The immortal 1984 Macintosh (restoration diary)
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The immortal 1984 Macintosh (restoration diary)
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August 22, 2026
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After a long pause of a year and a half, I finally managed to complete a modest new restoration project this summer.
The goal this time was to restore an original Apple Macintosh 128K (1984) for display and daily use in an office environment, where it will serve both as an educational curiosity and a source of entertainment and relaxation for employees.<br>However, there is a hidden contradiction in this double purpose—educative historical significance and entertainment capabilities—that pose a challenge: the original 128K Mac, while a major technical accomplishment for the time, wasn't actually useable. Its memory was far too limited for any meaningful application, given that the bitmapped display and fairly sophisticated operating system—for the time—occupied most of the 128KB. It also came with just a single 400KB floppy disk drive. Worst of all, it couldn't be expanded with extra memory or a hard-disk drive, so very little could be done with it as far as entertainment goes.<br>While later Macs addressed all of these limitations, they don't have the appeal and historical significance of the very first one, which translates into an impasse: should I go for historical significance or the ability to actually do something with the device?<br>Luckily, a compromise was possible: I sourced an original Macintosh 128K from 1984 that the original owner upgraded to a Macintosh Plus in 1986. The resulting machine is still a vintage original, but also has 1MB of memory and a SCSI port. Together, these features support a fairly extensive library of games that is more than sufficient for my purposes.
The unit I sourced had a lot of mileage: it had been used daily in a psychology practice from 1984 to 2008 (!). Beyond the 1986 upgrade to a Mac Plus motherboard, it had also never been serviced. The CRT had severe burn-in (in the photo below, you can even read individual words!), the battery had leaked and ruined the battery compartment, the case was severely yellowed, and the gears of the floppy eject mechanism were broken due to plastic deterioration over time.
I sourced another CRT with hardly any burn-in, and used it instead:
I then started the restoration proper with the analog board, which contains both the power supply unit and the CRT driver circuit. Both circuits use a lot of electrolytic capacitors, all of which are 42 years old now and probably leaking both electrolyte and DC.
In such cases, even when the caps are still within spec, soon they won't be. For a machine that is meant to be used daily for the next few decades, a recap is thus the first order of business. I used regular ESR caps (i.e., high-ESR for modern standards) on the power supply's secondary, to prevent a higher current inrush upon power up than this somewhat primitive circuit can cope with. I used low-ESR caps everywhere else for optimal response times.<br>As mentioned above, I also had to replace the battery compartment altogether, due to vintage battery leaks that led to severe corrosion.<br>And as can be noticed in the photo above, the epoxy potting of the flyback transformer was showing unambiguous signs of degradation (it becomes dark brown and brittle, as opposed to the original soft cream color), even though there wasn't yet any obvious corona discharge. See the close-up below, made after I removed the original flyback:
Once again, as this machine will be used daily in an office environment, replacing the deteriorated flyback before failure was a must. I did so using a new-old-stock unit of higher specifications and build quality than Apple's 1984 original.<br>Some impressions of the recapped board, with the new flyback and battery compartment already installed, are shown below.
Here's a close-up of the new flyback transformer, showing pristine epoxy potting:
Notice that I replaced the infamous line-filtering Rifa caps (very prone to dying with a bang and filling the room with acrid smoke) with modern safety caps, which—if they ever fail—fail open and don't cause short-circuits.
I then checked all semiconductors in-circuit, insofar as possible. None were obviously bad, but I preemptively replaced a few for durability. I started with the main switching transistor in the power supply (a C3153), which is one of the most stressed parts in the entire board.<br>I replaced it with a significantly higher-rated modern equivalent (a BU2525AF-PHI, rated for 800V, 12A and 45W), which also has the added advantage of having no conductive tab, thereby requiring no separate insulator between the transistor and its heatsink (in the original, the tab was the collector, so a mica insulator was used in between the transistor and its heatsink). I made sure to refresh the heatsink compound for optimal thermal conductivity.
Three other parts are known to be severely stressed in...