M1-2 and the armature brush.
c. With the reference back at convenience outlets 3 and 4, make the following
(1) Test between A1-1 and A1-3 (rotate the speed-control knob to vary
voltage at A1-3).
(2) Voltage should not be variable at any test point on the white side of the
line when A1-3 is moved up or down on A1.
In addition to troubleshooting the electrical circuit, the following troubleshooting
guide will help you isolate system malfunctions. Table 1-2 lists the symptoms, probable
causes, and corrective actions to remedy the symptoms you will likely encounter with
the Emerson 55-JS High-Volume Suction Apparatus.
REMOVE AND REPLACE DEFECTIVE COMPONENTS
Once you have isolated the causes of equipment malfunctions or defective
components, disassemble the apparatus and remove or service the malfunctioning
parts. The following paragraphs show you how to accomplish this.
a. On/Off Switch. Disconnect the power cord from the wall outlet. Remove the
12 sheet-metal screws securing the front panel. Tip the front panel forward, face down.
Mark the black and white wires for proper re-soldering on the new switch. Remove the
bad switch and install the new one. Re-solder the previously marked wires and
reassemble the unit in reverse order.
b. Variac Control. Refer to figure 1-2. Disconnect the three wires to the Variac
speed control (A1). Loosen the Allen screw on the speed-control knob and pull the
knob off. Remove the shaft nut and machine screw securing the Variac control to the
panel. Two adjusting screws are used to adjust the speed. Replace the defective
Variac with the new control. Reassemble the speed-control assembly in the reverse