View Full Version : Mac IIfx no video/not booting

January 12th, 2012, 09:31 AM
Have had this Mac IIfx for awhile and decided to try and get it working. On the first try, it showed no signs of life. Replaced the PRAM batteryies and now I get the chime and hard drive spins up, but I get no video from it, no further activity. I have thoroughly inspected it and found no obvious problems. As i don't have the proper apple monitor for this, I am using a Mac video (DB 15) to VGA adapter. Do I need a special VGA monitor with this adapter? Is there any way to confirm that the video is working and perhaps the problem is my adapter/monitor? Thanks.

Al Kossow
January 12th, 2012, 10:51 AM
I am using a Mac video (DB 15) to VGA adapter

You need an adapter with switches to force the monitor sense code to something like 640 x 480 (Apple 13" Color) if you are using
older Nubus video cards that don't know about VGA sense codes.

January 12th, 2012, 12:19 PM
Does this schematic look right?


January 12th, 2012, 04:52 PM
Make sure the adapter is set for 640x480, many old Nubus cards that came with mac II's won't do anything bigger then that. The video card might be fixed frequency or needs a SOG (sink on green monitor) to work.

January 25th, 2012, 02:46 PM
Yeah, it might need the sync-on-green signal. If it's an Apple card, you can pretty much forget it being able to work with normal VGA monitors.

January 25th, 2012, 11:31 PM
Found the correct adapter, with 10 DIP switches to set sense codes, sync, etc. And it WORKS! I have scratched my head and screwed with this machine for many months now, so its excellent to see it working!

And it was a lucky hit - I have lots of old VGA monitors, but a unit that I pulled out the trash a few years ago is the only one that works with this thing!

Thanks for the tip.