Service manual

CA-3
Power Supply
voltage at the base of QX3401 will switch that transistor on, shunting the regulator ICs base drive to
ground. Such an action kills the regulators oscillation, thereby eliminating power generation.
Several capacitors, CX3408, CX3409, CX3410, and CX3412, are used in the SMPS to reduce EMI
(electro-magnetic interference). Additionally, RX3405 and CX3415 serve as a snubber circuit, to reduce
peak voltage on the collector (pin 3) of ICX3400s switching transistor.
Switch-Mode Power Supply Secondary Side
The two windings on the secondary side of the chopper transformer generate the regulated B+ (or simply
B+) which, depending on the size of the television, will be either +124 volts DC or +130 volts DC, and the
+18 volts DC. Both are present when AC line voltage is supplied to the SMPS. Hence these voltages may
be considered Stand-By (SB). The B+ supplies necessary power to the horizontal sweep and the horizon-
tal output sections. It is filtered and rectified using LX3403, C3419, and D3410, and it can be measured
across CX3420. Note that the B+ line does not have a fuse. The OCP circuit mentioned above serves to
shutdown the power supply if too much current is drawn through the regulated B+ circuit.
TX3401
LX3403
LX3404
DX3411
D3410
CX3424
CX3420
C3421
C3419
B+
+18 VSB
RX3428
ZDX3401
C3460
+15 VSW
R3427
R3423
C3425
OUTIN
1
2
3
ICX3402
C3426
+5 VSB
Q3406
PROV
FX3402
W3402
R3422M
PROV
L3407
R3424
PROV
D3414
PROV
Q3402
R3418
R3414
Q3404
R3412M
Q3405
PROV
R3425M
PROV
R3426M
PROV
W3401
L3405
CX3430
C3428
PROV
C3429
RX3417
OUT IN
1
2
3
ICX3401
+9 VSW
4
1
7
5
8
Power Control
Pulse from
Pin 32, IC6000
+18
VSW
+18V
AUDIO
+5V
TUNER
<<Figure CA-4>>
On the other hand, the +18 volts DC (or +18 VSB) is fused by FX3402. Rectification and filtering of the
+18 VSB is accomplished by an arrangement similar to that of the B+. The resulting +18 volts DC may be
measured across CX3424. This voltage is further broken down to provide power to various circuits
described below.