Howdy, everyone. After a three or so year hiatus from the hobby, and probably five from being really into it, I'm finally getting back into the retrocomputing hobby. The first item on my to-do list was to resurrect my 1991 Macintosh Classic, which has been the least reliable computer in my collection.
After getting the Classic back in 2020, the first thing I did was have both boards professionally recapped by other hobbyists. The logic board was recapped by a fellow 68kMLA user out in California, while the analog board was done by Amiga of Rochester. The machine worked well for a couple years, with some minor hiccups that were easily fixed, until May 2023 when it started exhibiting some real strange behavior. It would work sometimes before crashing with patterns and strange audio. Other times it refused to boot at all, just displaying a Sad Mac with code "0000000F 0000000D." I made sure everything, especially the memory expansion card, was snug. (I had experienced odd behavior previously from the card being loose and not making good contact in the slot.) Nothing made it stable and I began down the troubleshooting road.
First I checked the voltages, going off a pinout diagram of the molex plug for the power/video/sound cables to the analog board. Everything looked right: 5.04 volts on the 5-volt rail, 12.16 volts on the 12-volt rail. In hindsight I can't recall right off if those measurements were made under load with the logic board connected, but they looked good. Then, per the suggestion of many on here back then, I measured continuity of the reset and interrupt switches to make sure they weren't stuck closed. Both tested open when not pressed, closed when pressed. That didn't seem to be an issue either. Based on an online (non-official) schematic of the logic board, I hypothesized that the sound chip (UA5) could be the culprit. Upon closer inspection it appeared it could be as a couple legs were oxidized and didn't look too healthy.
I gave up due to a lack of equipment and skill... about the most "advanced" test gear I have is a rather basic digital multimeter, and my skillset reflects that. I sent the logic board to Amiga of Rochester for more advanced diagnostics and rework. He confirmed my suspicions that UA5 was behind it all. He removed the chip, cleaned it and the board, and soldered the chip back on. He recorded a test of the machine afterward and it fired right up and appeared to be stable.
After getting the board back, I plugged it in and everything was hunky-dory for a couple weeks. Then it started acting up again, though only intermittently. However the problem progressed to happen more often as time went on, and eventually the machine wouldn't boot at all except in rare cases ... and then it'd only stay up for a minute or two. The machine kept getting stuck in the same old "chime cycles" — continually rebooting and chiming. It doesn't seem to ever display a Sad Mac screen anymore. When it does boot into the OS, it will eventually display the interrupt dialog (as if the interrupt button had been pressed) then start going haywire. The machine became so unreliable that I shelved it and just kept using my SuperSE (an upgraded SE) and later added a Performa 6200CD — my first PowerPC Mac (that I owned) — to the collection.
That brings us to today. Just moved, so I have much more space to use and tinker on my old computers along with some renewed passion. The space has even allowed me to get video of the Classic, its issues, and a look inside — including myself rambling and looking like a fool on camera, even dropping the bucket screws and losing one altogether. (It was my first time working on a compact Mac since 2023.)
If you happen to have any clues as to what might be ailing my old Classic, it would be great to hear it. I might end up shipping the board off eventually to someone more equipped (probably back to Amiga of Rochester) for more probing and troubleshooting but would like to rule out anything simple that I might be overlooking. Any help would be greatly appreciated as always.
After getting the Classic back in 2020, the first thing I did was have both boards professionally recapped by other hobbyists. The logic board was recapped by a fellow 68kMLA user out in California, while the analog board was done by Amiga of Rochester. The machine worked well for a couple years, with some minor hiccups that were easily fixed, until May 2023 when it started exhibiting some real strange behavior. It would work sometimes before crashing with patterns and strange audio. Other times it refused to boot at all, just displaying a Sad Mac with code "0000000F 0000000D." I made sure everything, especially the memory expansion card, was snug. (I had experienced odd behavior previously from the card being loose and not making good contact in the slot.) Nothing made it stable and I began down the troubleshooting road.
First I checked the voltages, going off a pinout diagram of the molex plug for the power/video/sound cables to the analog board. Everything looked right: 5.04 volts on the 5-volt rail, 12.16 volts on the 12-volt rail. In hindsight I can't recall right off if those measurements were made under load with the logic board connected, but they looked good. Then, per the suggestion of many on here back then, I measured continuity of the reset and interrupt switches to make sure they weren't stuck closed. Both tested open when not pressed, closed when pressed. That didn't seem to be an issue either. Based on an online (non-official) schematic of the logic board, I hypothesized that the sound chip (UA5) could be the culprit. Upon closer inspection it appeared it could be as a couple legs were oxidized and didn't look too healthy.
I gave up due to a lack of equipment and skill... about the most "advanced" test gear I have is a rather basic digital multimeter, and my skillset reflects that. I sent the logic board to Amiga of Rochester for more advanced diagnostics and rework. He confirmed my suspicions that UA5 was behind it all. He removed the chip, cleaned it and the board, and soldered the chip back on. He recorded a test of the machine afterward and it fired right up and appeared to be stable.
After getting the board back, I plugged it in and everything was hunky-dory for a couple weeks. Then it started acting up again, though only intermittently. However the problem progressed to happen more often as time went on, and eventually the machine wouldn't boot at all except in rare cases ... and then it'd only stay up for a minute or two. The machine kept getting stuck in the same old "chime cycles" — continually rebooting and chiming. It doesn't seem to ever display a Sad Mac screen anymore. When it does boot into the OS, it will eventually display the interrupt dialog (as if the interrupt button had been pressed) then start going haywire. The machine became so unreliable that I shelved it and just kept using my SuperSE (an upgraded SE) and later added a Performa 6200CD — my first PowerPC Mac (that I owned) — to the collection.
That brings us to today. Just moved, so I have much more space to use and tinker on my old computers along with some renewed passion. The space has even allowed me to get video of the Classic, its issues, and a look inside — including myself rambling and looking like a fool on camera, even dropping the bucket screws and losing one altogether. (It was my first time working on a compact Mac since 2023.)
If you happen to have any clues as to what might be ailing my old Classic, it would be great to hear it. I might end up shipping the board off eventually to someone more equipped (probably back to Amiga of Rochester) for more probing and troubleshooting but would like to rule out anything simple that I might be overlooking. Any help would be greatly appreciated as always.