Mac II Video glitch

[blturner]

This is crazy. Same computer, disk, memory size, video card, slot D, monitor adapter, and monitor.

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Different results

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The only known difference is in your parameter RAM. You have a couple of bits set in byte 11 and somehow you've got 32-bit memory set on a 32-bit dirty computer. I assume you have the special memory software (Mode 32, Optima, RAM Doubler, Maxima, Virtual, etc) installed in your System 7 image. (Aside: I set my highlight to invert and I have the same undocumented bit set in byte 1.)

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Can you pull the batteries from your IIx to allow parameter RAM to clear out. Then reinstall the batteries and boot directly to 6.0.8 (without first allowing it to boot to System 7.x). That should clear the bits that differ between us.

- David

Well, at least this makes me feel less crazy!

I pulled the batteries, reinstalled and booted into the disk image you provided: glitch remains.

I jump started it with no batteries installed: glitch remains.

I attempted to manually reset the PRAM from software (opt+cmd+shift open control panel) and restart: glitch remains.

I have previously installed MODE32, but not on the latest 7.1 disk. I last ran a clean install of 7.1 for Mac IIx only, not the universal install. It clearly seems like something is wrong with the PRAM settings, but how to fix it. I will note, I have at least one other board that exhibits the same video issue, I’ll pull it out tonight and verify.

 

[David Cook]

Have you tried running MacTest Pro? It has tests for the video card as well as the computer itself.

I usually click the Deselect All button followed by checking the video card, logic board, and ram tests.

 

[David Cook]

Last night I went through the Macintosh ROM source code to see if there were bug fixes related to this. While there are plenty of fixes related to inverted text, I didn't find an exact match. In any case, the patches were applied before System 6.0.8.

What I did discover was that Apple routinely overrode the driver on their video cards during system startup. That is, rather than issue ROM upgrades to the cards in the field ($$$), they just allow the card to start up from ROM and then close the ROM driver and replace it on-the-fly with a RAM based driver.

 

[blturner]

Have you tried running MacTest Pro? It has tests for the video card as well as the computer itself.

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I usually click the Deselect All button followed by checking the video card, logic board, and ram tests.

I ran the video and logic board tests a few times and everything passed. I also got out one of the other IIx boards and it does not exhibit the same issue like I remembered, so that at least isolates the logic board as the culprit.