ADC port not working, G5, 10.4.11 OS


I have an old ACD 22 inch if I remember correctly. I use it in emergency with a G4. I was using it all the time but the blinking of the power light was annoying an on further research it needs a new something or other for lighting. That is neither here nor there as the monitor still works. A short wile late the ADC post on my G5 went out. Got a coupler but then eventually got another monitor and hooked it up to the DVI. 2 years later my DVI goes out. I replaced the video card and the DVI works fine but I just got my old ADC out and it is NOT working. I tested it again on my G4 and it works fine. Had a friend come over and look and he says its my motherboard. The connection must be fried...anyone have an opinion? I fix or am I just out of luck?

THX for any ideas..
If you had not tried the ADC with your replacement video card, then it's possible the ADC connection was never working on that replacement video card. It has to provide both video and power to the display through the single ADC cable.
The connection between the video card and the logic board may have some corrosion.
Have you tried reseating the video card?

I think that the best way to check is to try a different video card that has a known good ADC port.
If that doesn't make a difference, then, yes, the logic board is the most likely failure.
Of course, that only prevents you from using an ADC display on your G5 - so you could use another display for the DVI connection.