Quoted from LongJohns:
I am working on a project Future Spa and have a question with regards to the driver board J3 connector (right most one on the top).
According to the wiring diagram there should be a white-brown wire at pin 10 of J3. On the solenoid driver board J3 pin 10 goes to the "-" (negative) lead of capacitor C23. Is there any wire sitting in location pin 10 of the J3 connector housing?
Sounds like someone's bodged the connection up onto pin 1 instead of pin 10 for whatever reason. If the negative lead of C23 is floating, the 5 volt regulator will not be able to provide a stable +5V supply.
You should do the ground mods on the solenoid driver board - one of them is to connect the "-" (negative) lead of capacitor C23 to the main ground trace on the SDB for better redundancy.