Ever wonder what happens when you install one 256 KB VRAM SIMM and one 512 KB VRAM SIMM in an LC 475? I found a spare 68-pin 512 KB video RAM module while sorting through a pile of 72-pin RAM and couldn’t resist trying it alongside one of the existing 256 KB SIMMs. They say you shouldn’t do it. They have a good reason. The display becomes a complete mess: lines everywhere, poor screen updates and mouse-pointer trails that refuse to disappear.

Interestingly, the machine did still produce a usable-enough display to demonstrate the failure. I wasn’t expecting it to work at all. In the video, the repeated lines made small text a nightmare to read, and even opening another window was needed to clear some of the mouse trails. Still, I could launch a game and watch it run through the mess.

Apple’s own specification explains the problem. The LC 475 supports VRAM as a matched pair: either two 256 KB modules for 512 KB total or two 512 KB modules for 1 MB total. One of each is outside the supported configuration. Science achieved.

I also installed the replacement power supply I ordered from the US a few weeks ago. TDK makes a lovely PSU. The switch feels very solid. This one carries a 1993 date code and I believed it may have come from an LC III, although the date code alone does not establish which Macintosh originally donated it. Whatever its history, it works beautifully and, unlike my old one, isn’t covered in rust. Kudos to whichever Macintosh donated the organs.

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