Just a report on my fix of a Mac SE/30 with strange screen artifacts

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Joined: Jul 31 2009
Posts: 2

Hi all,

This message is just to share my experience. Maybe it is of use to others.

I found a SE/30 in the trash, plugged it in and saw that it almost worked. The screen displayed weird repetitions of 4 times 4 lines - but, reading between the lines, the system booted and worked ok. Figured that 2 address lines of video memory (bits 8+9) were stuck to 0 or another constant value. Found no such artifacts mentioned on the internet. Unscrewed the thing and started to analyse the motherboard, which had nasty corrosion from leaking electrolytes. Figured out that the 2 video memory chips (D41264C-12) are supplied with 2 times 8 bits of addressing information on pins 9-11 and 13-17 (not in that order), where RAS (row addr strobe) and CAS (col addr strobe) are used to tell the memory chips which part of the address is given (effectively a form of time division multiplexing). Found out that the four 74F253 chips are used to multiplex the 16 bit addr onto the 8 bit time divided channel (2 bits per 74F253). While trying to find the source of the 16 bit address on the board (seems to be the 2 TIT chips) realized that the most logical explanation would not be that two adjacent address lines went short with ground, but instead that one Select Input line of on of the 74F253 multiplexers was probably disconnected by corrosion. (pin 2 or pin 14) Which, when measured, turned out to be correct!

Attached (and below) see an image of the artifacts. (the horizontal bars are camera artifacts)
apple 4x4lines artifacts.jpg

I replaced the Li-battery and all 11 electrolyte capacitors, cleaned the board with alcohol, restored the corroded print line using a single strand of some stranded copper cable, subsequently dried the board in my favorite kitchen appliance, and it now works like a charm! Sound has appearantly been restored as well in the process (only being a mac user since the MacBook Pro, I didn't know what sounds to expect when turning the device on). A minor issue was that before the fix sometimes the system would not come up properly and display weird stripes (simasimac?) but now that is gone completely. It always boots up immediately. Also the screen had some noisy interference which has vanished completely.

I'm currently in the process of obtaining a network card to get the thing connected - maybe I'll get back here for advice on getting the thing going.

I think I know the answer to this one, but since you never know: is there any way to get an ms-dos style drive to write 800k floppies?

Another one: Has anyone had any luck on writing to the scsi harddisk in Linux using a simple isa scsi controller?

Kind regards from Amsterdam,

M.

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Dog Cow's picture
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Joined: Dec 11 2008
Posts: 468
Re: Just a report on my fix of a Mac SE/30 with strange screen a

mvds00 wrote:

is there any way to get an ms-dos style drive to write 800k floppies?

Probably not. PC floppy drives got only 720KB because the motor maintained a constant speed. Mac floppy drives got 800KB because the motor would speed up or slow down depending on what track the drive head was positioned over.

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Joined: Jul 31 2009
Posts: 2
Reading 1.44 mb disks on SE/30

Again, to whom it may concern:

I just found out that the SE/30 is able to read 1.44 MB formatted (MFM) disks, the point is that it should be mac-formatted, as in having a Mac-filesystem. The native System 6.0.3 doesn't come with anything that understands FAT. That means that hardware-wise the Mac SE/30 can handle the very same floppies you put in your everyday pc.

Good thing I figured that one out...

(note: I'm not sure if my Mac SE/30 had a drive upgrade to this end, or if it came this way by default)

Dr. Webster's picture
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Joined: Dec 19 2003
Posts: 1687
Re: Reading 1.44 mb disks on SE/30

mvds00 wrote:

(note: I'm not sure if my Mac SE/30 had a drive upgrade to this end, or if it came this way by default)

If memory serves, all SE/30's shipped with SuperDrives. The SuperDrive was an option on later SE models.

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