MAME cabinet, adventures in video

With a working display finally installed, I started figuring out what to feed it with.

The graphics card I have installed in the system is a PCIE Club3D GeForce 6600 with 128Mb of memory. The Sony telly has SCART and the Geforce has a TV-out port that can do composite, s-video and YUV component. Out of these YUV component would be the best of course, but converting that to RGB component (used in SCART) would require a bit of active electronics in-between. There is a DIY-option for such a box available, but because of all work with this project as-is, I don’t feel like going that road for now.

So s-video or composite it is then! I chose the latter to start with as I didn’t have a s-video cable at hand. Ok-ish color picture on the telly, but once I got the Nvidia ForceWare drivers installed (version 266-something) the picture turned black&white. WTF?! Switching NTSC / PAL from the control panel didn’t seem to affect anything so I started looking the net for answers..

Seemingly I was not the only one with these problems as I found a number of solutions where people had “fixed” their s-video for color signal by short-circuiting the chroma and luma pins. Wonder why they didn’t stick with composite to boot with ;).. Eventually, I stumbled across this one post where someone had downgraded the ForceWare drivers to version 81.98. I performed the downgrade and what do you know, color in the picture! Not that switching NTSC/PAL seemed to work this way either, but color on-screen nonetheless.

TV signal output format selection in the Nvidia control panel.

After the color issue was sorted out, I bought a s-video cable. This gave sharper picture, but crappier overall quality in a way. The colors were much more “washed out” than the composite (f.ex. almost no yellow on the Energy Star logo displayed during bootup), as if though the saturation would be nearly zero despite the setting was more or less cranked up from the control panel. There’s also something going on between the chroma and luma that looks as if the two signals would be out of sync; a small amount of colorful ghosting/shadowing is visible on edges of fonts and window elements. The effect can be toned down slightly by increasing filtering from the driver settings, but the resulting picture is about as blurry as what I get with composite.. or maybe even worse.

Initial s-video output quality of my GeForce 6600. Shouldn't be too difficult to compare the difference between the desktop icons and the green video input overlay generated by the TV.

Ok so more searching it is then! This time I started also looking into PAL specs and eventually found a forum post where someone recommended testing 91.31 drivers. These have a ‘advanced timing’ page that allows you to muck around with the H/V timing values (front/back porch etc.). After install, I check these settings and it turns out that the GeForce is running 1024×768 60Hz VESA. Wonder what happened to the PAL?! :)

Advanced timing settings under the Nvidia control panel. These sure aren't the settings to run a PAL tv with..

The ‘Mode & Timing’ pulldown does have presets for 720×576 interlaced & progressive, but I verified their values against Tomi Engdahl’s video timing calculator just in case. No problems there, but the driver seems to modify some hand -input values when they’re applied/saved. Despite the new settings the ghosting was still there, but the picture quality improved a bit. Now the on-screen UI text elements are almost readable!

At this point, IF you’d want to analyze the problem further it’d be about time to whip out an oscilloscope and actually check what kind of crap the GeForce is feeding to the telly. As the settings seem to do very little, the only viable option would be to compare the outputted video signal against the PAL spec.. I, on the other hand, decided that it’s safe to declare the Nvidia soft/hardware flawed (at least, as far as PAL goes) and started looking into converters. Surely, the GeForce can do proper VGA, so maybe feeding that through some cheapo VGA to s-video converter box will outperform the plain TV-out. I’m currently waiting for my order to arrive but as this will still take a week or two, I’ll return to the topic after I’ve actually had the chance to test what I ordered.

Moving on to video connectivity then.. Because my plan is to use the cabinet for PS2 light gun games too (GunCon2 requires a CRT to work), I needed to install a SCART switcher for selecting the signal source. Since the PS2 can output RGB, I can at least get a superb picture from that source through SCART. At first I was thinking of making the switcher myself but giving it a second thought, I ended up buying this ITEC switcher from Clas Ohlson just to save a bit of time. Did it save time? Not really.

The crap Mr. Ohlson sells

You see, despite having SCART connectors it turned out the box wasn’t fully coupled; only audio, composite video and s-video were hooked up. I don’t know whether this could be actually considered a hoax, but since the switcher is (connector-wise) SCART-only you’d assume it to be fully coupled. But it wasn’t and discovering this sure made me feel very screwed.. Oh well, at least the switch toggled composite video and audio between the SCART connectors :).

Not much of a surprise that shortly after, I found myself modding the box to suit my needs.  Funniest thing is that the cable used on the switcher actually has plenty of unused wires. So the box could’ve been fully coupled, but seemingly ITEC chose to save some cents in manual labor costs by leaving them unconnected! After stripping the cable a bit, I had plenty of wires for additional connections. Inside the box, I disconnected all inputs from the female SCART connectors (pins 2, 6 and 20) and re-wired input 2 to use also RGB (connecting pins 5, 7, 9, 11 and 16). Input 1 remains composite/s-video -only as I didn’t have a switch big enough for routing all the signals. The switch used in the box is a double DPDT (4PDT?), one 2-pole pair for audio and the other for video.

The modded SCART switcher

As you can see, there’s a power cable that connects to the PC power supply. This supplies +12VDC to SCART pin 8 through a switch; when enabled, turning on the PC forces the telly to AV mode (SCART input).

The completed SCART splitter

Regarding the s-video “fix” I mentioned, something like this here is NOT HOW YOU FIX THE COLOR! S-video carries luma and chroma in separate wires to improve picture quality (less crosstalk between the two). Thus, if you connect the pins together like on the link above, you’ll get composite. Doing so, you could’ve saved yourself from all the hassle and gone with the yellow RCA connector to boot with.

As for the video out performance of GeForce, I’d definitely recommend steering clear of Nvidia hardware if PAL TV-out functionality is what you’re looking for. All the hassle is just not worth the time spent :). Not sure if NTSC is different though.. I’m also curious whether ATI has similar issues with outputting TV signals. I would probably test a ATI in the MAME cabinet if I had one available. The Matrox card I have on my DOS computer sure doesn’t have any issues.. but then again, it’s Matrox. Back when that card was released, you did at least get the functionality you paid for! :)

In case you stumbled across this article looking for clues whats up with the TV-out of your GeForce, I’ll leave you with a couple of apps worth testing. First, the Nvidia Bios Editor (NiBiTor) allows you to check the ROM settings on the card itself, this is good for verifying what the card thinks it’s outputting. Second, there’s a Windows registry entry that will restore the classic Nvidia control panel. This allows adjusting some additional video settings that are hidden in the newer control panel.

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  1. MAME cabinet, video one more time « My Diy Blog - 15/05/2011

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