iiinova — where your digital self keeps evolving

Doug Brown @downtowndougbrown.com · 09/11/2025

Yeah, I think they do. My 550 has a hole for it. So maybe it’s not too risky after all!

Doug Brown @downtowndougbrown.com · 09/11/2025

That’s fascinating! My family’s caddy-loading Performa 550 came with the exact same CD (I still have the CD) and I happen to have a caddy-loading 660av here too! It would be interesting to see if I can replicate the problem here — maybe not in my 550 though, haha. That would be a pain to take apart.

100

Doug Brown @downtowndougbrown.com · 05/10/2025

The bad news: I don't get to share video footage of my IIsi PSU frying. The good news: it's fixed! Even though I wasn't feeling optimistic after the first Q101 and D104 replacement failed, I tried again and it worked. The difference: this time, I didn't try to power it up with the dim bulb tester.

241

Doug Brown @downtowndougbrown.com · 14/09/2025

My IIsi power supply is proving to be tricky. I put in a new MOSFET and Zener, and this at least restored it to a state where it doesn’t blow the fuse when I plug it in. Good +5VSB too. Tried to turn it on, and it failed again and something’s shorted again. :-(

220

Doug Brown @downtowndougbrown.com · 07/09/2025

Answering my own question, I think the transformer might actually be okay? I was worried because of low inductance on the damaged side, but it’s literally just a wire going through the core once. Matching the PCB silkscreen. And it’s on a current sense part of the circuit. Whew…I think…

010

Doug Brown @downtowndougbrown.com · 07/09/2025

It also took out the 18V Zener diode on the gate, and I think it may have damaged this transformer too, which is a major bummer. It’s a custom part, no off the shelf replacement. Why does the PCB silkscreen show an inductor on one side and a straight line on the other?

110

Doug Brown @downtowndougbrown.com · 07/09/2025

I’m not sure if it’s _the_ problem, but this is definitely a problem! This is the main transistor that the riser board controls too, so maybe that’s what was damaged by the bad board.

140

Doug Brown @downtowndougbrown.com · 01/09/2025

This is not a time machine. Blowing the fuse in my IIsi PSU gave me an excuse to finish putting my IIci/IIsi PSU tester into a nice enclosure. Pretty proud of this! First time I’ve made a case like this that wasn’t 3D printed. Although I did need to design and 3D print some internal brackets.

040

Doug Brown @downtowndougbrown.com · 30/08/2025

Got out the toaster oven and built up some IIsi PSU daughterboards today. First two test out perfect. The third…I turn it on and kablooey! Visible spark and F101 blows on my power supply. Dang, this is what I was worried about. Hard to test these without risking my PSU. Hope it’s not shot.

220

Doug Brown @downtowndougbrown.com · 25/08/2025

Okay, my IIsi riser board replica is looking good. Everything will be uploaded to GitHub shortly, and I'll figure out a way to offer them for sale for convenience. As for the failure: it was a bad solder joint on pin 10 of the chip. @48kram.bsky.social had the closest guess and is the winner!

430

Doug Brown @downtowndougbrown.com · 24/08/2025

Built up my first IIsi power daughterboard replica. It looks nice, but it doesn’t work! The power supply immediately shuts off like it’s going into protection. Dang. I did end up with random tiny solder balls here and there from the paste. Could just be a soldering mistake.

5110

Doug Brown @downtowndougbrown.com · 22/08/2025

Remember my research into the “lost” Performa 550 recovery partition? This hard drive arrived today, and it also has the partition! Even better, all the original Performa software is still on it too. This should hopefully solve the mystery of how the partition was originally created.

3285

Doug Brown @downtowndougbrown.com · 19/08/2025

I probably won’t get around to building a replica up and trying it in my IIsi until this weekend, but look what arrived today!

170

Doug Brown @downtowndougbrown.com · 12/08/2025

My tester has voltmeters for all three power rails now. It would sure be nice to arrange it into a clean enclosure instead of a jumble of wires though!

000

Doug Brown @downtowndougbrown.com · 11/08/2025

Getting closer to trying out my replica design…just waiting on PCBs to arrive.

141

Doug Brown @downtowndougbrown.com · 03/08/2025

Someone else did a similar test and found their 5V rail doesn't stay quite as high as mine when it shuts off. More like 1V. I even made a power supply tester and confirmed with no capacitance added to the 5V rail at all, the power supply behaves totally fine and shuts on and off as it's supposed to.

120

Doug Brown @downtowndougbrown.com · 03/08/2025

The 5V rail (pink) is actually keeping a fair amount of voltage -- it's still at 1.2V after 250 ms. After the Egret stops driving /PFW low, it creeps slowly back up toward the (now dead) 5V rail due to the 3.3k pullup through a diode on the logic board. It's reaching the transistor turnon threshold.

110

Doug Brown @downtowndougbrown.com · 31/07/2025

This is maybe the weirdest PCB I've ever laid out. The pad sizes are inconsistent. I had to manually edit each one to match the original. The traces are weird too. I had to make a copper fill for each trace. It was almost like it was hand-drawn originally or something. It's basically done though!

010

Doug Brown @downtowndougbrown.com · 29/07/2025

I'm making some pretty good progress on a Mac IIsi power supply riser board recreation design. With how much effort I've put into understanding the schematics, why not? Plus, having it all in KiCad will make it easier to understand for people going forward.

130

Doug Brown @downtowndougbrown.com · 20/07/2025

Last picture for tonight: scoped the base of the DTC124. It's not turning on until *after* ON/OFF goes low. If I haven't missed a short on the riser board, isn't this potentially a bad M51977FP? Brand new DTC124, it's not being asked to turn on, and 5V standby is good. ON/OFF should not drop to 0.

200

Doug Brown @downtowndougbrown.com · 20/07/2025

Thank you for all your ideas today! I will definitely look at the Zeners. While I had my scope out, I added the main +5V rail as well as the +5V standby rail to my scope trace. Confirmed: the 5V rail does shut off, but then something drives ON/OFF low. Also confirmed: 5V standby stays at 5V.

210

Doug Brown @downtowndougbrown.com · 20/07/2025

I set up to probe /PFW and the ON/OFF pin of the PWM chip. Here is what happens when the IIsi does a Special -> Shut Down. It drives /PFW low, which definitely causes the ON/OFF pin to go high (makes sense so far). But...after it releases it, ON/OFF goes low again. Seems wrong.

120

Doug Brown @downtowndougbrown.com · 13/07/2025

I also think I've solved one mystery about the Bomarc IIsi schematic that confused me. They identified the chip marked "44" as a DTA124, but I think that's wrong. It's not like the others. Thanks to marking code searches, I think I may have identified it as a M51944BML. It looks just like mine.

110

Doug Brown @downtowndougbrown.com · 13/07/2025

I think I've narrowed down the circuitry involved in IIsi ON/OFF control. Pink is GND, bluish purple is the ON/OFF control starting from /PFW on pin 3. I'm tempted to replace the BAS16 and DTC124 since that's what the shutdown signal from the logic board would go through, and they're cheap.

320

Doug Brown @downtowndougbrown.com · 12/07/2025

So I did this yesterday in an effort to fix my IIsi. It works fine, but there's something wrong with the soft power circuit because when I tell it to shut down, I hear the relay click but then it turns right back on. Removing every component and cleaning everything didn't fix it! I'm at a loss now.

130

Doug Brown @downtowndougbrown.com · 01/07/2025

I partially reballed this eMMC chip...by hand. No stencil. Just sticky flux, 0.3 mm solder balls, tweezers, a microscope, and a hot air station. Each solder ball was about the size of a grain of sand. Somehow I did it, and it was enough to read out the contents using my T56 programmer!

030

Doug Brown @downtowndougbrown.com · 23/06/2025

Here are some screenshots of the process of showing the picture in Mac OS 8.1. It doesn't seem to work in Mac OS 9, by the way.

291

Doug Brown @downtowndougbrown.com · 04/06/2025

When the green light is red, it's charging. When the green light is green, it's finished.

010

Doug Brown @downtowndougbrown.com · 03/06/2025

Had a fun little visitor tonight. “Oh hello, I was wondering if you could show me how to get the Tanooki Suit in World 4-5 of Super Mario Bros. 3”

000

Doug Brown @downtowndougbrown.com · 01/06/2025

Oh wow, I forgot I still had this. Unopened Color StyleWriter Pro black ink cartridge. Wonder if it’s all dried up?

000

Doug Brown @downtowndougbrown.com · 11/04/2025

And the replacement works great! Alps Alpine SKHCBFA010, for anyone else who needs the exact replacement part. The button push force and color is an exact match.

010

Doug Brown @downtowndougbrown.com · 05/04/2025

My Mac Classic II’s reset button is corroded and doesn’t work. Thanks to the SE/30 reloaded BOM, I found it’s just a readily available Alps tact switch in a plastic carrier to make it right-angle. Yay!

130

Doug Brown @downtowndougbrown.com · 29/03/2025

Yay, I figured out how to exit out of the demo by looking at its MacroMind Director Lingo code. You press option-p to quit. Here's another screenshot. Unfortunately the store demo program hangs MAME but it works great in Basilisk II. Definitely going to share this on the Garden.

020

Doug Brown @downtowndougbrown.com · 27/03/2025

I promise I'm not trying to turn into "the guy who posts about nothing but Mac Performas on bsky", but it appears that I've accidentally stumbled upon a piece of Apple's store demo software. It helps me choose whether to buy a 410 or 466 and teaches me how to use a mouse. More stuff to preserve...

150

Doug Brown @downtowndougbrown.com · 25/03/2025

It's kind of fun looking at how random Mac UI elements evolved over time. One of the changes listed between System 7.1P5 and 7.1P6 was "Improved incorrect shut-down dialog." Seems like the language in the newer version was a little bit "nicer" about it.

This computer was not Shut Down properly the last time it was used. Next time, choose the Shut Down command from the Apple menu. Press the return key to continue.

This computer may not have been shut down properly the last time it was used. To turn off this computer, always choose Shut Down from the Apple menu. Press the Return key on the keyboard to continue.

010

Doug Brown @downtowndougbrown.com · 24/03/2025

Although it wasn't worth writing about, my crazy search for hard drives also led me to find the older caddy-loading Performa 550's original software bundle. I distinctly remember mine in the '90s having Monopoly too. This is earlier than the 7.1P6 restore CD that everyone uses.

181

Doug Brown @downtowndougbrown.com · 20/03/2025

I wonder how upset people in 1994 would have been if they realized Apple was leaving 3.6 MB of space on their 160 MB hard drive unused? And really, more like 6 MB considering the recovery partition was empty after restoring from CD.

010

Doug Brown @downtowndougbrown.com · 13/03/2025

I just realized that in the special Performa version of Apple HD SC Setup (7.2.2P) on the System 7.1P5 Utilities disk, Apple accidentally forgot to turn off debug symbols! So the function names are intact. Could be useful for anybody doing reverse engineering. Left: 7.2.2. Right: 7.2.2P.

010

Doug Brown @downtowndougbrown.com · 25/02/2025

This is the Utilities disk that came with my childhood Performa. Today I discovered it was acting up, and I was able to fix it! Ran an old hard drive magnet over it several times in a circle, then restored it from the original DC42 on the December 1993 dev CD. It works! Now…will the fix hold up?

120

Doug Brown @downtowndougbrown.com · 20/02/2025

Also, just to show this isn't a silly ResEdit hack, here's the readme that came with it...

010

Doug Brown @downtowndougbrown.com · 20/02/2025

I like to live dangerously. 7.5.4 is the system version that Apple released for a very short time and then pulled, replacing it with 7.5.5.

120

Doug Brown @downtowndougbrown.com · 12/02/2025

Found this local-ish to me, in great condition! The hard drive was reformatted in 1998, so it provides no extra knowledge of the recovery partition stuff. But…this looks exactly like the 550 I grew up with — the older caddy-loading model. Happy to have it!

140

Doug Brown @downtowndougbrown.com · 02/02/2025

Here's another sneak peek at the Performa 550's automatic OS recovery process. This is what you get when it boots up after the recovery.

010

Doug Brown @downtowndougbrown.com · 28/01/2025

So this happened today. Bet you've never seen this screen before. This is from a Performa 550. More details later...and of course software preservation!

140

Doug Brown @downtowndougbrown.com · 21/01/2025

Did you know that the Welcome to Macintosh screen is technically a system error dialog? It's also known as dsGreeting. The "ds" stands for deep shit. I'm not kidding...

000

Doug Brown @downtowndougbrown.com · 19/01/2025

Here's a sneak peek at some of the ROM hacking craziness I've been doing with the Mac Classic II that I recently bought. I've got an interesting story to tell, blog post about it hopefully coming in the next few days.

110

Doug Brown @downtowndougbrown.com · 08/01/2025

Thanks Adobe Reader, that was really insightful. 🙄 (It ended up being on sheet 3)

000

Doug Brown @downtowndougbrown.com · 06/01/2025

Oh yeah, this board from the mic also ended up with the same problem. I feel simultaneously like an idiot and also very proud of my repair job! The reason I needed the epoxy was because without it, I couldn’t plug the cables back in without moving the connectors and damaging all my work.

000

Doug Brown @downtowndougbrown.com · 06/01/2025

I’m almost embarrassed to share this because of my mistake. Bought this HyperX mic for cheap because it needed a new USB port. Easy, right? Well…the PCB turned out to be super fragile. These connectors ripped right off. But I fixed it!! It took 2 tries, but I fixed it! Needed epoxy to secure it all.

100