Hey, i just wanted to share what fixed my amiga 600 (rev 1.5) rgb-output problem (red and green signals were missing) it was caused by leaked capacitors that harmed few transistors and resistors. I think blue signal was saved because it's some components are underside of motherboard.
exact part names:
2x SMD RESISTOR 1206: 33 kohm
2x SMD RESISTOR 1206: 1 kohm
2x MMBT3904 SMD