Macintosh 512k restore

[eric]

Hello!

For #Marchintosh2022 I've decided to finally come back to a project that has been on my bench for a long time - my 512k! I picked it up locally last year on ebay for $90.

My goals are:

• Fix the floppy drive
• Install the ROMinator I got from @Kay K.M.Mods
• Clean up the case

Issues:

• Floppy attempts to read and ejects disk
• Screen burn in (not bad enough to matter much though)
• Screen is dim at full brightness
• I took out the case screws a year ago and forgot where I put them!

Tested so far:

• 12/5/3.3 on the floppy port all are right on.
• Battery removed long ago
• Boots with FloppyEMU fine

Floppy

Not sure where to start here. If I move the head from it's starting position and insert a disk it does move itself back to the start position. Do other floppy drives work in the 512k? I could likely find an 800k around here in a working condition, just not sure if it's compatible.

Here's a video of the current floppy behavior with a known good disk.

While I wait for some guidance on the floppy I'll start the ROMinator install!

 

[ScutBoy]

Pretty sure an 800K drive in there will look and work as a 400K drive - it will only write data to the one side of the disk.

It might not physically line up with the slot, though; it's been a while and I can't remember...

 

[Patrick]

I could likely find an 800k around here in a working condition, just not sure if it's compatible.

they are but you will only have 400k. HOWEVER, after you install Kay's mod it will turn your 512k into a 512ke . which means it can use the full 800k if you have that drive. (at that point you have the ROM of a plus)

so without mod: drive treated as 400k even if its 800k. with mod, treated as 800k.

i've never been successful in fully restoring a floppy drive. stupid Mistakes i've made.
1. trying to clean the heads with qtips. i don't know what i was thinking. I was just going to town with cleaning everything i guess. idk.
I got one of this disk cleaning floppy things off of ebay. Where it looks like a floppy, you add some 99% and put it in the drive. So i'm going to use that instead now.

2. shorting out the drive. I keep wanting test the drive before i fully put the drive back in teh cage or in the computer. However, that leads to me accidentally touching the drive with the frame of the Mac or other metal.

Kinda funny that i was most worried about recapping the logic and analog boards, (and doing that mod) but in actuality the most trouble i've had was restoring floppy drives.

If you can restore the 400k i say for for it. it might not be that useful. but there is not many of them left and they are kinda neat from a history standpoint.
However, if you are modding the 512k anyway. Might as well put in a more useful 800k drive.

 

[Volvo242GT]

Same thing with the later Sony MP-F75W FDHD drives. A stock 512 will consider it a 400K drive. A 512Ke will think it's an 800K drive.

If the 400K drive uses a zero track sensor like the later drives, it might be worth trying to adjust it and see if that causes it to read a known good 400K floppy.

-J

 

[eric]

Well I got the ROMinator installed but no sound now. Can start right up into the ROMs embedded OS but no chime nor sound from games or the system control panel.

 

[Patrick]

i had the same problem. check your bodge. i think it might be the brown wire. or maybe the red wire? (its not the yellow one)
sorry i forget exactly WHICH one it was. but it was one of those 3 on that one side that caused audio problems on mine.

maybe i just don't know how to do this. but i had a hell of a time to sodder the wires onto the pins and get a good connection without bridging. ( i did eventually. but man there gotta be a better way)

 

[eric]

Well there is sound from the headphone jack so something between the speaker and mac. I see this thread https://tinkerdifferent.com/threads/no-sound-on-mac-128k.206/ has a few ideas.

 

[Patrick]

oh... then agree its not the mod.

i'm the OP on that thread. and i have not been able to fix it. Note that i did NOT have sound on the head phone jack. but that could be because the Jack itself was rusted.

let me know if you fix it. because i haven't figured out why no sound on my 128k.

 

[eric]

Phew, luckily some detoxit and working the headphone jack a few times brought back sound. Just bad timing I guess. Now to put everything back to gether and find a floppy drive for it.

 

[eric]

Got a 800k drive that works, but it is EXTREMELY slow - external 800k is fast. It took 3 or more minutes to boot to the Finder. Tried another 800k internal drive it was slow as well. Both sort of unknown - eg just in a box I got so I'll pull the 800k from my spare good Plus and see.

 

[Volvo242GT]

I found that when I was trying to get my Plus to boot a floppy that when I bumped the zero track sensor's board, it booted up without issues. Put the drive away for a couple days after testing the computer out, then decided to install it in the SE, so I could try to copy some files over to that computer's hard drive. Had gone back to being very slow and iffy about loading data. Wonder if you're having the same problem with the two drives you tried internally.

Another alternative, is if you have an extra known good FDHD mechanism, install that into the external drive, then take the 800K mechanism from that and try it internally. If it works properly, then just use it. If not, I'd check the 20-pin cable to make sure that it's the correct one. Apple did use two different cables on the 800K drives. One had a red stripe, the other had a yellow stripe.

 

[Paolo B]

I would not alter the hardware of the 512k and keep it as original as possible. It’s the first “usable” Mac, there are so many things you can do with it without upgrading it to something it was not.
As for the 400k drive, I personally love them, they are so “musical” The zero track alignment procedure is the same as with the other drives, just the hardware is different.

 

[eric]

Fixed one of the 800k drives by adjusting the 0 offset just a mm. Now fast. Just need to fix the eject motor continually ejecting (just pulled it off to test) and a full clean and lube.

 

[Patrick]

Fixed one of the 800k drives by adjusting the 0 offset just a mm. Now fast. Just need to fix the eject motor continually ejecting (just pulled it off to test) and a full clean and lube.

that might be a problem with the cable. I forget the deets. but you either want the cable that has a red stripe. or the cable that has the stripe be yellow.

so maybe try the other cable if you have one and see if it fixes the continually ejecting problem.

 

[Volvo242GT]

Looks like if the drive has a label with red writing on it, you want the yellow stripe cable (or one without a stripe). If it's with black writing on the label, it uses the red stripe cable.

-J

 

[Patrick]

and so. if you are moving drives around to different computers, keep the cable with the drive. (not the computer) ?

 

[Volvo242GT]

Pretty much.

 

[eric]

Seems the yellow striped one has pin 9 disconnected (per reading on BMOW's site) - I have one coming as I dont want to cut my current ones.

I've made some mounts to properly mount the 800k disk in the 400k housing/ I'll share the files when I get everything together, but it's pretty simple - only took 2 prints to get right

Hopefully then I can wrap up this months long project!

 

[eric]

I can validate now disconnecting pin 9 on a red cable will stop the continual eject. Now to button it all up

 

[eric]

So... after all that - the 400k drive is good - it was the cable that was bad that came with it! on a whim as I was putting it all back together I thought I'd give the 400k drive one more shot (after knowing it failed just days ago) with my modded cable - Formatted a disk right away. Gah!

Now buttoned up with the original 400k drive working & Rominator.