VGA to SCART cable problem with white banding on top of screen. (photos)

[WalkToFreedom]

Hi. The screen I am using is from a RCA TV 28DG170A but the tube is actually a Thomson TX807C / CS-N2I.

I'm using this screen in my MAME project. I wired up a cable from the inserted diagram. For the most part it looks great, but if you take a look at the photos there is some white banding at the top of the screen and I have no idea how it is caused, I thought I might have been a grounding issue as if I removed the ground the banding would disappear but brightness would go down and the colours would look dull. I have since stuck the tube into my cabinet with the hope that I will somehow solve the problem. I have tried it on another almost identical TV (same model but 29" flat screen) and I get the same result, so I'm thinking is there some problem with the cable itself? I also have the User manual for the TV which includes circuit diagrams if that helps. Would really love to solve this problem as apart from this everything else in my project is looking brilliant.

Thanks in advance. Matt

[fredster]

Did you try and modify your computer video settings? It looks like it works for the most part, but maybe your refresh rate is too low.  Can you tweak that?

[MonMotha]

Some SCART TVs require that the inputs be AC coupled using large coupling capacitors.  220uF bipolar rated 5V or higher is generally sufficient.

[WalkToFreedom]

Did you try and modify your computer video settings? It looks like it works for the most part, but maybe your refresh rate is too low.  Can you tweak that?

Hi. Thanks for your reply. I don't think the refresh rate is too low as that varies depending on the resolution set, I've tried using Soft15hz and an ArcadeVGA card still the same result.

[WalkToFreedom]

Some SCART TVs require that the inputs be AC coupled using large coupling capacitors.  220uF bipolar rated 5V or higher is generally sufficient.

Hi. Thanks for your reply. I have no idea what that means but I'm going to consult with one of my colleagues and get back to you. Thanks!

[WalkToFreedom]

Some SCART TVs require that the inputs be AC coupled using large coupling capacitors.  220uF bipolar rated 5V or higher is generally sufficient.

Hi. Still didn't really understand what he said something about is it on a sync signal or RGB signal but he thinks it's a problem with the sync. I also had another suggestion that this might fix the problem: http://members.optusnet.com.au/eviltim/scart.htm

[MonMotha]

You place a capacitor between the PC and the TV on each video (RGB) signal.

[WalkToFreedom]

Here is some updated info.

- I tried it with another PC (P4) using an AGP WinFast card using Soft-15khz and it produces the same result.

- The other PC I have is a AMD X2 with an ArcadeVGA PCIe card.

- The AGP version is slightly better (less banding, by maybe 10mm) than the PCIe version.

- I connected a PS1 with an official PS1 SCART cable to the TV and it works absolutely fine, crisp and clear right to the top of the screen.

- Have made another cable and still the same result.

Hopefully this will shed some light on the problem!

[WalkToFreedom]

You place a capacitor between the PC and the TV on each video (RGB) signal.

Hi. Thanks for your reply. Could you explain a bit more how this relates to the problem. Thanks!

[WalkToFreedom]

Good news citizens! The problem is fixed!

Many thanks to Tim and his super duper 'Dodgy Diode' circuit: http://members.optusnet.com.au/eviltim/scart.htm

Basically the problem was with joining the two sync wires together. I trawled the Internet and came across many diagrams that showed this is the way to do it. However, if you take a look at the link it shows the right way to create a combined sync.

Thanks to everyone for your input!

Now onto the Artwork!

Up, up and away!!!

[Paradroid]

Good news citizens! The problem is fixed!

Great! That must feel good...

[WalkToFreedom]

Good news citizens! The problem is fixed!

Great! That must feel good...

Soooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo gooooooooooooooooooooooooooooooooo!!!