Why would zones 4-12 stop working? Hunter Pro-C controller w/ one black expansion gives 6 zones. 1-3 worked, 4-6 show blinking sprinkler icon but no water/sound. On right side, moved zone 6 to 1 and can start watering manually. Multimeter measured common white terminal to 1-6 when each was blinking, got 25VAC on 1-3, nothing on 4-6. Bought new PLC-300 expansion module but no change. Replaced prior module in zone 4-6 slot so it would recognize the new one in 7-9 then 10-12 none of which have ever been used. When manually starting those zones in turn, measured no VAC. Slide module lock bar up to off, disconnected zone 1-6 wires and measured resistance, IIRC about 27 Ohms each. On left side I measured output of transformer and got 25VAC across the 24V terminals and some others from ground (Green) to REM/SEN wires. Rain sensor bypassed electronically and by manual switch. Any more troubleshooting ideas?