First, it is crucial to determine which model of audio drivers are being tested.
Then, disconnect the outside speakers from the two terminals on the back of the amplifier. Put a DC ohm meter across the leads going to the tower. If the reading is higher than the listed value, then one or more of the drivers could be open, or a connection is corroded. If lower, one or more drivers or the wiring may be shorted.
Determine the resistance of the Ohm meter's own leads by touching the two test leads together. Subtract the displayed value from measurements before comparing to those given below.