CXA2075 Upgrade (CXA1145)
A very common RGB to Composite video chip inside many retro consoles like the Amigas and Sega consoles is the CXA1145.
This chip uses external delay line chips that often fail, leading to no video out, bad chroma delay causing bad colors, or other issues.
As the delay lines are hard/impossible to come by, a great replacement is the CXA2075. This IC is almost 100% pin compatible with the CXA1145 except it uses an internal circuit to delay the chroma and luma so does not require the external delay line components.
In order to swap the CXA1145 out for the CXA2075, all we have to do is remove the old CXA1145, replace it with the CXA2075, and do the following.
Lift up pins 8, 9, 15, 16, 17 and 18. All these pins are different.
Pins 8 and 9 are audio on CXA1145 and BF pulse output on CXA2075.
Pins 15 and 16 are the chroma and luma outputs. These won't want passing through the delay circuit on the PCB so want lifting in the air.
Pins 17 and 18 are chroma and luma inputs on the CXA1145, and YTRAP and No Connect on the CXA2075 so need wiring differently.
Ensure you lifted up pins 8 and 9 of the CXA2075.
These are not used (BF pulse monitor, and not connect).
Join the pads on the PCB where pins 8 and 9 are now empty, to join audio in and out together so audio continues to work on the board.
Making sure the YTRAP (pin 17) is lifted, solder a 3.32k (for NTSC) or 2.61k (for PAL) resistor from YTRAP (pin 17) to VCC1 (pin 12).
This enables the internal Trap which acts as the replacement for the external Band Pass Filter and Delay Line.
You can now use the floating pins Chroma Out (pin 15) and Luma Out (pin 16) to drive S-Video signals.
Use a 75R series resistor and capacitor if desired, to get the correct impedance.
