Need advice on a PS1 VGA mod

Hello everyone!

I am going to install a VGA port on my PS1. It will output RGBHV, C-Sync, and +5V. The reason I am adding C-Sync to it is because I going to be making a custom VGA to SCART cable for a modded Dreamcast VGA box. It's going to be a while before I get a 15Khz-compatible VGA monitor so I figured I could use a cable I'm already going to make.

I am aware that most VGA monitors do not accept 15KHz RGBHV signals and 240p/480i. The H-Sync and V-Sync signals are going to be present for when I get a VGA monitor that accepts those signals and resolutions.

I found this guide online for getting the three sync signals but I wanted to check here to make sure it's correct. It is for a SCPH-7501, which is the PS1 model I have.

What parts will I need for this? Is it as simple as wiring the RGB signals and the sync signals to the VGA connector or will a need resistors and/or capacitors? What pin on the VGA connector should I wire C-Sync to? I was thinking of either wiring it to an unused pin on the VGA connector or just wiring C-Sync and H-Sync to a SPDT switch.

Money is tight right now so I can't afford to buy a PS1 SCART cable. Besides, I have dozens of parts lying around so I would like to use them for something.

Any help will be highly appreciated!

 

Can't help you there, but if you need a monitor, in a few months I will have an HP LP1965 monitor that I'll let go of for cheap. Also have a few others, just not sure what the KHZ are on them.

 

If they are modern, most likely 31KHz.

 

Oh. Never mind. One sec... I'll pull up the specs for the ones I'm not using.

 

OK, there are a couple of things that might cause issues - the first is that the standard levels for the sync signals on VGA are 5V TTL, and the PSX GPU is a 3.3V device. Having said that, 3.3V is a good logic "1" level for TTL, so the main possible issue is if the monitor has pullups on the inputs and they try and pull the sync lines > 3.3V. Second one is that the PSX has fixed sync polarity and some (generally older) VGA monitors used the sync polarity to indicate what resolution the display card was running in. Maybe this isn't an issue, since it sounds like you are going to be using a multisync type monitor anyway, and they directly measured the line and frame sync rates rather than using the polarity of the sync lines.

The pinouts on the page you linked to look correct to me - incidentally, those pads they are calling out as being a good place to pick the signals off from are the ones that were included in the design to make it easier to install the "Zenith sync fix" board that was needed to prevent the picture rolling on some Zenith TVs.

If you want CSync, you are probably better off putting it on the same pin as Hsync with a switch - there is no official composite sync pin on a VGA connector, and at various times all the pins have been used for something by somebody so trying to repurpose some other pin is could be risky.

 

Thank you for the info. I had no idea the sync signals needed 5V. I also had no idea there were issues with some Zenith TVs or a fix for it. I'll put a switch on the H-Sync pin then.

Any other things I should wire to the connector other than Red, Green, Blue, H-Sync, V-Sync, and C-Sync? I was thinking of putting +5V on the 5V pin for my custom VGA port to SCART plug cable. I could then use a 220ohm resistor on +5V in the cable end for pin 16.

 

I know it's not what you're asking, but i think is easier to find this



Even has a great review here: http://retrogaming.hazard-city.de/

 

Funny, this is something I was attempting not two weeks ago for the first time. I was able to get my VGA running on the menu screen, which as I've read runs at 480i, but when any game launches I get an error message. I feel like the problem is just that I don't have a proper monitor to display 240p. Those H/V-sync and C-sync locations seem to be right, I used them in my design. Although I have a SCPH-5501 console and there were no pads on the front so I traced them from the chip to some pads at the back. I did add some 220uf capacitors to the RGB signals which apparently should add some brightness, but I haven't seen a difference really. I noticed that on the schematic I pulled off of the repair manual the V and H sync are labeled as negative and have been reading that the polarity may have something to do with display resolution and also I had no idea about the 3.3v vs 5v thing either myself, so these could also be issues with my monitor if not just the fact that games run at 240p. I'll attach some pics of my mod, hope it helps at all or if anything I look forward to see what you've done with your own mod.

Orange is V-sync, and White/Orange is H-sync if I remember correctly, and the Orange/Blue/Green wires on the connector are my RGB signals. I actually broke the pad off the H-sync, so the pad used to be a little to the left of where I have it soldered now.

 

I knew the PS logo screen is 480i but I didn't know that the PS main menu was as well. Most games run at 240p/288p though. I'm going to add the caps on the VGA port so I won't have to put them in the cable.

Since you've done this mod, is the image quality better than RGBS via SCART/JP-21? I'm guessing it would be better since it uses separate sync signals but I was wondering if it is a noticeable difference. I'll give this mod a go once I get a VGA connector. Any other wires I need to solder other than RGB and the three sync signals?

 

As far as I know that's all you need. I actually did the VGA mod on my Dreamcast not too long ago and I believe it's in the same ballpark, just the RGB signals and Sync signals. Attached a pic of what that looked like to give you an idea. I did ground my pin 9 for this though, but I don't think that makes a difference, as apparently it's a +5v signal that only some monitors take and which could actually damage other monitors not prepared for that, as far as I've read. And of course ground pins 5-10, 9 being up for debate. I tried hooking up the PS1 with the resistors from a 5v source and the diodes to ground, but I noticed it didn't make a difference in picture quality either way, so I think it's safe to say you can ignore that part for this, then again I'm no expert.

I have no idea about the RGB scart picture vs this since I don't have a capable screen to look at that on, in theory RGBS should actually be a little better, but then again I really don't know.

Oh and note that the caps are oriented in this way: Board (+ -) VGA. so positive terminal to the board, and negative to the output port.

 

Ok, thank you for the info. I'll put a SPST On/Off switch on +5V to avoid any issues. I will only be using it for my custom VGA to SCART cable. I just hope a 220ohm resistor would enable RGB mode in my SCART to HDMI converter.

I figured RGBHV would be better than RGBS since it has separate sync signals. I'll have to compare it when I get this mod done.