A few weeks ago, a buyer of one of my famous 100% tested and burned-in IC Kits for Apple-1 builders (he lives in Sweden, the only Western world country without destructive and tyrannical covid countermeasures, nice !) nudged me into exploring the possibilities of running an Apple-1 from one +5V/-12V/+12V switchmode power supply.
Not that use of switchmode power supplies ("switchers") with the Apple-1 is new, many builders did that, and even I gave some hints in my "Tips & Tricks" pdf on how to use two (or three, if cheap, safe, isolated "wall warts") switchmode power supplies in lieu of transformers, but all these previous recipes were geared to be as foolproof as possible: no modifications whatsoever to the basic Apple-1 motherboard, and all the on-board rectifier diodes, filter capacitors and regulators still in the circuit. This means feeding +9Vdc and +/-15Vdc and this means, alas, no single switchmode power supply to be found being able to provide these non-standard voltages from one unit. So you had to take at least two switchers, one for 9Vdc, and one for +/-15 Vdc, which are readily available as standard off-the-shelf items. Or, for people scared to death from tinkering with potentially lethal line voltages, three "wall wart" type switchmode power supplies, one 9Vdc, and two 15Vdc, again readily available off the shelf.
The irony is that all these solutions typically come cheaper than buying two suitable transformers and paying the shipping costs for these heavy items. And switchers, as long as they are properly insulated, are much safer than transformers. Which have numerous issues, such as being a fire hazard if not surrounded by (several) properly sized fuses. Still, switchers also do have their pitfalls - don't even think of grabbing any "open frame" switcher using the fingers of one hand to move it while it is in operation ! - it will definitely hurt and if unlucky, may kill you. (Don't dare to ask how I know ;-)
Now, the drawback of these previous switchmode power supply solutions was that it ain't just one switcher doing the job. Which is as ugly and awkward and wasteful as having two transformers instead of one (BTW, I have found a few nice vintage looking 110Vac transformers which can run an Apple-1 (or more) from one transformer - send me a message if interested in one of them).
So it was inevitable to explore how to run an Apple-1 from one +5V/-12V/+12V switchmode power supply. Without opening traces and if possible, keeping the original looks of the Apple-1. In the end, the same requirements as with all my other mods: keep the looks and make the mods easily reversible.
Here is the result:
This Apple-1 happily runs from one switchmode power supply, and all the on-board rectifier diodes, filter capacitors and regulators still being there, for correct vintage looks. The only mod to the Apple-1 motherboard was adding three wires on the backside (sorry, no photo yet due to liability reasons). A custom cable to connect the switcher to the Apple-1 also must be made. The switcher suggested by my Swedish fan happens to have the same 6-pin header as the J1 on the Apple-1, so the same type of connector can be used to make the cable. Nice !
This mod also is easily reversible buy just removing these three wires. Then you can plug in the transformer(s) again to feed the Apple-1.
Here are the risks as far as I can see them: make one little mistake when implementing this mod, and - poof ! - your Apple-1 will go up in smoke or, even if no smoke happens, all these precious and rare ICs may get fried (aka "dead") instantly once the power is turned on. Of course, proper procedures can mitigate this risk, but it's definitely not a foolproof mod at all. And, of course, mess with the switcher in any incompetent way, such as blatantly evident in the above photo, you (or a pet, or a kid...) may touch lethal high voltages which may kill all living things - every switcher has a large capacitor on the "hot" side with enough charge to kill a horse, so always put these beasts into insulated enclosures, but allow enough cooling air flow (typically, for the Apple-1, convection cooling is enough). The only reason why I took the risk of not putting this switcher in such an insulated enclosure is that I had to take this (and other) photos to show details which would be invisible if the switcher had an enclosure. So don't follow my footsteps in this case ! Always insulate your switcher, no exception !
Yet another risk is if you have the Apple-1 modded to be fed from the switcher, and you still have a transformer based power supply (see it lurking in the background of the photo ?), and plug it into the modified Apple-1, and power it up, you may instantly kill all these precious and rare ICs again. This time by AC, not by DC, but I was not able to ask these ICs for their opinion which type of death penalty they prefer. I tried to mitigate this risk by putting a red (!) Dymo placard at J1 spelling out "DC ONLY". But placards have the property to fall off or getting ignored. Such as "AUTOPILOT INOP" placards regularly found in small aircraft. Known to be an irresistible lure for curious, cocky and stupid pilots ! And I expect to find a few fools like that also among Apple-1 owners. Which even might sue me for their own stupidity if their Apple-1 is toast due to their own ineptitude or attitude.
This said, and the pros and cons listed, I would like to hear your opinion / comments on this mod. Do you think you could implement it safely ? Do you think it is fit for less experienced builders ? Do you see some other risks / dangers lurking in the mod which I did not list (a trick question, of course !)
Now it's your turn. Comments invited !
- Uncle Bernie