Adding RGB+CSYNC input to screen (uses cxa1645m)

Hello,
I found this great forum, and wondered if anyone might be able to help me out. It's not console related really, but this chip seems to have a lot of attention here and i'm not sure whats wrong.

I have a 7" dvd screen that displays an RGB picture with CSYNC. It doesn't have an RGB input and i would like to add one... To see if it works first, i opened up the screen to find the "cxa1645m" chip. After reading up about it, i lifted the R,G and B input pins and soldered my input wires to them. I then found the CSYNC input pin and did the same to that. After connecting an RGB+CSYNC device with compatible res, the screen was all fuzzy. So i investigated more and found that the screen has a seperate CSYNC trace running to it, so the sync wasn't getting to the screen. I put my CSYNC wire here instead and now i have a picture, nice and sharp and perfect colours. Two problems though:

1. I have a solid black (not transparent) horizontal bar (about 1/2 inch thick) that moves slowly up the screen, and repeats.

2. There are feint grey diagonal lines that flicker over the screen.

I wondered with the expertise on this forum if anyone might have an idea about what is wrong, or what i could try to fix this problem?

Thanks,
James.

 

Sounds like some of your sync signal is bleeding away somewhere, double-check your connections.

You'll also need to ground your inputs from your device to suitable ground points on the display PCB. Any of the socket input ground points will usually suffice, and you might have to ground each RGB line separately (or just connect all the ground points up together instead).

Failing that, try adding capacitors or 75ohm resistors to the RGB/ sync lines, for example like >this<
If the picture becomes too dark when using capacitors then don't use them. Maybe try a 75ohm resistor on the CSync instead.

 

Thanks for your reply, i've had a go at some of the solutions today but haven't really made any progress.

I tried adding different capacitors in-line on the sync wire, but apart from nudging the image a bit, no change.

I then tried resistors in line and mostly had the same result.

Finally i tried grounding the sync wire through a 75ohm resistor, and no real difference. Although when the ground end of the resistor was scratched against a ground point it added some fuzzy hum bars. The bars were nothing like the problem i'm getting though (mine is a solid black bar moving up, and diagonal wide grey lines flickering).

Just out of curiosity i tried grounding one of the rgb lines in the same way, but this just seemed to reduce the colour (i.e took some of the red away when placed on the red line).

P.S. i noticed today when looking more closely that the top few lines of the picture are slightly skewed as well, a few pixels pushed to the left/right.

If you have anymore ideas it would be greatly appreciated.

Thanks,
James.

 

Hi again,
I've also noticed something weird this morning.

When you haven't got a navigation disc in the screen for a while and then you put one in, the unit goes through some reset/mode change process which is normal... BUT during the few moments when the unit "restarts/resets" ready for using the navigation disc... the picture im sending from my rgb input corrects itself! no lines, no moving black bar! but then a few seconds later it goes back to how it was.

Thanks,
James.

 

Hi, it's possible that your sync input is overlapping, hence the perfect RGB picture when the sync from the units' own video output is interrupted.

Trace through your connections again, and make sure the units' own sync/ RGB/ composite video output is completely disabled.

 

Progress! Looked again and the dvd player sends a seperate composite feed to the screen. Disconnected this and now the lines are gone. Just left with the few shifter pixels/slanted line at the top.

I've noticed that the whites and now really too bright, is this something to do with the sync line also?

Thanks,
James.

 

It might be the input is a bit too strong, have a play around with resistors and/or capacitors (on the CSync) again to see if there's any improvement. Also try different input sources to see how they compare.

It's all about trial 'n' error with these things, I'm sure you'll have it all figured out soon enough.