Uploaded October 2025 | Updated September 2026, 1 week ago
The Macintosh IIsi was launched as a lower-cost alternative in the Macintosh II series. To keep costs down, Apple used more electrolytic capacitors, and the surface-mount electrolytic capacitors from the early 90s are past their expected lifetime. In addition, despite the power supply being made by Sony, the capacitors in it are also known to leak (though I can't help think "cost tweaking" by Apple led Sony to use lower grade capacitors).
Of the four Mac IIsi computers that I own, one chimes and immediately death chimes. This is actually a good thing: this means that the CPU was able to read ROM code. This also means that the Diagnostic Mode is likely available. I'm hoping that Diagnostic Mode will lead unto a cause, and potentially a fix.
And if we finish with this board, we might try some of the others boards.
Will we get Diagnostic Mode running? Will it turn out to be a broken trace/via? Will we get the IIsi booting to Mac OS? You'll have to watch to find out!
NOTE: At 1:17:31, I mention "one thing you didn't see" and then start talking about soldering a jumper. The thing you don't see is a jumper wire shoved into the mini DIN connector on the back of the IIsi to connect RX+ to Ground. I do not know why this did not work to put the Modem port into RS-232 mode, but at least I eventually get a jumper wire to solder on the Burn-In connector.
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Table of Contents
0:00:00 Pre-Roll
0:02:39 Greetings and Announcements
0:03:59 Getting Straight to Business... IIsigh, there's no Wheel of Regrets™ tonight
0:04:27 Confirming IIsi Number 4 Still Sad Macs
0:05:23 The Parts I Bought for Accessing Diagnostic Mode
0:06:40 FTDI Serial Adapter #JustinTime Windows Driver Install
0:09:08 Checking the Serial Cable and Pinout
0:12:30 Checking the IIsi Burn-In Connector (J19) Pinout
0:21:25 Incorrect Attempts to Attach Serial Cable to Burn-In Connector
1:16:35 The Correct Wiring of a Serial Cable to the Burn-In Connector
1:19:33 Fighting with PuTTY
1:21:21 Running Diagnostic Mode on IIsi Number 4
1:52:57 Finding and Fixing the Broken Traces (Mistakes are Made)
2:40:15 There's Still a Problem (I Don't Discover My Soldering Mistake Tonight)
2:43:21 Foreshadowing
2:43:50 Closing Thoughts
2:52:14 Outro
Links for Following Along (Amazon links are not affiliate links):
DB9 Serial to 9 Bare Wire Cable: amazon.com/dp/B0FF25LPDB
FTDI-based USB to Serial Cable: amazon.com/dp/B006AA04K0
Bomarc Schematics for IIsi (J19 on PDF page 5): github.com/nickpunt/nubus-se30/blob/master/Schematics/bomarc/Macintosh%20IIsi%20Schematic%20(bomarc).pdf
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Ways to Support the Channel:
☕️ Tips or Support via Ko-fi: ko-fi.com/jdmcs
🈷️ Support me on Patreon: patreon.com/jdmcs
📦 Amazon Wishlist: jdmcs.net/wishlist
... or simply do the YouTube things: Like/Dislike, Comment, Subscribe, Enable Notifications, and participate in the Chat. These things help the channel, too!
**
Read Computerized Start™, my Official Blog: jdmcs.net/myblog
Follow me on Instagram: jdmcs.net/myinstagram
Follow me on Twitter: jdmcs.net/mytwitter
The Macintosh IIsi was launched as a lower-cost alternative in the Macintosh II series. To keep costs down, Apple used more electrolytic capacitors, and the surface-mount electrolytic capacitors from the early 90s are past their expected lifetime. In addition, despite the power supply being made by Sony, the capacitors in it are also known to leak (though I can't help think "cost tweaking" by Apple led Sony to use lower grade capacitors).
Of the four Mac IIsi computers that I own, one chimes and immediately death chimes. This is actually a good thing: this means that the CPU was able to read ROM code. This also means that the Diagnostic Mode is likely available. I'm hoping that Diagnostic Mode will lead unto a cause, and potentially a fix.
And if we finish with this board, we might try some of the others boards.
Will we get Diagnostic Mode running? Will it turn out to be a broken trace/via? Will we get the IIsi booting to Mac OS? You'll have to watch to find out!
NOTE: At 1:17:31, I mention "one thing you didn't see" and then start talking about soldering a jumper. The thing you don't see is a jumper wire shoved into the mini DIN connector on the back of the IIsi to connect RX+ to Ground. I do not know why this did not work to put the Modem port into RS-232 mode, but at least I eventually get a jumper wire to solder on the Burn-In connector.
*
Table of Contents
0:00:00 Pre-Roll
0:02:39 Greetings and Announcements
0:03:59 Getting Straight to Business... IIsigh, there's no Wheel of Regrets™ tonight
0:04:27 Confirming IIsi Number 4 Still Sad Macs
0:05:23 The Parts I Bought for Accessing Diagnostic Mode
0:06:40 FTDI Serial Adapter #JustinTime Windows Driver Install
0:09:08 Checking the Serial Cable and Pinout
0:12:30 Checking the IIsi Burn-In Connector (J19) Pinout
0:21:25 Incorrect Attempts to Attach Serial Cable to Burn-In Connector
1:16:35 The Correct Wiring of a Serial Cable to the Burn-In Connector
1:19:33 Fighting with PuTTY
1:21:21 Running Diagnostic Mode on IIsi Number 4
1:52:57 Finding and Fixing the Broken Traces (Mistakes are Made)
2:40:15 There's Still a Problem (I Don't Discover My Soldering Mistake Tonight)
2:43:21 Foreshadowing
2:43:50 Closing Thoughts
2:52:14 Outro
Links for Following Along (Amazon links are not affiliate links):
DB9 Serial to 9 Bare Wire Cable: amazon.com/dp/B0FF25LPDB
FTDI-based USB to Serial Cable: amazon.com/dp/B006AA04K0
Bomarc Schematics for IIsi (J19 on PDF page 5): github.com/nickpunt/nubus-se30/blob/master/Schematics/bomarc/Macintosh%20IIsi%20Schematic%20(bomarc).pdf
*
Ways to Support the Channel:
☕️ Tips or Support via Ko-fi: ko-fi.com/jdmcs
🈷️ Support me on Patreon: patreon.com/jdmcs
📦 Amazon Wishlist: jdmcs.net/wishlist
... or simply do the YouTube things: Like/Dislike, Comment, Subscribe, Enable Notifications, and participate in the Chat. These things help the channel, too!
**
Read Computerized Start™, my Official Blog: jdmcs.net/myblog
Follow me on Instagram: jdmcs.net/myinstagram
Follow me on Twitter: jdmcs.net/mytwitter
![The Apple ][ Plus Clone: The Desolation of Sockets... as I Attempt Repair (Computerized Start™ Live)](https://i.ytimg.com/vi/BkyfY4LIXzg/mqdefault.jpg "The Apple ][ Plus Clone: The Desolation of Sockets... as I Attempt Repair (Computerized Start™ Live)
Ive launched a merch shop: https://shop.jdmcs.com - use code JUSTINTIME for 5% off all Computerized Start™ merchandise through at least June 30th!
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I bought an Apple IIe Clone Motherboard on eBay (the place where I buy the things I later regret™) knowing full well it was an Apple ][ Plus clone motherboard and missing some chips. Yes, COMPUTER was jealous at first, but then COMPUTER realized I needed practice on a similar motherboard before I continue removing sockets, so were good...
Last time I worked on this board, I replaced enough capacitors to satisfy my concern that there wasnt enough capacitance on the board for proper operation. I was able to confirm the original 6502 was working by swapping it into my Apple ][ Plus. I also removed a few sockets that looked like they had too much solder. Still, the board powers up to garbage. I resigned to ponder the schematic.
Tonight, I am going to replace the rest of the capacitors, then I will commence The Desolation of Sockets. I have identified a few components that could prevent the CPU from running code, and I will be removing sockets for those components if they look questionable underneath. Well go from there.
Will I find issues under sockets? Will I get the board to do something by the end of the stream? Youll have to watch to find out!
*
Ways to Support the Channel:
☕️ Tips or Support via Ko-fi: https://ko-fi.com/jdmcs
🈷️ Support me on Patreon: https://www.patreon.com/jdmcs
📦 Amazon Wishlist: https://jdmcs.net/wishlist
... or simply do the YouTube things: Like/Dislike, Comment, Subscribe, Enable Notifications, and participate in the Chat. These things help the channel, too!
**
Read Computerized Start™, my Official Blog: https://jdmcs.net/myblog
Follow me on Instagram: https://jdmcs.net/myinstagram
Follow me on Twitter: https://jdmcs.net/mytwitter")
