After you disassemble the projector case, you can see the projector light, the passthrough display and the board that powers it.

You have 2 options:

Try to remove the connecting flex cable between the display and the board and replace it/repair it or clean the contacts on both ends. [I have tried this without success as the wires ripped off because they were aged]

Remove the display from the position (with or without removing the flex cable) and allow the projecting light to go through the lens directly - this way you obtain a big round red light: Mars on your wall!