If you dabble with old computers, then you know the power supplies can fail just as often as the computers themselves. In the case of classic Macintosh computers, Apple didn’t use any kind of standard PSU, so buying new replacements isn’t possible. When a classic Mac PSU fails, the options are to recap and rebuild it, or make an adapter for another type of power supply. PC-style ATX supplies are cheap and readily available, and they offer the same +12V, +5V, -12V, and standby power outputs as Mac supplies. Wouldn’t an ATX-to-Mac PSU adapter be nice?

George Rudolf designed this simple ATX adapter and shared it on GitHub. It coverts a standard ATX 20-pin connector to the 10-pin connector found in the Macintosh IIcx, IIci, IIsi, IIvx, IIvi, Performa 600, Centris/Quadra 650, Quadra 800, and PowerMac 7100.

Aside from the different connectors, there’s also one small bit of active electronics on the adapter: an inverter for the ON signal. Classic Macs and PCs both support soft power, where the computer can be turned on from the keyboard or via software instead of with a hard on/off switch. This requires a power supply enable signal from a circuit using standby power, but the polarity of the ATX enable signal is the opposite of the Mac. Inverter to the rescue.

I was able to get 20 adapters assembled and shipped from JLCPCB for the princely sum of just $1.39 each. The connectors had to be sourced separately, but they’re readily available. Soldering the connectors only takes a few minutes, and they’re easy through-hole components.

I put together one of the 20 kits and installed it in my Macintosh IIci, and it worked great. I think it’s more useful for bench testing purposes than as a full PSU replacement, unless you want to go the extra mile of fashioning custom brackets to secure the ATX PSU inside the case.

For people who are attending Mactoberfest Meetup on October 14, I’ll have nineteen more of these ATX-to-Mac kits as free give-away items. You can assemble the kit right there at the meetup’s repair/work center. One of the Mactoberfest computer demos will also be a Mac IIci powered by an external ATX PSU, so you can see this adapter in action. I hope you enjoy these!

I’ve had an ImageWriter II printer gathering dust in the back of my closet for at least a decade. Originally purchased at the Silicon Valley Electronics Flea Market for 25 cents, it was an obsolete anachronism even then, and the seller was desperate to get rid of it. It came home with me, but I never used it and the printer was quickly forgotten.

Recently I wondered: Will it still work? Have the internal capacitors leaked their caustic innards all over the PCB? Has the ink ribbon from Bill Clinton’s presidency ossified into solid rock? Will those tiny and fantastic dot-matrix pins be stuck forever in tar-like goo?

Somewhat shockingly, I discovered that you can still buy new ImageWriter II ink ribbons in 2023. And also continuous feed paper, with the tractor holes on the sides. You can even find newly-made Mini DIN 8 printer cables, if you know where to look.

It was a journey back in time, straining to remember setup steps that I’d last done 30 years ago. In the classic Mac OS, where is printer setup done? In the vaguely-named Chooser desk accessory? Is it supposed to show me a list of installed printers? Do I need driver software? Which classic Mac OS programs even support printing?

After a few minutes of awkward experiments, I discovered TeachText and its six glorious built-in bitmap fonts, with a choice of six specific font sizes. No Postscript, vector fonts, or arbitrary text size scaling here.

I typed a few lines of text, clicked the print button, and… nothing. Seconds passed, and I felt the sting of failure, but then the printer sprang to life. Hooray, success! I was rewarded for my efforts with a soothing bzzzt-bzzzt-bzzzt symphony of print head movement as the ImageWriter slowly processed the page. And I do mean slowly. Even in normal quality mode, it takes about a minute to print a single page of text. I shudder to imagine the speed of high-quality print mode.

We are spoiled with today’s laser printers that can render a full page in seconds. For now it’s fun to relive the world of 1980s printing. I feel like I should be writing an 8th grade history report about Julius Caesar and then creating Happy Birthday banners with Print Shop.

For people who are attending Mactoberfest Meetup on October 14, I’ll have a computer running MacWrite and connected to this Imagewriter, so you can experience the good old days too. Bring your school history report on a 3.5 inch floppy.

A few days ago I received an urgent note from the facility in China where the ADB-USB Wombat Input Converter is manufactured. They’d just finished assembling 250 new Wombats, and all of them were failing the automated functional tests. Was there a systematic assembly flaw in this entire batch of boards? Or was it a problem with the test apparatus?

I developed the Wombat tester (pictured above with a Wombat riding on top) back in 2017. It’s a board with some simple electronics and an array of spring-loaded pogo pins that make contact with a Wombat board placed on top of it. Grab a newly-assembled Wombat, press it down onto the bed of pins, press a button, and in a few seconds you’ll have a functional test result. Hooray for high-speed testing. The Wombat tester that’s used by the Chinese factory is the original one that I hand-built six years ago.

The tester’s schematic is terrible, and I have no one to blame but myself. It looks like a pile of disconnected components where you can’t really make sense of anything. There are only three chips – everything else is connectors or pogo pins. IC1 is a triple 2-channel analog switch, IC2 is a power distribution switch, and IC3 is a simple quad-OR:

I had only two pieces of information:

1. The functional test was failing ADB communication. USB communication was apparently OK.
2. An engineer found that bridging pins 6 and 7 on IC2 allowed the test to finish successfully.

The engineer suspected IC2 had failed and was searching for a replacement. Given the clues and the schematic diagram, what do you think is the most likely cause of the failure?

IC2 pins 6 and 7 are two separate power supplies: one that’s normally supplied by the ADB host, and another that’s supplied by the USB host. Only one should be active at a time, so bridging them together is not a valid test. Because bridging helped the failing ADB test to succeed, it suggested maybe the ADB5V supply was not turning on when it should. Yes, that could be due to IC2 failure, but could also have other causes.

The ADB5V supply is enabled by the control signal /ADB5VON at IC2 pin 3. That signal comes from the quad-OR gate at IC3, so maybe that was the source of failure? The quad-OR is also responsible for generating the USB power supply control signal. Both signals are dependent on three signals named UNK3, /UNK3, and GNDOUT. Because bridging the IC2 supply pins helped somehow, we can probably conclude the USB supply was active, meaning that /VBUSBON had to be asserted. If the quad-OR was working correctly, that means UNK3 and GNDOUT both must have been low.

What’s with these UNK3 and /UNK3 signals? Tracing back further, we see that /UNK3 is generated form IC1, where one channel of the analog switch is rigged up to behave like an inverter. The non-inverted signal UNK3 has a pull-down resistor at R2. Ultimately the UNK3 signal comes from J7 pin 3, which is one of the pogo pins. The signal comes from the Wombat board being tested, via the pogo pin.

Hmm… what would happen if that pogo pin were misaligned or broken? UNK3 would be disconnected and floating, but the R2 pull-down resistor would bring it low. With GNDOUT also low, /VBUSBON would always be asserted and /ADB5VON would never be asserted. The ADB power supply would never turn on, the USB supply would always be on, and the behavior would be consistent with the observed clues.

Mulling this analysis over a cup of coffee, I replied to the factory: “Check if pogo pin 3 at J7 is bent”. Their response came the next day: “Steve, you are really a professional engineer! The guess you made is correct. After trying again, the tester board started working normally.”

Success! That was a very satisfying fix, based on minimal information and without physical access to the faulty circuit.

The Mac ROM-inator II is back in stock – get yours now at the BMOW Store. The ROM-inator II is a replacement ROM SIMM for Macintosh II series computers and the Mac SE/30, adding a bootable ROM disk, 32-bit cleanliness, HD20 hard disk support, and more. Read more about it at the project’s home page. This is the 1.27 mm (0.05 inch) custom SIMM thickness that works best in finicky SIMM slots like those found on the SE/30.

 
Policies and Partnerships

The Macintosh ROM SIMM landscape has changed significantly since I started selling them in 2016. At that time, BMOW was the only vendor making and selling custom Mac ROM SIMMs, and the “product” was a combination of hardware and software. The hardware was the SIMM PCB and flash memory chips, while the software was a unique base ROM implementing on-the-fly decompression of a ROM disk image, auto-detection of the memory configuration, a new startup chime, and more. Sales of the hardware subsidized my development work on the base ROM software.

In the last few years, several other vendors have begun selling Mac ROM SIMMs too. Friendly competition is great, but it creates a potential dilemma for me if someone buys another vendor’s ROM SIMM and reprograms it with BMOW’s base ROM in order to get the on-the-fly ROM disk decompression and other features. It could turn into a situation where my base ROM software is subsidizing another competing product. To compound the problem, I didn’t have any clear usage policy or “license” for the base ROM to say whether this type of use was OK. Furthermore my FC8 compression algorithm is free open-source, but the BMOW base ROM which incorporates it is not. This all created a large gray area.

I hope to clarify this now by making the BMOW base ROM image explicitly free for personal use with anybody’s own Mac ROM SIMM, no matter what vendor they purchased it from. This is the simplest and best way of resolving the ambiguity for the benefit of the classic Mac community. I only ask that you don’t resdistribute the base ROM image elsewhere – come back to the BMOW Mac ROM-inator II details page if you need to download the image.

For vendors who might be interested in selling a version of their Mac ROM SIMM that’s pre-programmed with the BMOW base ROM software, I’m happy to partner with you. Please contact me to discuss it. CayMac Vintage and BMOW have recently partnered to bring the BMOW base ROM to their Mac ROM SIMM hardware, which you can check out here. Exciting stuff, and I’m glad to see new energy in this space that will benefit the classic Mac community at large.

The current state of custom Mac ROM SIMM technology is the result of hard work by many people stretching back 20 years: Gamba, Jeff Walther (trag), Doug Brown (dougg3), Rob Braun, myself, and many others. I wish you exciting ROM adventures, friends!

Classic Macintosh fans, don’t miss your chance to revisit the halcyon days of Hypercard, desk accessories, and flying toasters! Mactoberfest Meetup is coming to the San Francisco Bay Area on Saturday October 14, hosted by Big Mess o’ Wires in Belmont California. Bring your classic Macintosh, your 1993 issues of MacUser magazine, your LocalTalk cables, and your test and repair tools. I’ve rented an old church building for the day, with enough space for about 50 to 100 of the Macintosh faithful. Come join the fun! And if you don’t live in California, steal a car and drive here. If you’re in jail, break out! You don’t want to miss this.

This is a meetup, so the main activities will be meeting other classic Macintosh fans and admiring everybody’s collection – hardware, media, collectibles, or anything else. If you feel that you don’t have anything special enough to be worth showing – don’t worry! A common Macintosh running an old popular game can make for great conversation.

What you’ll definitely find at Mactoberfest:

• Rooms full of vintage Macintosh fanatics and crusty old computers
• Display tables, chairs, electricity, bathrooms
• Flea market – Items can be offered for sale at display tables or in the “marketplace corner”. Label your for-sale items with your name and phone number so that interested buyers can text you if you’re away from the table.
• Freebies table – Got anything you can give away for free? Put your donations of extra disk drives, cables, adapters, and peripheral cards here. See something you like? Take it!
• Workshop table – Stocked with soldering irons, tools, a multimeter, and maybe an oscilloscope or logic analyzer. Troubleshoot your broken computers here, or build a kit.
• Kits – I’m donating some ATX PSU conversion kits that are easy to assemble with simple soldering. These kits can adapt a standard ATX power supply for use with the Macintosh IIcx, IIci, IIsi, IIvx, IIvi, Performa 600, Centris/Quadra 650, Quadra 800, or PowerMac 7100.
• Tetris Max high score competition – It’s on! Warm up your wrists, the best score by the end of the day will win a complete vintage Macintosh system, including keyboard, mouse, and monitor. See the contest details and rules.
• BMOW products – Buy any BMOW vintage computer product at Mactoberfest, and get it at the meetup.

What you’ll hopefully find at Mactoberfest:

• A knowledgeable person at the workshop table to advise on repairs or kit assembly
• LAN game competition – I nominate Bolo at 3:00 PM. Start practicing now!
• Spontaneous ideas – System 6 trivia quiz? 2400 baud modem demos?

Please bear in mind there’s no “staff” for this meetup, and you’ll pay no admission fee. There’s only me and my desire to enjoy a fun day with other Macintosh nuts, but I definitely can’t do it all by myself. I need help from you! I’m happy to pay the building rental fee and other costs, but I need you to bring Mac-stuff to show, and to help coordinate some of the activities, and to chill out when things don’t go as planned. Set your expectations for a boisterous ad-hoc get-together, rather than a polished trade show experience, and we’ll get along just fine.

What you should bring:

• Vintage computer hardware, media, and collectibles.
• Extension cords and power strips for your computers – I definitely won’t have enough for everybody.
• Items to sell in the flea market.
• Soldering irons and tools like tweezers, cutters, and magnifiers. Multimeters and test equipment. Capacitors and components for common repairs.
• Odds-and-ends to donate for the Freebies Table – How many old SCSI drives and spare motherboards do you really need, anyway? Stop hoarding them.
• Kits and DIY stuff – Can you donate anything that ‘just needs assembly’, like a microcontroller kit or a set of replacement floppy drive gears? I’ll have the ATX conversion kits, but it would be fantastic to have other DIY stuff too.
• Cool stuff you can donate as prizes for the Tetris Max competition.
• Snacks, water, or drinks – Donations will be very appreciated.

How you can help:

Can you take a turn for an hour at the workshop table, helping somebody to troubleshoot a Sad Mac error code or recap a motherboard? How about organizing the LAN tournament? Or if you have another idea for a fun activity, great! Your willingness to help is the critical ingredient for the meetup’s success.

Details

MACTOBERFEST
Bay Area Classic Macintosh Meetup / Demo / Workshop / Swap-Meet / Tournament / Whatever
Hosted by Big Mess o’ Wires
Saturday October 14, 11:00am to 5:00pm
Belmont, California
(event address is on the RSVP form)

Please don’t forget to RSVP if you’re if you’re maybe, probably, or definitely planning to attend. This will help me keep track of who’s bringing what items, and the likely overall attendance level. The street address in Belmont is on the RSVP form.

RSVP here for Mactoberfest

You’ve got Mactoberfest questions! I will try to answer them. Leave a comment below, or shoot me an email. See you in a few weeks.