Saturn weird image

[traian]

I've installed a region free bios and a switchless  50/60 mod (the one with pic from mmmonkey). For a few days everything was fine.

After that the problems begin.  On composite the image is black and white and very dark. in some places it's so dark you can't see anything. It's like it has sync issues. The game plays, thou.

I removed everything and the console is now in original state. Only VDP2 pin 79 is lifted and connected to vcc.

The motherboard is:

SEGA 1995

171-7006C Main

837-11613-01 JPN

837-11891-01 USA

I found a pal saturn schematic. I replaced the encoder and the cap after it on composite. No difference.

Meanwhile I got a rgb cable (form aliexpress). With sync on composite, the image is completely dark. Can't see anything. With c-sync, the image has color for a fraction of second. The colors are kind of weird, Sometimes the image is impossible to see.

PLL pin 1 and enconder pin 7 are connected to vcc.

Any help is appreciated.

[zyrobs]

If you use 50/60 switch on NTSC board, you'll get a 50Hz signal with the NTSC 3.57MHz colour carrier, which is a very uncommon setup that most TVs simply do not support.
On PAL consoles if you do the 50/60 switch, you get a 60Hz signal with PAL 4.43MHz colour, which is more commonly known as PAL-60, and is more commonly supported, so the problem does not happen in that case.

You'll need to get an RGB cable, and one that is specifically compatible with NTSC consoles, since they use a different pinout than PAL units.

[traian]

Thank you for your reply. I'm having problems in 60 and in 50 hz. And my tv supports ntsc in 50 hz. Like I said, it was working in the beginning. I remember that some time ago someone said on assemblergames that the code for the switchless mod it's not really ok. Like the code it's active low and the saturn is active high (or the other way around). Is it possible that this switchless mode damaged the vdp2? Or I'm just unlucky? here's the code (at the bottom of the page):

www.mmmonkey.co.uk/sega-saturn-region-free-bios/

Also, what can affect the video signal before the vdp2?

[zyrobs]

I don't know much about the switchless mod, because I've heard so many stories about it not working, and I simply find a physical switch more reliable... plus with the region free bios you only really need the 50/60 switch now. Hopefully it did not damage the VDP2. If you just switch pin 79 on occasion, it should be able to handle that without faults, but your mileage may vary.

The VDP2 generates the video signal, the only thing to affect it are the clocks coming from the PLL. But if your only problem is composite colour, then the issue is most likely either the wrong colour encoding selector input on the CXA1645 chip, or the TV not properly supporting NTSC 4.43. It's also possible that due to the mod the Saturn is not outputting exactly the 50Hz vertical sync, and this can also make the TV not recognize it (for ex. PAL60 on the Saturn is more like 59.2 Hz instead of standard NTSC 59.97Hz, and this can break some upscalers).

[traian]

The rgb cable, power supply , encoder have been tested on another ntsc console on the same tv.

Here's a video using rgb cable (sorry for quality)

www.youtube.com/watch?v=82IUxmOmA7Y

You will see the image fading, wrong colors, etc.

Again, the switcheless mod is removed, vdp2 pin 79 is connected to vcc.

EDIT: i've just replaced the ram at ic15 and ic16 and that made no difference.