3.5" LCD screen scrambled (DX screen, NOAC/yobo project)

[Jish]

Hello; I've been lurking around this site for years now and have finally decided that I am going to make a NES (yobo/NOAC) handheld. I bought Ben's book a few yrs ago, but decided I wanted to go with something easier at first, like a NOAC. I'm decent enough at soldering and know a little about basic electronics (obviously not enough though )

I'm using a Yobo as my NOAC and a 3.5" TFT LCD screen from DX that was recommended somewhere else on this forum (specifically this one: http://www.dealextreme.com/details.dx/sku.14781" onclick="window.open(this.href);return false;).

So far, I have the LCD screen powered by 4 AA batteries in a "series" to make 6V. I have not ran power to the yobo board yet, still trying to figure that part out (I assume from what I have read I will use a 7805 regulator?).

My problem is the image on the screen is scrambled. I am not sure what I need to do from here to fix it?
Here is a screen with the scrambled image from Bubble Bobble, usually it just looks like a black screen with a green bar on top and bottom.

Here is the 4 AA batteries in series. Also showing the power to the LCD screen. Right now I just have the Audio and Video leads from the LCD directly connected to the yobo AV. The original wires went from top to bottom on the LCD white, yellow, black, red.


The LCD that I got from DX shows that it comes with more (like a manual and another power cable), but mine only came with the LCD and this cable: Which i assume is (Yellow: Video, White: Audio, Red: Power). Weird thing is that if I disconnect the audio lead the LCD will stop working completely?


Hope that all makes sense. Sorry if this has been answered already, I searched and found a few little things that might help but I can't figure this out. Any help is appreciated. Thanks.

[marshallh]

First, run the screen on 9 or 12 volts (The battery voltage may be sagging under load)

This particular screen seems to have had a revision since Life of Brian reviewed it. Mine doesn't work with most N64 games, it seems to have real issues with syncing.

First make sure you're giving the screen more voltage like I said above (just to be sure) then try it on another console.

[Jish]

Thanks for the quick response.

Ok, I first tried to switch the games (Ninja Gaiden) and it seems to work a little better...for the first few seconds, then it goes back to a scrambled feed. I then tried 6 AA batteries @ 9V serial, and then 8 AA batteries @ 12V serial (12.07V multimeter), but no real change. I have hooked it back up to a TV with all of the games I've tried thus far and it still works flawlessly. So the Yobo is good, I think the LCD is good, I must be missing something though? Haven't tried another console, I only have a 360 available at the time.


EDIT:
Wiring ground seems like it might make sense for Video (and Audio), although, the wires included did not have ground for the supplied RCA cable. Which leads me to believe it is not necessary on this board.

EDIT:
Well, I hooked the Audio/Video up to ground from the battery and it seems to work great!
Now I wonder how many batteries I actually need?:)

[c_mon]

4 rechargeable AAs will be enough for your project. The voltage should be 4.6 to 5.4. Just try; you'll be fine.

[hailrazer]

Oh yea, I found out that the video ground on these Hong Kong monitors have to be hooked up to the battery ground.

I wonder if that is the problem with the rolling screen on all the 3.5" screens ?