A few weeks back I saw a Macintosh Classic advertised for sale on a local site, it wasn't really a model that I wanted but it had a nice M0487 ADB keyboard and mouse which I did want and the price was good so I decided to go an have a look. While I was speaking to the seller I asked him if he had any other Mac stuff that he want to sell and he brought out a Macintosh Colour Classic with keyboard. The Colour Classic didn't work but it was in great condition so I made an offer on both machines and got them for a very good price.
On getting the machines home I tried to power up the Colour Classic but there was no activity, I tried all the recommended easy fixes like replacing the clock battery and ensuring the keyboard was properly plugged in. This model won't boot unless a keyboard is attached because the start button is on the keyboard. But nothing worked. On pulling out the logic board it struck me that it was very similar to an LC575 board that I'd picked up the week before. I got a non-functional LC575 the previous week for $20, I needed a SCSI hard drive and floppy drive for my SE/30 restoration (see posts in archive regarding the SE/30 and LC575 dis-assembly). So I put the LC575 board into the Colour Classic and it powered up! It wouldn't load the OS but it went to the start up screen and was clearly functioning. Quite a lucky coincidence that this board fit this machine and also considering both the Colour Classic and LC575 were non-functional but for different reasons. The LC575 most likely had a bad power board and the Color Classic had a bad logic board.
On doing some research on the Colour Classic I discovered that upgrading a Colour Classic with an LC575 board is called the "Colour Classic Mystic upgrade". You've got to like that. Thanks to some detailed information on the web about the Mystic upgrade, I was able to patch a version of system 7.5 to install on the upgraded machine. The issue with the OS is related to the screen resolution, the LC575 has a 640x480 resolution whereas the Colour Classic has 512x384. So you need to patch a version of Mac OS so it thinks it's installing the system on an LC575 with 512x384 resolution. There is a great website which goes into detail about the Mystic Colour Classic upgrade and they have a guide on how to patch the system for use on the Mystic upgraded machine:
The zip file below contains System 7.5 patched for the Mystic Colour Classic:
Before doing the install I needed to fix the floppy drive. The floppy was in a similar state to the one I extracted from my Macintosh SE/30, see my post about the Sony SuperDrive head spring fix.
The logic board from the LC575 is a drop in replacement for the Colour Classic but the rear connectors don't line up with the back plate from the Colour Classic. So I adapted the back plate from the LC575 to fit the Colour Classic. It fits well but I had to drill new holes to hold it on. I also bleached it with 40vol cream peroxide to get a better colour match. I was really pleased with the result. The left picture below shows the original Colour Classic back plate at the top and the LC575 back plate underneath (cut into two pieces). The second picture shows the LC575 back plate cut down to fit the Colour Classic. The third and fourth pictures show the finished back plate.
The 4.5v clock battery on the LC575 motherboard was long dead as you'd expect so I replaced it with an "AA" battery holder which takes three batteries. Each "AA" battery is 1.5v so this makes up the 4.5v required. It also allows for easy replacement of the batteries unlike the original unit. To finish off this machine I added a PDS ethernet card to allow for easy transfer of software via FTP. The image below shows the LC575 logic board with "AA" battery holder and PDS ethernet card.