RGB cable quality/interference
Apr 19, 2015 3:33:28 GMT
Post by zyrobs on Apr 19, 2015 3:33:28 GMT
Okay, I tested a couple of different setups to check when the problem happens and when does it not.
Just to be clear, the problem in question is a visual anomaly on model 2 Saturns that use motherboards between version VA6 and VA9. The anomalies include a constant bend at the top row of the image, and smaller, minor bends appearing on random lines anywhere else. The random line problem is worse when the CD Drive is loading or playing music, and even more worse when the CD Drive is seeking to another location on the disc.
All tests were run using the RGB Scart cables purchased from ebay seller thefoo83, since these work on all Saturns, both NTSC and PAL. The official Sega-made RGB Scart cables only work (properly) on PAL units due to a pinout difference on the console a/v connector between NTSC and PAL units.
This cable is wired to use composite video as per the SCART specification.
First, on my plasma TV, a Panasonic TX-P42G10E:
- VA7 PAL unit: the problem exists and is very easy to spot, the entire screen has random bending running around on it.
- VA9 NTSC unit: the problem exists but it was fainter - harder to spot, harder to notice during games but it was definitely still there.
Just in case it is the power supply causing the problem, I put the 220v power supply into the NTSC unit, but it made zero difference on the video output.
Then I checked a CRT (some noname display, BEKO or something). The problem was still there, but it was so hard to spot you wouldn't ever notice it unless you looked for it. But this was not because CRTs handle the signal different. It was a combination of things:
- this was a low end TV, while my Plasma is a high-end one,
- CRTs displaying pixels differently than modern digital displays (this one used in-line shadow mask),
- phosphor afterglow,
- lack of calibration: the picture was not a proper square to begin with,
- it also had random lines bending, also regardless of the console,
- this TV is just much smaller! My plasma has a display almost three times the size, which makes visual anomalies easier to spot than on this old CRT.
I hooked up two different model 1 Saturns (a VA0 PAL and a VA3 PAL), and they didn't look much better - the permanent bend on the top was gone as expected, but it was extremely difficult to tell, I had to check the corner from 20cm away, which is not how you would usually watch TV. Also tried this using the official cables which are slightly higher quality: no difference whatsoever, and I was trying very hard to spot anything.
Finally, I hooked up the VA9 NTSC unit to my projector (SONY VPL-CS4), which *requires* Composite Sync to work with 15khz RGB input. Composite video is not usable for RGB input, only composite sync a.k.a. "raw sync".
For this, I used a SCART cable that came with PAL units. On PAL Saturns, the C-Sync output pin was changed to output 9V DC instead, as it was required for the SCART standard for auto switching. So by using this cable in a NTSC unit, I could just tap pin 8 of the SCART connector; this would be a 9V signal on a PAL unit, but C-Sync because I was using a NTSC unit.
I had RGB and C-Sync aka raw sync used for a connection, using the highest quality official SCART cable, hooked up to a VA9 NTSC unit. The result? No difference. The bending on the top right corner is there, and I could see the bent lines running around as well, when the CD Drive was seeking tracks. In fact it was even easier to spot then on my plasma screen, due to the fact that I was projecting a 2 meter 4:3 screen versus the 42 inch (~106cm) 16:9 display on my plasma tv (when set to 4:3, the picture was even smaller on the plasma). It also helped that the projector did nearly no image processing, and due to its native resolution of 800x600 (almost exactly the same as the consoles output), it also produced a much sharper image.
Also checked using composite video on my plasma and on the projector, and the artifacts were there using both.
Conclusion: this is definitely a hardware problem in the consoles. For some reason, it is also way more sever than on NTSC units. Cable type will not improve on the problem, other than poorer cables possibly introducing other issues. Composite, RGB, RGB + raw sync, all of them had the issue equally. VA0 to VA5 units don't seem to have this problem (I specifically checked a VA0 and a VA3 right now, but in the past I've also used VA1, VA2 and VA4 units, and none of them had the problem either).
I think this issue went unnoticed simply because on a typical CRT, you just can't notice it. But modern displays are much higher quality, which emphasizes the problem greatly. I wonder how visible this problem would be on a high quality CRT, like a properly calibrated Trinitron studio display - likely more visible than on the CRT set I used.
Just to be clear, the problem in question is a visual anomaly on model 2 Saturns that use motherboards between version VA6 and VA9. The anomalies include a constant bend at the top row of the image, and smaller, minor bends appearing on random lines anywhere else. The random line problem is worse when the CD Drive is loading or playing music, and even more worse when the CD Drive is seeking to another location on the disc.
All tests were run using the RGB Scart cables purchased from ebay seller thefoo83, since these work on all Saturns, both NTSC and PAL. The official Sega-made RGB Scart cables only work (properly) on PAL units due to a pinout difference on the console a/v connector between NTSC and PAL units.
This cable is wired to use composite video as per the SCART specification.
First, on my plasma TV, a Panasonic TX-P42G10E:
- VA7 PAL unit: the problem exists and is very easy to spot, the entire screen has random bending running around on it.
- VA9 NTSC unit: the problem exists but it was fainter - harder to spot, harder to notice during games but it was definitely still there.
Just in case it is the power supply causing the problem, I put the 220v power supply into the NTSC unit, but it made zero difference on the video output.
Then I checked a CRT (some noname display, BEKO or something). The problem was still there, but it was so hard to spot you wouldn't ever notice it unless you looked for it. But this was not because CRTs handle the signal different. It was a combination of things:
- this was a low end TV, while my Plasma is a high-end one,
- CRTs displaying pixels differently than modern digital displays (this one used in-line shadow mask),
- phosphor afterglow,
- lack of calibration: the picture was not a proper square to begin with,
- it also had random lines bending, also regardless of the console,
- this TV is just much smaller! My plasma has a display almost three times the size, which makes visual anomalies easier to spot than on this old CRT.
I hooked up two different model 1 Saturns (a VA0 PAL and a VA3 PAL), and they didn't look much better - the permanent bend on the top was gone as expected, but it was extremely difficult to tell, I had to check the corner from 20cm away, which is not how you would usually watch TV. Also tried this using the official cables which are slightly higher quality: no difference whatsoever, and I was trying very hard to spot anything.
Finally, I hooked up the VA9 NTSC unit to my projector (SONY VPL-CS4), which *requires* Composite Sync to work with 15khz RGB input. Composite video is not usable for RGB input, only composite sync a.k.a. "raw sync".
For this, I used a SCART cable that came with PAL units. On PAL Saturns, the C-Sync output pin was changed to output 9V DC instead, as it was required for the SCART standard for auto switching. So by using this cable in a NTSC unit, I could just tap pin 8 of the SCART connector; this would be a 9V signal on a PAL unit, but C-Sync because I was using a NTSC unit.
I had RGB and C-Sync aka raw sync used for a connection, using the highest quality official SCART cable, hooked up to a VA9 NTSC unit. The result? No difference. The bending on the top right corner is there, and I could see the bent lines running around as well, when the CD Drive was seeking tracks. In fact it was even easier to spot then on my plasma screen, due to the fact that I was projecting a 2 meter 4:3 screen versus the 42 inch (~106cm) 16:9 display on my plasma tv (when set to 4:3, the picture was even smaller on the plasma). It also helped that the projector did nearly no image processing, and due to its native resolution of 800x600 (almost exactly the same as the consoles output), it also produced a much sharper image.
Also checked using composite video on my plasma and on the projector, and the artifacts were there using both.
Conclusion: this is definitely a hardware problem in the consoles. For some reason, it is also way more sever than on NTSC units. Cable type will not improve on the problem, other than poorer cables possibly introducing other issues. Composite, RGB, RGB + raw sync, all of them had the issue equally. VA0 to VA5 units don't seem to have this problem (I specifically checked a VA0 and a VA3 right now, but in the past I've also used VA1, VA2 and VA4 units, and none of them had the problem either).
I think this issue went unnoticed simply because on a typical CRT, you just can't notice it. But modern displays are much higher quality, which emphasizes the problem greatly. I wonder how visible this problem would be on a high quality CRT, like a properly calibrated Trinitron studio display - likely more visible than on the CRT set I used.