Suggestions For Troubleshooting - QSC PowerLight Series Technical & Service Manual

Figure 2.12. These four diodes need to be replaced.
this, make sure the diodes are straight and evenly spaced, and
reposition them if necessary.
8. Solder the four diodes to the circuit board.
9. Reattach the gate drive cable.
10. Check the fuse (see Figure 2.14). If it is blown, replace it with
a slow-blow 1A 250V 5×20 mm fuse (QSC part #
MS-000113-00).
11. Repeat the procedure for the other channel's power supply
board if it also has failed or is to be updated.
Capacitor C20
Figure 2.13. Capacitor C20 may also need
replacement. See the text.
Technical Service Manual
PowerLight 6.0 II, PowerLight 6.0 PFC , and PowerLight 9.0 PFC
Figure 2.14. Fuse F1 may need replacing.

Suggestions for troubleshooting

If you are repairing a failed power supply module and not simply
upgrading a working one, you should determine whether other
components have also failed.
Typical collateral failures around PFC power supply module failures
include:
Blown high rail diodes: Check D12 and D14 for sooty or
blackened thermal grease around their edges or for any other
signs of damage. If you suspect that they might be damaged,
remove them from the circuit board and check them with the
diode test function on a DMM. Replace them if necessary
(QSC part # QD-000126-00). These diodes are clamped onto
the other heat sink, at the end next to the power transformer.
If you remove the diodes, thoroughly clean away the old
thermal grease from that portion of the heat sink and from
the mica insulators; apply fresh thermal grease when you
reassemble or replace them.
Blown driver ICs: The two MIC4452BN MOSFET driver ICs, U1
and U3, are under the MOSFET heat sink. Frequently, when
MOSFETs fail, the driver IC associated with the transistor(s)
fails, too. The IC's QSC part # is IC-000064-00.
Fuses: Conditions that cause the MOSFETs to fail also frequently
cause the fuses on the AC line filter to blow. The filter circuit
board runs along the side of the amplifier between the AC power
cable and the AC power switch. Each channel has two fast-blow
ceramic AC fuses, for a total of four (120V models: 125V 25A,
QSC part # MS-000112-00; 230V models: 250V 15A, QSC part #
MS-150250-FU). Check them and replace any that are blown.
Also on the AC line filter board are the housekeeping supplies
for each channel; if they do not work, the channels will not
start even if the power supply modules are in perfect working
order. The housekeeping supplies each use a 250V 1A slow-
blow fuse (QSC part # MS-000113-00).
Fuse F1
17