Jailbar Fix (Sega Mega Drive)
More commonly seen when doing CleanRGB mods or other RGB mods that give a clean output, you will notice vertical jailbars on some models of Mega Drive.
This is often more noticable on blue areas.
This is ultimately caused by the chroma clock signal (that goes into the CXA1145 chip for color timing), generated by the VDP, crossing over the RGB or Sync pins.
You could trace the signal out of the VDP to the CXA, and correctly re-route it to avoid traces.
- 315-5313 / 315-5313A Pin 50
- 315-5487 / 315-5660 / 315-5700 / 315-5708 Pin 131
- 315-5685 / 315-5786 Pin 103
- 315-5960 Pin 153
The general fix is to lift up the pin on the VDP, and cut the trace for good measure.
However, I find this doesn't work on many models. Instead, I will lift the RGB and Sync pins on the VDP (check schematics for pins), and solder the floating VDP pins to the CleanRGB then out to the AV port for super clean output.
For example on the 315-5313 those are pins 27 (R), 28 (G), 29 (B) and pin 42 (sync) on the left side of the chip.
This is the result then through a CleanRGB mod, SCART cable and using the lifting VDP RGB and S pins.
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