Crown Pulse 2X1100 Supplementary Manual page 7

Otherwise continue.
4. If a failure has occurred anywhere in the output stages, check the bias servo transistor. Any failure associated with bias
transistors may result in repeat failure of the affected channel even if all other defective components have been found and
replaced.
5. If a failure is found in any LVAs, checks should continue up to the voltage translator stage.
2.2 Powered Checks
WARNING: Use extreme caution when making internal adjustments when the unit is powered.
1. Apply AC mains. The PIC microprocessor will perfom a self-test, during which time the Fault LED and both Temp LEDs will
flash. After the self-test, the AC-present LED will remain on.
2. Switch on the amplifier using the front panel switch. If the protect light is on and not flashing, this indicates a DC offset fault
on one of the channels. Remove AC mains. Disconnect the output board from the main board at the header strip on the rear.
Apply AC mains, switch the unit on, and measure for a DC offset at the output connector for each channel (WRT amplifier
ground).
3. If the protect light is flashing, check the chassis fuse on the rear of the unit. If this is OK, you will make a few simple
measurements with a DVM set to Ohms range:
4. Remove AC mains.
5. Discharge the power supply capacitors. For C75 use a 1k/5W resistor. For the bulk reservoir capacitors, use a 10k/5W
resistor.
6. Check the soft-start resistors, located between the transformer and the left heat sink. These two ceramic resistors will be
broken if the power supply is OK and there is a fault in one of the channels.
7. Measure the resistance between the following points. There should not be any short circuits or low-resistance readings.
Case of the output devices to the heat sink.
Case of the output devices to the output connector tag.
Across the outer legs of the driver transistors (BF422, BF423) on each channel.
If you have a short or low resistance at any of these points, you have located the faulty channel. If these tests do not reveal
the fault, then the fault is most likely in the power supply. The following procedure should help to locate it.
1. Be sure AC mains is removed.
2 . Separate the power supply unit and amplifier stages by breaking the links (shown in green on Diagram 1). These are
down the front part of the PCB (underside) by the capacitors nearest the connections for the four black wires, shown in blue
in Diagram 1.