Putting a PT-65B switchmode power module into an Apple IIe

You might ask why I did not attempt to repair the original power supply (only the usual culprit, the "Rifa" capacitor had exploded / cracked open). The reason, other than the 220V issue which limits the Apple IIe to my lab, where I have a step-up transformer, is that all the electrolytic capacitors in the original power supply are 40 years old, and beyond their safe life span. Which means they all need to be replaced to have a reliable power supply which would not cause more trouble down the road. And unlike some people believe, it is neither trivial nor cheap to replace the electrolytics in a switchmode power supply. They need to be chosen carefully to be suitable for this application, and "normal" electrolytics designed for filter purposes after an AC rectifier just won't do. These are specified for 120 Hz operation only, while the typical switchmode power supply works at more than 100 x that frequency. For electrolytics in switchmode power supplies, ESR at high frequencies (up to 100 kHz or more) and ripple current ratings at higher frequencies are critical, otherwise, they might just overheat and explode. So be warned, don't attempt to replace electrolytic capacitors in switchmode power supplies unless you are competent in this field of engineering. Now, the bad news is that suitable electrolytics are special types which are so expensive that replacing all of them would cost more than a brand new PT-65B. Besides the mechanical issue that none of the modern replacements have the same footprint anymore. Even electrolytics did shrink in size in the past 40 years. This mechanical complication is worse than you might think - the issue is how to bend the leads properly without damaging the seal of the rubber plug. It can be done, but then the next issue is how to prevent them from wobbling around, they need to be glued together somehow. Same reason why "Mean Well" puts white silicon goop in their power supplies to secure larger components, like electrolytics, in place. All this conspires against replacing these old electrolytics in the old power supply PCB. IMHO, it's simply not worth the time, money, and effort.


Apple /// Reset Logic & Apple II Emulation Flaws

I recently ported software from the Apple II to Apple III and encountered an interesting topic. It's a corner case, but in my opinion a typical example. It shows how the Apple III design was sometimes (maybe unnecessarily) complicated. And how features introduced Apple II compatibility issues.

Unidentified 1986 Apple Macintosh Plus Portable / Luggable Industrial Vintage Computer

I just aquired this 1986 Apple Macintosh Like Plus Portable / Luggable Industrial Vintage Computer.

I don’t know much about this machine other than it’s based on a 1Mb Macintosh Plus machine, it’s completely custom made in around 1986 and it does not work.

The machine itself is really unusual as it’s built to a really high finish with injection moulded plastic and really finely cut steel and aluminium, but it doesn’t have a single label on it - nothing to be able to tell who made it and why.

Inside there is a Macintosh Plus motherboard and analog board, with a custom adapted SCSI hard drive, floppy drive and some controls such as reset and either volume or brightness. There is also a serial output on the back, which suggests this had some kind of industrial use.

Has anyone ever come across one of these?



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