Upgraded 512K - my first Mac since 1995!

[bigmessowires]

Woohoo! I've got a working Mac 512K, my first Mac in over a decade!

I purchased the 512K system yesterday from a woman who recycles electronics. It booted to the question-mark disk icon, but she didn't have any disks so there was no way to test it further. Being in semi-unknown condition, I was able to get it cheaply.

My next task was to create a 400K disk with System 4.1, which is the newest this Mac will run. I went to a nearby electronics surplus store, dug around through every box and barrel, and scrounged up 11 double-density disks suitable for 400K/800K Mac use. Then I borrowed a friend's SE/30, planning to use it to create the 400K disk for the Mac 512K.

Somehow I thought the SE/30 had ethernet, which it definitely doesn't, so now I had a new task to get the disk image to the SE/30 somehow. I planned to write the 400K disk image .dsk file to a 1.4MB high-density floppy from a PC, read that with the SE/30, and then use it to create the 400K System 4.1 disk. But the SE/30's floppy drive was flaky-- it wouldn't recognize that a floppy was inserted unless I first ran Norton Disk Doctor. Huh?

I then encountered a more fundamental obstacle-- none of the PCs I own actually have a floppy drive. So I went to a large computer/electronics store, and asked where I could find a floppy disk drive. The youngish store employee looked baffled. A what? After a few exchanges back and forth, he admitted "I don't know what that is." I can understand they might not sell them anymore, but to not even know what a floppy disk is??? Now I feel old.

Ran back to the surplus electronics store, and pulled an old floppy drive from a pile in a dingy cardboard box. Got it installed in my PC, only to find I don't have a 3.5 inch drive sled in my PC case, so I left it dangling loose. After many false starts, I finally discovered that the program WinImage will write Mac 1.4MB floppies from .dsk files. So I finally established all the links in my chain of computing technologies reaching from the present back to 1984. Wow.

I was ready to create the 400K System 4.1 disk, when I noticed that the Mac 512K has a SCSI port, labelled "Brainstorm SCSI", that looked like an upgrade. I grew suspicious that this Mac 512K had been upgraded to a Plus-like configuration, and so decided to try making an 800K System 6.0.8 disk first. Made a 1.4MB 6.0.8 disk on the PC, put it in the SE/30, waved some dead chickens to force the SE/30's flakey floppy to work, and copied the 6.0.8 disk contents to the hard disk. Then inserted a DD floppy, waved more dead chickens, and copied an 800K subset of the 6.0.8 startup disk to the DD floppy. Finally put the 800K floppy in the Mac 512K, and... Happy Mac!



Clearly this 512K has been upgraded. It obviously has an 800K drive, since it read my 800K boot disk. Once I was able to boot it, I discovered that it has 1MB RAM. And there's that SCSI port-- I don't have anything to test it with, but I assume it's not just ornamental. I don't know if this was the official Apple upgrade path from the 512K to the Plus, or some aftermarket upgrade. Once I get the tools to open the case, I'll take a peek inside and see what I can learn.

Here's a photo of the back panel, showing the blue "Brainstorm SCSI" connector above the power switch:

 

[LCGuy]

Thats definitely a third party upgrade - Brainstorm upgrades were pretty popular back in the day. The official Apple upgrade involves replacing the 512k's 400k drive with an 800k drive, and replacing the logic board and rear case bucket with the same items used on a Plus, essentially turning it into a Plus.

 

[bigmessowires]

From what I can tell, the Brainstorm upgrade was a 16MHz CPU upgrade for the Mac Plus. Do you know if they also offered 512K SCSI upgrades, or maybe this 512K was upgraded to a super-16MHz Plus?

Until I can open the case and look inside, is there any software I could run that would tell me if I've got a 16MHz CPU in there?

 

[bigmessowires]

Well TattleTech says it's an 8MHz Mac Plus. But I bet it's just pulling the CPU speed from a reference table, not actually measuring it.

Oh man, I had forgotten how painful disk swapping was. I think I had to do about 15 disk swaps to launch TattleTech. And that was after 20 minutes of ferrying files between disks on two other computers just to get the TattleTech program onto an 800K disk.

 

[trag]

Brainstorm's 16MHz 68000 upgrade for the 128K/512K/Plus was a stand alone upgrade. It didn't include a SCSI port. That's not to say that they didn't make a combined CPU/SCSI upgrade.

There were many just-SCSI upgrades for the 512KE ('E' means the 512K has Plus ROMs). So you may have two upgrades: SCSI and memory, or one combined upgrade. Or conceivably three upgrades, SCSI, memory, CPU.

Adding a memory upgrade and a SCSI port upgrade to the 512KE was very popular back in the day.

 

[bigmessowires]

I got the case open today to see what's inside. It's the normal 8MHz 68000, with a 1MB RAM upgrade, and a Brainstorm card with 128K ROM and SCSI upgrade. The Brainstorm card fits right into the motherboard ROM sockets, and has two new ROM chips, as well as some stuff I assume is for SCSI, and a SCSI connector:



The RAM upgrade uses two stacked DRAM chips in each spot, with all the pins soldered together except one, which I'd guess is the chip select pin. It sits in some kind of motherboard overlay plate that lies on top of the motherboard. This plate also contains an additional chip next to the CPU, where I believe the normal Mac motherboard is empty. Probably a modified address decoder? Check out the stacked DRAMs:



Both the logic board and the analog board look pretty clean, and I don't see any evidence of capacitor failure. Is there any reason to monkey with replacing the capacitors? I'd rather not, if it's not necessary. A couple shots of the analog board:





Ideally I'd like to return this Mac to its original state as an unenhanced Mac 512K. I could probably make new ROMs with the 64K ROM image and put them in the ROM sockets, but I don't think I can undo that RAM upgrade. And I'm not sure what a 64K ROM would do if it found itself in a machine with 1MB of RAM.

 

[olePigeon]

Wow, nice score. Looks to be in great physical condition as well.

Just in case you wanna make it look new: http://retr0bright.wikispaces.com/

 

[mcdermd]

To reverse it all, you would need to remove/desolder those RAM sockets, solder in proper DRAM chips, remove the mux board, and put in the proper 64k 342-022x-x ROMs. I had to do the same thing to a 128k board I had.

If you have a EPROM burner, you could probably ask someone for a ROM dump of the 512k's 64k ROMs.

EDIT - almost forgot - you'll also need a 400k drive and ribbon cable if you have an 800k drive with a yellow-striped cable.

 

[H3NRY]

Some people want absolutely factory original. Others want a maxed-out example. Maybe you can find someone who has a vanilla 512k who will swap boards with you. That would give him a stock-looking 512k that works like a Plus, which is a much more useful Mac. The Mac you have now is a pretty good upgrade, and is a lot rarer than a stock 512 or 512e. For the Mac cognoscenti, you can show off the upgrade. The general populace won't know the difference and won't be impressed anyhow. :beige:

 

[jongleur]

I agree with H3nry, the upgraded machine of the period to me is as important, and probably rarer than the clean skin equivalent.

I've got a 512K, stock, that I've actually purchased a RAM upgrade and SCSI kit to upgrade it, and hopefully I'll have a SCSI Rodime 20MB external drive soon. To me upgrading is faithful homage to the period of the machine.