I'm seeing a lot more automatic commercial espresso machines with kaput brain boxes. This presents 3 options; 1) replace the PC board ($400 - 800), 2) rebuild PC board ($200- 400), or 3) convert the machine over to semi-auto use.
#1 is very expensive
#2 is still not cheap
#3 involves a lot of work, but is often the best choice. I remove the flow-meter, PC board, and the push button dosing pad. I add a rocker pump switch, do a bit of rewiring to activate the group 3-way valve when the pump is off, and add an auto-fill circuit.
I'd like to avoid buying an auto-fill circuit box since they're $150 - 300 a pop. I've come up with this diagram of how to use a SSR in place of the auto-fill box. To do this I'll have to run one leg (neutral) of the 120 vac power through the auto-fill probe and to the input side of the SSR and feed the other leg (hot) of the wire directly to the SSR.
See the diagram for details. Any comments or suggestions are welcome!