Further Troubleshooting - QSC PowerLight Series Technical & Service Manual

3.3 Further troubleshooting

This procedure allows you to further isolate the problem and
determine which board or module is defective.
Start at zero volts
1. Turn the variable transformer to zero and turn the amplifier
off.
Open the amplifier
2. Remove the top cover of the amplifier. See the Servicing
chapter for instructions and diagrams.
3. Check the continuity of the two main fuses, located at the top
of the line filter assembly near the front of the amplifier.
Replace any that are open.
Ramp up the AC voltage
4. Turn up the AC voltage to about 30 volts (120-volt model) or
60 volts (230-volt model).
5. Using pliers, pull the connectors for the two housekeeping
supply wires off of the audio module of the affected channel.
Measure the voltage between the wires. It should be
approximately 40 volts DC. If the voltage is significantly lower
or is not there at all, there may be a problem with the portion
of the housekeeping supply that is on the line filter assembly.
6. If the voltage is good, reconnect the housekeeping supply
wires.
7. Disconnect the latching connector on the cabling that goes to
the input board. If the channel now starts up, then the
problem was on the input board—perhaps a defective op
amp; replace or repair the input board.
8. If disconnecting the input board did not make the channel
start up, reconnect it and turn the amplifier off.
9. Disconnect the power supply control ribbon cable from the 8-
pin header on the audio module. Attach the power supply
remote controller (See the section on servicing power
supplies in Chapter 2) to the ribbon cable.
10. Loosen the screw terminals of the five power supply wires at
the front of the audio module. Remove the wires from the
terminals and make sure they are arranged so none of them
will short out against anything.
11. Turn switch S1 on the remote controller to on and turn the
amplifier on. The LED on the remote controller should glow
green.
12. Increase the AC voltage to 65 volts (120-volt model) or 130
volts (230-volt model).
13. Measure the voltages on the supply wires 1 through 4, using
wire 0 as a reference.
24 QSC Audio Products, Inc.
TD-000083-00