Helping a 512k’ed 128k get back to basics

[LaPorta]

So I’ve got this 128k that way back when was turned into a 512k. This was done by:

- desoldering the 128k of RAM and soldering 512k in its place.

-changing the ROMs to 512ke ROMS, leading to...

-the internal floppy drive being replaced with a standard 800k model.

The original analog board also gave out, but I still have it. It’s a pretty nice survivor overall, being a “Macintosh” and not the latter “Macintosh 128k” badged variety. I obtained it from a friend around 2000 or so, swapping it for a Mac Plus (little did he know!)

Seeing as that it has its original motherboard, id love to revert the RAM/ROMs, but what’s the chance of 

finding 128k RAM chips and original ROMs...or a 400k drive for that matter? I’d also love to get the analog board back up, but I’ve heard the design is for the birds and unsafe.

Any suggestions as to where to start?

 

[tanaquil]

I can't say what the chances of finding the RAM chips are, though I have heard that replacing them is very labor intensive.

The ROMs are easy, they are socketed, and I do see the ROMs for sale on ebay sometimes ($100 or neighborhood). Get the B version, as the A version may have trouble with most 400K drives.

400K drives are also not that hard to find, maybe $50-100. A drive from an enclosure would work, though I don't know if the 400K internal bracket is different from the 800K bracket.

What with the expense & the labor, you might almost be better off pricing an existing 128K on ebay. But if you just want to roll back your existing unit for kicks, it's your party!

Oh, the analog boards are often quite fixable if you just identify the weak points and replace them. All the analog boards from 128K-Plus were basically the same except Plus models tended to be made with components that were more heat resistant, they had figured out the problem by then. All those early macs run hot and a fan like a Kensington System Saver helps keep them cool. The only way I wouldn't fix the analog board is if it had multiple severely burned components, which you can tell by visual inspection. Replacing a burned J1 connector is a pain as I have discovered, you have to rob the part from another board. Ditto the L2. 

 

[Gorgonops]

- desoldering the 128k of RAM and soldering 512k in its place.

There's more to it than that, exactly how much depends on the motherboard revision. On old pre-"Fat Mac" boards you'll find some hackery (often in the form of a piggybacked IC and a few flying wires) to set up the memory decoding for the larger RAM; on later boards I *think* the change just involves some resistor changes and maybe a trace cut? (I'm sure it's documented somewhere.) The RAM chips in a 128k are still relatively easy to find, they're standard 4164s as found in every computer from the Commodore 64 on up in that era. Even Jameco still has them. The thing you'll be missing is the silkscreened Apples that came on most of the originals...

Which raises this point: Literally the only thing a 128k has over a 512k is "collector's value"; IE, by every objective measure a 512k is at least the four times better that its larger RAM size implies. The fact that your computer was upgraded to the "512ke" standard shows that someone actually *used* the machine; the only reason 128k Macs still exist is they represent machines that were thrown into a closets and forgotten about because of how useless they were. Given you *can't* really return the machine to its original state (IE, the soldering on the motherboard, wrong RAM chips, etc, will always be a giveway) I really question the value of doing it. But, well, different strokes for different folks, I guess.

(And seriously, practically speaking there's very little point to downgrade from the 128K ROM to the 64K and to downgrade the floppy drive. You can probably count on one hand the number of obscure copy-protected software titles that only run on the 64K ROM vs. 128k, and for most of those the reason is because of the floppy drive, IE, they use a special disk format that relies on playing with the PWM signal to spin the drive at a non-standard speed, something the 800k drive won't honor.)

 

[Trash80toHP_Mini]

The only good 128K is a hopped up 128K. Almost a totally useless POS as it was originally shipped. Unless you bought the external FDD, a 512K was hard pressed to be productive. The 128K was unendurable without it according to the early adopters I knew at NYMUG. So much for the Steve's all you need in one cute little box concept.

A pristine, original, unadulterated 128K might be worth something as a collectible, but what you have there is a time capsule of what really happened in the Eighties to make the Mac useful for PageMaker and Fontographer, the heart and soul of the DTP revolution. There is no "getting it back to original" once it's been upgraded.

Get yourself an ImageWriter and ThunderScan, the girls will LOVE it! :approve:

YMMV

 

[LaPorta]

Very interesting perspective, guys. I hadn’t thought of it that way.

at the very least, I’d like to get that analog board back up and running.

 

[Dog Cow]

LaPorta, what are the first 3 characters on the Mac's serial number sticker? Second question, what is the copyright year on the motherboard? 1983 or 1984? Third, how do you know the RAM upgrade was performed by swapping ICs and not by swapping the entire motherboard?

Macintosh motherboards with a 1983 copyright year are the original revision with 128K of RAM and they need an additional multiplexer IC added to address 512K of RAM. Beginning with the release of the Macintosh 512K in fall 1984, the motherboard was revised to be the same board for both 128K and 512K RAM configurations. This board has a 1984 copyright date.

Further reading: Fatten Your Mac 512K Upgrade

 

[Dog Cow]

400K drives are also not that hard to find, maybe $50-100. A drive from an enclosure would work, though I don't know if the 400K internal bracket is different from the 800K bracket.

The internal brackets are different.