a pc so I suppose it is not too much misaligned.

Now I try to find a way to change this alignment but with some control (like with peelable wedges or something like that so I know what I do).

If you have any advice ?

Thanks.
Philippe
 
If you have any advice ?
Click to expand...
Get another floppy drive.

I don't know how you found the one place on the internet that space-brain linked weird Illegal Instruction booting issues to a track 0 alignment but your absolutely awful troubleshooting skills ruined an otherwise good floppy drive. You do not have the proper tools to correctly realign that drive again. Most people do not have those tools. That drive can't be trusted anymore to reliably read disks interchanged between systems.
Get another floppy drive and beyond cleaning and lubrication, never touch the alignment adjustments, ever.
 
I've managed to realign a drive by repeatedly accessing it while twisting the head motor in increments. This was a PC (PS/2 actually). It's not aligned properly with tools so it would be hard to tell how well it is aligned, but it reads and writes disks well enough to use it. Basically if the drive is useless as is, you don't have much to loose. Bit of a faff though. I would try to get another drive, if possible.
 
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