vga issues

[mancio]

Hello. I'm burning my neurons on a video signal issue. I bought a Pandora's box 3 vga HD. This is a plug and play card to play old arcade games. It can autoswitch between 800x600 and 640x480 signal. It is an embedded system with the sd and software inside (emulator + roms). Unfortunately the code is crypt and I'm unable to reverse engineering that. I tried to plug it to two old monitors with only vga plugs and other two with also dvi plug. I noticed that in the older it works fine, instead in the newer doesn't. One of them shutdown and led blink and the other monitor turns on and off repetitively. I check the pandora's box vga pinout. It use only rgb, v and h sync, and gnd pins. It doesn't use ID0,1,2 and 9 pin for data (ddc) and memory power. I suppose that newer monitors want establish a data dialog with the source board. I don't know how technically the software of the board can decide to switch from 800x600 to 640x480 without any feedback from the monitor. In fact seem that in newer monitor the board switch to lower resolution. If I plug a new monitor (not working) and after an older one, it switch on with 640x480 resolution. I used a signal scaler able to change resolution and I have the same issues. I check also the vga pins frequency. I supposed that the v and h frequency is some hertz different from the correct one. I check also the chips datasheets to find is an electrolytic capacitor should be changed for a ceramic one. I think these last two things are ok, because I saw that when I try to use one of the two new monitor it works properly by using a trick: when I find blinking led issues I connect the monitor to my laptop and it works; I set the ext monitor as 800x600 @ 40 hz (still working); then I reconnect it to pandora's box and it works fine. After all my studies I suppose that I should find the way to force the monitor and the pandora's box to 800x600. How to do it hardware side?..... ok someone should tell me:”just use an old monitor”... but I would like to know how monitors works and I would use a new monitor lighter then older (I have to fit it inside a cabinet on a wood panel)

[lilshawn]

some of these Chinese made XXX-in-1 boards often output a weird resolution refresh rate that isn't 100% compatible with all monitors. I don't know if they use a different refresh rate there or what.

I have a pile of 60-in-1 boards that don't work with newer Lenovo branded thinkvision monitors (image is way off screen and can't be moved over enough) but work okay with older IBM branded thinkvision monitors. (perfectly centred.) functionally the monitors are identical but the firmware in the new monitors don't like it.

not sure there is much you can do but try different monitors.

[obcd]

If only RGB and sync's are connected, the board can't know the supported resolutions of the monitor.
I doubt it will switch from 640 x 480 to 800 x 600 in such a case. There are different versions of the pandora board.
Some only support VGA while others still support 15khz RGB on the jamma connector.
Maybe some have a resolution of 800x600 on the vga connector while others use 640x480.
It looks like your board is using the 640x480 resolution, and likely modern lcd's don't like it anymore.
I finally tested it with my pc, and even it's bios screen is using an 800x600 resolution.
Pretty much all xp "system windows" don't display properly anymore on a 640x480 resolution (they don't fit vertically in 480 pixels),
so monitors might not support it anymore.
No idea why your monitor produces a picture after it was connected to the laptop first. So far, all my monitors I checked still support 640x480. An easy way to test is by using something like dosbox in full screen mode. The monitor OSD clearly shows 640x480x60 when I run that. Do you have prove the box run's 640x480 on some monitors and 800x600 on others?