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QSC Audio Products, LLC
9.6 Power supply, MOSFET failure (BOP)
The most common PSU failure is a failed Q13 or Q14 MOSFET. The failure can cascade down further to gate-drive compo-
nents. In some cases, the PSU will not start due to a PWM controller U15 failure.
Symptoms:
•
no power
•
The PSU attempts to start but does not succeed.
Failure verification:
•
Q13 or Q14 shorted between any two pins of gate, source, or drain.
Repair notes:
•
Use the highlighted schematic in Figure 9.9 as a component check guide. Replace components in red and check compo-
nents in blue.
•
Q13 and Q14 don’t always fail in pairs, but they should both be replaced in the event of a failure.
•
A failure of Q14 can put a huge current pulse through C112 and C113 while Q14 is failing; check for the proper rectified
AC voltage across the primary caps if the power supply appears to be dead.
•
Check gate drive components (resistors and diodes) tied to gate signals QCL-DR and QM-DR.
•
If the LEDs blink but the module won’t start, suspect a failure to the power supply controller, U15.
•
AC current draw at idle should be 0.1—0.3A at 120Vac and 0.1—0.2A at 230Vac. If the idle current is not in this range,
there is a problem.
OC = 26.1A = 0.75V
22AWG AUX
100X40AWG LITZ SEC
100X40AWG LITZ PRI
EE42 3C90
LINEUV = 1.27V
IMBD4148
20 PCNT
1.0UF
1 PCNT
1.13K
1 PCNT
1/10W
BAS21
1/10W
10
10 PCNT
25V
20 PCNT
125VAC
STW26NM60
500V
1 PCNT
2.21K
11K
1 PCNT
1/8W
82.5K
5 PCNT
1 PCNT
2W
100
1/10W
1 PCNT
2.87
220PF
50V
5 PCNT
1.00K
1 PCNT
IMBD4148
1/10W
BAS21
20 PCNT
16V
1.0UF
UCC2893
5 PCNT
5 PCNT
1W
1W
1W
1 PCNT
82.5K
1/8W
0.022UF
1/10W
1 PCNT
1/10W
63.4K
1 PCNT
6.34K
500V
10 PCNT
0.022UF
KBU1005
82.5K
1 PCNT
63.4K
MOC205R2V-M
1 PCNT
1 PCNT
1/10W
0.1UF
25V
10 PCNT
MBR230
0.1UF
1 PCNT
1/8W
10
1/8W
10
1 PCNT
MBR230
1 PCNT
21
1/10W
16V
1.0UF
20 PCNT
16V
1/10W
1/8W
1/8W
5 PCNT
1 PCNT
243
250V
0.68UF
STP11NM60FD
243
400V
20 PCNT
470UF
400V
20 PCNT
470UF
1/10W
1/10W
11K
82.5K
10 PCNT
11K
1W
5 PCNT
5 PCNT
1/10W
1 PCNT
768
220PF
10 PCNT
250VAC
0.0022UF
29.4K
11K
1 PCNT
0.022UF
1/10W
10 PCNT
500V
D40
D27
D25
D24
D23
BR1
Q13
Q14
T1
T1
T3
T3
D35
C115
C118
C128
C137
R165
R157
C116
C112
C113
C114
R144
R145
R146
R147
C124
R143
R150
R149
R151
R158
R155
R153
C117
R148
U15
R164
T2
R152
R172
T2
C52
R166
U3
R57
R168
C21
R185
R186
C130
C132
R188
R189
QCL-DR
QM-DR
PRI_LO
PRI_LO
PRI_HI
PSU-VSW
QCL-DR
PSU-VSW
QM-DR
PRI_LO
1
2
3
4
1
3
4
6
12
7
9
15
13
8
1
3
2
10
5
16
4
1
3
10
12
7
7
6
5
B2
B1
A1
A2
S10
S12
S7
-
AC2
AC1
+
P3
P1
FB
VREF
AUX
OUT
CS
SYNC
SS_SD
RSLOPE
RTOFF
RTON
RTDEL
LINEUV
VIN
Figure 9.9 - Components to replace and/or check in the event of a power supply MOSFET failure.
Summary of Contents for K8
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