The resistor value (1500 Ohm) has been chosen as the best value according to our tests.
If the value is less than 1000ohm the pstwo will stay in a permanent reset state and not even the red led
will turn on.
On the other end if the value is higher than 3300 ohms the pic will not be able to turn off the pstwo when
needed. This has been tested on several machines with consistent behaviour.
However there might be other board revisions which might behave in a different way (maybe because of a
different reset controller IC used).
So if you experience problems with the 1500 Ohm resistor, you can probably safely increase it to 2000/2200
ohms. Please, only experiment with different values if you understand what has been said (or if you don't
care about running your pstwo without being sure that the coils protection is working).