View Full Version : Mac II RGB->VGA adapter pinout question

February 18th, 2011, 11:22 AM
I have a cheapy RGB->VGA style connector. It doesn't provide the right scan rates to my monitor, but does display a rolling picture. The horizontal frequency appears to be okay, but not the vertical. I am aware of the sense lines and have googled a bit but I'd like some independent verification here... If I read the chart right, I really want only pin 4 grounded (pins 4,7,and 10 are the sense pins), but currently I have 4 & 7 grounded. This doesn't work properly. Does anyone else use an adapter and can you check it for me?


February 18th, 2011, 02:33 PM
Looks like you have a sync problem, the sense pins generally just limit the available resolutions in the Monitors control panel. Three things come into play here

1. What mac model?
2. Does the adapter have dip switches?
3. What kind of monitor?

Early NuBus video cards used in Mac IIs tended to be sync-on-green. Alot of these adapters allowed you to set them between different sync sources. I know the Belkin Mac2VGA adapter let me independently select the sync type the computer output, yours maybe missing the sync wire entirely if its SoG which most monitors do not support. My adapter's dip switches for reference: http://www.belkin.com/support/download/files/F3H1381revised.pdf

February 18th, 2011, 06:16 PM
It's a Mac IIci with built in video, and the monitor is a Viewsonic 6. Hmm..I didn't think about the sync...I have another monitor that has a selectable sync source so maybe I'll have to give that one a shot.

EDIT: It's a Viewsonic 6

February 18th, 2011, 07:25 PM
Well, my other, fancier monitor works like a champ with the adapter with no modifications... so I guess I'm good!