Thats a stuck NMI button, or floating NMI.
Look at the NMI button traces. Check for shorts, or opens. Especially the pull-up resistor. R11 being missing may have something to do with this. your missing a few components in that area.
First, Elemenoh, You were absolutely right!!! I managed to get some 682 and 204 resisters, soldered them in (lost one since I suck at micro soldering) recapped the board, and plugged it in. It powered on and booted, but no sound. So I checked continuity and found a broken trace between R2 and Q1. No problem. I bodged it, plugged it in, and BONG!!! I was very happy!! Then I rebooted and again no sound??? So I powered down and turned it off and back on again (I T Crowd stile) and still no sound. I'm ashamed to say that it took me several hours to notice that there was a lot of white crud built up around the ram on the other side of the board. I sprayed it with IPA and scrubbed it with a q-tip (did the same around the sound chip just to be safe). Now it's back to its full functionality!!
Thanks to everyone who helped me. I'll try to post a picture of it set up and running when I get a chance.
Oh, one more question: How do I enter a 2020 date in System 7.5? I keep trying, but it always reverts to 1920? I don't seem to have this problem in 7.1 or 6.
I have been working on a Mac SE/30 restoration and it is exhibiting a strange problem where it can't boot from a SCSI hard drive. To start, I replaced all the electrolytic capacitors and cleaned the board with alcohol to get rid of any remaining electrolyte. After the re-cap the SE/30 boots from the floppy drive and it the SCSI drive also shows up and can be used.
However, if I try booting from the drive it hangs on the "Welcome to Macintosh" screen. Activity sounds continue from the SCSI drive continue even though it doesn't complete the boot process. I have also tried using a SCSi2SD with the same result.
From here I am guessing that I may have one or more bad traces from the cap leakage, or possibly a bad SCSI cable? Has anyone else resolved a similar issue?
Kinda have to agree. The design / style elements clearly share a lot of DNA, but the Color Classic is so elegant and refined, and the Performa 575 looks weirdly... mutated? Like a Color Classic that took a LOT of roids and skipped leg day for years...