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Another Macintosh IIsi Restoration

Byte Knight

Well-known member
Well, I vowed never to buy another IIsi after I paid big bucks for one back in college and my parents bought an LC III, which was 5 MHz faster than my IIsi, for $1000 cheaper less than a year later. But, a very-clean non-working IIsi came up on here for $50 and I was looking for a project. I figured it would be an easy fix with such a pristine-looking logic board, but as they say, looks can be deceiving!

IMG_0928.jpeg IMG_0932.jpeg

I started by recapping the power supply and logic board. After that, the fan and the disk drive would spin up but not the HD. In addition there was no video and only weak / garbled sound. Eventually I figured out that the 12V rail was bad between the external speaker amplification circuit and the internal HD power supply. It looks like a cap must've leaked on the 12V trace and messed it up. A bodge wire fixed that and then the stock 80MB hard drive spun right up!

IMG_5814.jpg IMG_5815.jpg

It turns out I was wrong about the video not working - I was testing it with a VGA LCD monitor and a Mac to VGA converter. I assumed it would work with my IIsi since it worked fine with my LC III. Boy was I wrong on that one after trying just about every DIP switch settings possible... Luckily Eric from BlueSCSI donated an Apple Color Plus 14" Display that works great, so a big thanks to Eric!

Next task was getting the sound to work. It had very weak / garbled sound coming from the speaker but normal sound through the headphone jack. After looking over the schematics and testing continuity between components, I found a broken trace in the sound circuit. After bodge wire #2, the sound was a little louder but still garbled.

IMG_5816.jpg IMG_5817.jpg

I had another IIsi logic board with working sound but other issues, so I just started swapping out components in the speaker amplification circuit figuring the issue was there. I swapped out an IC (TL0718) and a couple of transistors (Q10 and Q11) and the sound through the speaker now works! Here's the strange thing - I put the "bad" components back in the spare logic board and the sound still worked fine in that board too. So maybe I just had a bad connection there or something...

IMG_5818.jpg

I replaced the stock HD with a speedy ZuluSCSI and 3D printed a little tray for it. Note that the ZuluSCSI and SCSI2SD require HD power to work unlike with the LC III.

I also added a blinky HD activity light for the IIsi just by adding another wire between the LED and unused lead of the speaker / LED power leads.

IMG_5811.jpg

With everything now working properly, I thought I'd try to speed up the purposely-slowed-down IIsi (so as to not compete with the IIci), so I upgraded the oscillator to 50 Mhz and added a TechWorks PDS FPU/Ethernet card (from Herb's Stuff). After some tinkering around with the disk cache and IIsi-RAM-Muncher, I was able to get a Speedometer 3.06 score of 6.55 compared to 2.83 for the stock IIsi. Even with that impressive score increase, the IIsi is still very SLOW doing anything having to do with the internet. I guess that shouldn't be surprising given that it came out before the internet really took off...

IIsi_speed.jpg

Part of the challenge of working on the IIsi is that because of the soft power circuit, it's difficult to test the power supply without actually having it plugged into the logic board. Overall, I'm pleased with the way it turned out and I'm not nearly as bitter about the price difference with the LC III any more. It kinda looks like the next generation of the IIgs, which is my favorite computer. And I really like that you can power up the computer and monitor from the keyboard - I've missed that feature with my old Macs. Now off to do some BBS'ing!

IMG_5813.jpg Picture 1.jpg
 

imactheknife

Well-known member
Well, I vowed never to buy another IIsi after I paid big bucks for one back in college and my parents bought an LC III, which was 5 MHz faster than my IIsi, for $1000 cheaper less than a year later. But, a very-clean non-working IIsi came up on here for $50 and I was looking for a project. I figured it would be an easy fix with such a pristine-looking logic board, but as they say, looks can be deceiving!

View attachment 47211 View attachment 47212

I started by recapping the power supply and logic board. After that, the fan and the disk drive would spin up but not the HD. In addition there was no video and only weak / garbled sound. Eventually I figured out that the 12V rail was bad between the external speaker amplification circuit and the internal HD power supply. It looks like a cap must've leaked on the 12V trace and messed it up. A bodge wire fixed that and then the stock 80MB hard drive spun right up!

View attachment 47204 View attachment 47205

It turns out I was wrong about the video not working - I was testing it with a VGA LCD monitor and a Mac to VGA converter. I assumed it would work with my IIsi since it worked fine with my LC III. Boy was I wrong on that one after trying just about every DIP switch settings possible... Luckily Eric from BlueSCSI donated an Apple Color Plus 14" Display that works great, so a big thanks to Eric!

Next task was getting the sound to work. It had very weak / garbled sound coming from the speaker but normal sound through the headphone jack. After looking over the schematics and testing continuity between components, I found a broken trace in the sound circuit. After bodge wire #2, the sound was a little louder but still garbled.

View attachment 47206 View attachment 47207

I had another IIsi logic board with working sound but other issues, so I just started swapping out components in the speaker amplification circuit figuring the issue was there. I swapped out an IC (TL0718) and a couple of transistors (Q10 and Q11) and the sound through the speaker now works! Here's the strange thing - I put the "bad" components back in the spare logic board and the sound still worked fine in that board too. So maybe I just had a bad connection there or something...

View attachment 47213

I replaced the stock HD with a speedy ZuluSCSI and 3D printed a little tray for it. Note that the ZuluSCSI and SCSI2SD require HD power to work unlike with the LC III.

I also added a blinky HD activity light for the IIsi just by adding another wire between the LED and unused lead of the speaker / LED power leads.

View attachment 47216

With everything now working properly, I thought I'd try to speed up the purposely-slowed-down IIsi (so as to not compete with the IIci), so I upgraded the oscillator to 50 Mhz and added a TechWorks PDS FPU/Ethernet card (from Herb's Stuff). After some tinkering around with the disk cache and IIsi-RAM-Muncher, I was able to get a Speedometer 3.06 score of 6.55 compared to 2.83 for the stock IIsi. Even with that impressive score increase, the IIsi is still very SLOW doing anything having to do with the internet. I guess that shouldn't be surprising given that it came out before the internet really took off...

View attachment 47217

Part of the challenge of working on the IIsi is that because of the soft power circuit, it's difficult to test the power supply without actually having it plugged into the logic board. Overall, I'm pleased with the way it turned out and I'm not nearly as bitter about the price difference with the LC III any more. It kinda looks like the next generation of the IIgs, which is my favorite computer. And I really like that you can power up the computer and monitor from the keyboard - I've missed that feature with my old Macs. Now off to do some BBS'ing!

View attachment 47214 View attachment 47215
Awesome job!
 

Corgi

Well-known member
There's something like https://smile.amazon.com/dp/B07WWBFL6J but it's really expensive for what it is. I have a single key-sized plastic cover that I use to prevent my cats from powering up my Beige G3. Unfortunately, I don't know where I got it, it's probably more than 20 years old, and I can't find any suppliers of new ones anywhere online.
 

Byte Knight

Well-known member
There's something like https://smile.amazon.com/dp/B07WWBFL6J but it's really expensive for what it is. I have a single key-sized plastic cover that I use to prevent my cats from powering up my Beige G3. Unfortunately, I don't know where I got it, it's probably more than 20 years old, and I can't find any suppliers of new ones anywhere online.
Thanks for the link, but I don't wanna pay more for the keyboard cover than my keyboard! 🤑 The plastic cover sounds like a good project for the 3D printer...
 

LaPorta

Well-known member
This is pretty cool stuff. I have a IIsi I bought a while back and have yet to get to, I will have to reference this.
 

Byte Knight

Well-known member
This is pretty cool stuff. I have a IIsi I bought a while back and have yet to get to, I will have to reference this.
My biggest holdup was not having a proper monitor to test with since VGA converters will not work with the IIsi.
 

bibilit

Well-known member
You probably don’t have the good converter, never had an issue, but i agree the original monitor is better in most ways.
 

Byte Knight

Well-known member
You probably don’t have the good converter, never had an issue, but i agree the original monitor is better in most ways.
The converter works fine with my LC III. I think it's more dependent on the monitor's ability to sync at 66 MHz.
 

Byte Knight

Well-known member
I was able to find a DayStar IIsi cache adapter / PDS passthrough for my DayStar accelerator - now running at 50 MHz! It's getting a bit crowed in there with the Ethernet card...

IMG_5888.jpg IMG_5890.jpg

Here's the upgraded Speedometer score:

IIsiSpeed.jpg

The IIsi is much more usable online now!
 

mikes-macs

Well-known member
Nice work.
I have five Mac IIsi that need to be recapped and their power supply recapped which I'll never get to. Someone should take them off my hands and do the right thing with them.
 
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