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Macintosh Plus boot problem

Wawavoun

Well-known member
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...

I download 6.0.8 800 k floppy images.
Then from a working SE/30 I made a boot floppy with the 'system tools' image using diskcopy.
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 noticed that the Plus, sometime, even not start to boot and directly eject the floppy with a question mark or cross in the icon.
It is like if the Plus write something to the floppy during the boot because at that point I have to rewrite it into the SE/30 to use it again.

I also try to boot from scsi + bluescsi + a disk image make with minivmac (100 mo blank disk + 7.0.1 fresh install). The Plus dont boot from scsi. I just see the green light flashing rugularly on the bluescsi and the icon waiting for a suitable floppy.

I have two way to search : bad "reading" from the floppy drive or something wrong into the processor board (rec C).

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

I have a second logic board (rev D) which, at the same place, give nothing expect strange sound and fuzzy display at startup.
I already cross memory modules and rom as far as I can with what I have here but with always the same result.
I have no ground clip for this rev D board. Is that important ?

At this point any advice will be helpful. I have a 150 MHz scope etc.. so measure and testing is possible with some indications and help.

Thanks a lot.

Philippe
 

mg.man

Well-known member
I say "successfully" because the SE/30 can boot without error with this floppy
I know it's a pain, but to eliminate the Plus's floppy drive, try removing the drive from the SE/30 and connecting it to the Plus and booting. Even though the Plus does not support the 1.4M (marked 2M) drive, it should use it for 800k disks just fine. Do you have the original floppy drive cable from the Plus? If so, use that cable.
 

Wawavoun

Well-known member
Yes its a pain but I do it !

You are right. With the SE/30 floppy drive the Plus boot well !

Is there something I can do / adjust on the Plus drive ? I have already clean and lube it... Insertion, ejection works well and smoothly.
 

mg.man

Well-known member
You are right. With the SE/30 floppy drive the Plus boot well !
Great! At least you know what needs "fixing"...

Is there something I can do / adjust on the Plus drive ?
Possibly... let me go find the thread and come back... Got back before the Edit window closed... :)

I know there is another thread that talks about stripping / cleaning, but not sure it goes into alignment. This thread might help with the latter...
 

volvo242gt

Well-known member
There is a thread over at the other site (tinkerdifferent) that shows how to adjust the zero track sensor, which is likely your problem.

Alternatively, you can compare the position of the sensor on the FDHD drive and adjust the 800K drive's sensor to exactly the same spot. That should get the 800K drive working properly again.
 

Wawavoun

Well-known member
Thanks for the link ! He give valuable informations...

I can find a spot where the Plus start to boot but I always get this error "illegal instruction" after the welcome message... At other places the Plus directly eject the floppy.
 

mg.man

Well-known member
where the Plus start to boot
Definitely sounds like alignment. It could also be slight friction on the "worm" drive - make sure that's nice and clean and lubricated. Lastly, do you have a (head) cleaning diskette. If not, you can very gently wipe the heads with a 99% IPA-soaked cotton bud. But be very careful, a cleaning diskette would be better.
 

Wawavoun

Well-known member
This afternoon I connect the 800 k drive to the SE/30 and successfully format some floppies.
I also prepare a set for 6.0.8 installation.
Then I reconnect it to the Plus, can boot it and install the system onto a floppy.

So the conclusion : both of the drives are working. One of them or both are misaligned...

It s not easy because at this moment the SE/30 is the only way I have for transferring things to the Plus via floppy...
 
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