Here is how your speed control works:
The speed control of the mixer is attained through the use of a governor assembly mounted at the rear of the control plate assembly.
The electrical circuit is made and broken by the action of the fly ball governor revolving against the control plate.
When the switch lever is moved to an ON position, the position of the control plate with respect to the governor is changed by the action of the switch lever.
Thus, when the control plate is set close to the governor, a relatively low speed of the motor causes the governor to make or break the mixer’s electrical circuit through the control plate.
When the control plate is set farther away, a greater motor speed is required before the governor starts breaking the circuit.
The action of the governor is such that the speed of the motor will remain constant for a given setting of the control plate within certain loads.
After certain loads have been exceeded, the speed of the motor will drop to meet the torque requirements of the given load.
Speed is controlled by the governor and the control plate in conjunction with the phase control.
TRIAC RMS VOLTAGE
BOTH CONTACTS OPEN - 40 VOLTS
ONE CONTACT OPEN - 80 VOLTS
BOTH CONTACTS CLOSED - FULL VOLTAGE
NOTE: The triac regulates the power the motor sees depending on control board contacts.
A device called a triac is a part of the phase control circuit.
This device determines the amount of power the motor sees dependent upon the condition of the control board contacts.
If both contacts are open, about 40 volts RMS is applied to the motor and about 80 volts is applied when either contact is closed and the other is open.
When both contacts are closed, the triac is full on; consequently, full power is applied to the motor. In this way, the speed is controlled.
If the mixer motor begins to run too fast for a
particular speed setting, one or both contacts open, which cuts back on the voltage the motor sees, thus slowing it up.
If the motor operation becomes too slow, one or both contacts will close, applying the needed voltage to the motor to sufficiently increase motor speed.
This is always accomplished through the triac.
The control plate contacts control the triac, and in turn, controls the amount of power supplied to the motor.
The control Plate for your mixer is PN
If your not good with tools / meters or tedious repairs do NOT attempt this yourself.
The service manual for your mixer can be found here