For those using the Homepin board here are a few faultfinding tips.
First, assume that the new board is working. It's easy to blame an unknown but we go to extraordinary lengths to ensure the board is 100% when it leaves the factory. The chances of it being faulty are very slim.
Plug the new board in and make sure the green LED lights showing that the beam across the playfield is working.
IGNORE all other things. Forget about any DMD displays, warnings etc. Just concentrate ONLY on the new board and getting the green LED to light. Do not bother with any of the machines self tests at this early stage.
If the green LED doesn't light, chances are high that either the optos (TX and/or RX) are shot or poorly aligned. Attend to them as required and check the soundness of all wiring and connectors between them and the new board.
Again, IGNORE everything else until you get this green LED illuminated. You are wasting your time looking anywhere else. The mist ball will never work until you get this long opto beam working correctly.
A very simple bench test for those who doubt the board is working:
Wire a TX LED to a plug for J2 and an RX Phototransistor to J1, then plug them into the new Homepin board directly. Apply 12V and the green LED will light. Using a steel ruler or similar you can break the light connection between the two LEDs to confirm. The RX and TX are marked clearly on the new board. You can even solder the TX and RX directly to the PCB on the solder side for a quick test.
Also be aware that there are many replacement parts out there (RX/TX) that have the leads reversed in the body. These parts work perfectly BUT must be connected the wrong way around. See my other thread on this issue.