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Troubleshooting a IIsi


Well-known member
Alright, here's what we got: A IIsi that won't show video. Have a real mac monitor, so we can take away all the hubub about getting a vga monitor to work.

Only shows a black screen. I know there's a system on it because I put the drive in my quadra. Everything with the hard disk is fine.

I know the memory is good because I swapped in my quadra's (700) memory. Still the black screen.

Can't be the PRAM battery, Cause I swapped that with the quadras and flashed the pram a couple of times.

Now I'm probably looking at a pretty serious hardware problem, I think, unless I'm missing something obvious. Any ideas?



Well-known member
It's been a long, long time, but my old Performa 600, even with vram maxxed out, was picky about what monitors it would drive; I recall my disappointment (and the Apple reseller's surprise) when it simply refused to run a bog-standard 15" Apple monitor, and I had to settle for a 14" screen for a few years. (This is back in the day when these things were newish and still pretty expensive, and I certainly did not have a spare $500 to drop on a nubus video card for the thing.)

A small (14") monitor on a IIsi should work, but in the absence of that ... does your monitor offer native 640x480 resolution? That would be one question to ask. You might also try cleaning & re-seating the system ram; since your video is running off of those ram chips, they may need some TLC before you get any further.



Well-known member
I used to be fascinated with the IIsi (hence my handle). I have every piece of information (just about) that you can have relating to these machines, from the pinouts of all the chips inside them to the locations of different things in the ROM. You name it, if it deals with a IIsi, I probably have it or can get it. I did some digging and sure enough, I have a document (which used to be easy to get and some of you have probably seen before) that details the video pinouts, signaling, blanking timing, etc of the RamBasedVideo graphics chip/interrupt controller in this box. Based on the description, you could easily play around with the video sense signals. PM me your email address and I'll send it to you. ;)