Disconnecting the Parallel Port Cable disables the drivers but enables high power circuit. This is a good time to make adjustments to the trim pots.
Motor Phase Currents
There is a 0.1 Ohm resister used for current sensing. Adjusting the trim pot sets the reference voltage. For each step motor there is a current adjusting trim pot. Near each trim pot is a test point pad that the current reference voltage can be read with a meter. The meter needs to be reference to ground, which is found at TB1-15 on the PWB.
When the voltage reads 0.100, the motor phase current is 1.0 Ampere. When the voltage reads 0.200 the motor phase current is 2.0 Amperes.
Turning the trim pot screw clockwise increases the motor current. A full revolution changes the current by 0.20 Ampere. By default the motor currents are set to 2.0 Amperes.
Chop Clock Frequency
There is a trim pot marked CHOP CLOCK FREQ, next to U5 for adjusting the Chop Clock Frequency. The frequency can be read with a Frequency meter at the feed through marked, CHOP CLK. Normally the frequency is set to 40 Khz by default.