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Did you use the same disk image on the II as the IIci? Just to rule out a software / OS issue. Can you describe this further? Is this a ROMinator on the IIx? The fact that the glitch doesn't show on the IIci is very interesting. It rules out the card, adapter, and LCD -- which is progress.

That's crazy. Definitely related to highlight. What system version?

Try changing the highlight color in the Color control panel (?) to something like yellow.

And, it is only scrambling inverted text. That's a clue. Have you tried booting with extensions disabled?

Very interesting. It isn't the LCD. 1. Does it happen every single time in 256 mode? 2. Is the scrambled text always scrambled the exact same way or does it look randomly scrambled differently each time?

As everyone has mentioned so far, adding VRAM generally increases the maximum number of colors and resolution only. However, on accelerated NuBus/PCI/AGP cards, adding VRAM can speed up graphics. For example, the Apple 8*24 GC card can vastly speed up offscreen graphics with additional VRAM...

Tip for English listeners: When I played this video embedded in the TinkerDifferent page, it did not translate the audio. If you open it directly into YouTube, then it will.

Good catch! Not nickpicking at all. I put my notes up online to save trouble for other people. If someone plugs something into that internal connector then they will be on the same "slow" bus as the external connector and can have ID conflicts.

Hmm. I saw a couple of posts from people claiming they made a 4MB PCB layout, but I don't actually see the layouts themselves posted online. If I run across anything I'll let you know.

I recently picked up an 8600/300. I ran across a couple of interesting tidbits while playing with the computer. This is the enhanced model of the 8600 (Kansas motherboard) and stock 604ev @ 300 MHz CPU. For my tests, I'm using System 8.1 with the default extensions. RAM The computer came with...

If this is a 5120, it is a common issue that powering up sound (for the chime) introduces electrical noise into the 5V line and scrambles the CPU, resulting in sad mac. Connect a bodge wire to the sound power signal as shown below. If your Mac boots reliably, you can just leave this workaround...

Is this a 5120? If so, try adding a temporary bodge wire as shown in purple. There seems to be an electrical noise issue in many 5120 Portables when the sound circuit turns on. It causes the CPU to scramble. The above bodge just keeps the sound circuit on all the time. It is a workaround...

Let me know if you run into anything I can help with. Definitely double check for incompatible memory and make sure the board isn't shorted somewhere.

REPLACEMENT PARTS If priced reasonably, I will pick up battery bombed boards to repair other machines. In this case, the missing CPU and FPU were replaced with ones from a battery bombed board. The tops are ugly but the chips are solid. Replacement/repair summary: 1. New speaker 2. New ROM...

RUST REMOVAL The metal shield on the inside of the case was in horrible shape. The speaker is broken (open circuit). In the past, I've dunked an entire case in Evapo-Rust. https://amzn.to/4sJGM1V However, because I didn't want to remove or stain the weird IIfx label on the front of the...

ROM TROUBLE The seller did not include a ROM with this machine. Whoever removed it (and the CPU/FPU) is a jerk. I prefer the original ROM as it performs the complete RAM test on these finicky RAM slots. Additionally, only the original ROM will pass the MacTest Pro and Home editions of Apple's...

RAM TROUBLE Whenever I am repairing a board, I use known-good parts in everything that is removable. In this case, that includes swapping out the RAM and installing an original IIfx ROM. This approach reduces the number of variables I need to consider when the board isn't working. Earlier, I...

A seller offered this IIfx parts machine on eBay for $200. The seller was completely honest in the listing -- so all problems I describe in this post were risks I assumed. In the eBay image below, you can spot rust, missing CPU/FPU/ROM, and three RAM simms that differ from their mates. Rust on...

Here you go

Also noteworthy, the IIvx using a different system enabler than the Performa 600. Make sure you have both enabler 001 and enabler 304. https://www.macintoshrepository.org/505-macintosh-system-enablers So, if the cache is being enabled in that code (likely), it is critical that the System...