I bought this system in a lot of faulty pcbs.
Game was booting but it had no sync and the graphic was all corrupted.
The OSC 21.477mhz was giving out around 12mhz
After changing it, the game was back to life but it was missing the blue component
Looking at the schematics , I could confirm that the RP004 video chip was giving good signal on the BLUE signal pin, therefore I started
to check the LM324 OP AMPS involved in the DAC circuit.
The output of the LM324 for the BLUE component was dead therefore I proceeded to change it but the game was not fixed yet despite now having a good signal
By turning the blue pot I could see briefly some “sparks” of blue ,therefore confirming that the blue component
was working again.
In the end it turned out that the blue pot had some cold joints on the ceramic base.
I reflowed the solder and the game was 100% fixed