Forcing monitor detection without losing brightness

[yatzr]

I wasn't sure where to put this, but I figure groovymame users are gonna run into this more than anyone else.

So I ran into an issue with my groovymame setup where my video card (which was connected to a jpac) would not detect that a monitor was hooked up, and so it wouldn't output any video.  It'd actually output video during the bootup sequence, but once it got to windows, there'd be no video.  Then I'd have to restart it with it hooked up to a regular monitor to get it to work again.

A few people had mentioned that this can be worked around by hooking up 75ohm resistors from each r/g/b line to ground.  I went ahead and soldered this up on my jpac, and sure enough, it worked!  My video card would now always output video!  Unfortunately, though, the video was kinda dark, and even with the brightness turned up all the way, it was just disappointing.  So then I hooked up my resistors with a triple pole switch so that I can turn the resistors on and off.  Here's a picture of that setup


The switch worked okay, but it was a pain to remember to switch the resistors on when turning the cab on, and then have to turn them off again.  So then I went searching for a better solution.  Big props to mgb for pointing out this guy http://www.altronix.com/products/product.php?name=6030

So I ordered that and a couple little 12v dpdt relays (make sure to get the non-latching type!), and I now have a fully automatic solution.  The resistors are "on" for the first 30 seconds that the computer is powered on, and then they are "off" until I shut the computer off.

Again, make sure to get non-latching relays.  I learned this the hard way by accidentally ordering the wrong ones first.

It's hard to tell in the picture, but the stuff that isn't supposed to touch, isn't touching

I had an old computer case fan with a pc power supply connector, so I used that for connecting power.  As soon as it's powered on, the timer relay will wait anywhere from 1 second to 60 minutes before activating it.  I have it configured to wait 30 seconds.  So before it activates, the little relays will receive 12v and activate.  This will connect the resistors to ground while windows is booting up.  Then after 30 seconds, the timer activates, the little relays are cut off from the 12v, and the resistors are no longer connected to ground.  It probably seems like a lot of trouble, but I'm so excited to not have to open my cabinet for this anymore!

[mgb]

Great. Glad to see it worked out.

[Andypc]

I am using 75ohm resistors on my j-pac and got round this issue, by just increasing the screen volts very slightly. Worked perfectly until I had an unrelated issue with my chassis. I am now using a different chassis and am getting the issue shown in this thread. I think this may be caused by the j-pac signal?
http://forum.arcadecontrols.com/index.php/topic,141990.0.html

[Calamity]

Hi yatzr,

Thanks for sharing this. A very clever solution.

[capitaineflam25]

Hi,

Thanks for the tip !

I'm facing the same issue with my HD4850.
Is the problem related to the card model or the fact that the card is outputting signal through DVI and not VGA ?
I've observed that if i plug the CRT to the 2nd DVI output i can make make Windows 7 boot in 15khz but i'm not able to get 640x480@30i.

Regards.