The polishing machine's servovalve has two coils that controlled the tilt of the torque motor. When wired in parallel and properly wired in relation to their polarity, the coils produce enough force to fully stroke the valve. However, if one coil is open, the valve only has half the force stroking the torque motor. Therefore, the valve cannot open completely. This reduces the maximum flow capacity, which slows down the response time of the valve.

The fact that the polisher would work fine part of the time indicated that hydraulics was not the problem. I found that if the cable feeding the valve was moved to a certain position and held there, the system operated properly. Closer inspection of the cable, where it entered the connector, revealed a solder joint of one wire with a “cold joint.” This wire separated from the terminal when the cable was bent in one direction, causing loss of power to one of the servovalve's coils. Re-soldering the wire to the terminal solved the problem.