Service manual

CB-3
Power Supply
current ramp is input into pin 1 of ICX3412. This signal is then used to determine how regulation shall
occur as described below. OCP is also sensed using this pin. To prevent a false over-current detection at
startup however, a constant current sink has been included in the regulator. This measure is necessary due
to a current spike that often occurs at startup due to primary capacitance discharge.
The switch-mode regulator makes use of the resonant frequency set up by the chopper transformer and
CX3408. This resonant frequency as well as the internal oscillator determines the nature of the MOSFETs
switching. Hence, the term quasi-resonant may be applied to this regulator. Regardless of the terminology
used, the IC regulates voltage based on the following simple rule: duty cycle on-time reduces as voltage
rises, while duty cycle off-time reduces as load rises. In this manner, correct voltage is maintained at the
chopper transformer. The regulators fundamental switching frequency is 20 kHz, but when the receiver is
switched on, the regulator will operate as high as 100 kHz.
Switch-Mode Power Supply Secondary Side
The secondary side of TX3401 makes use of four separate windings, each with its own half-wave rectifier,
to develop the various voltages required by the television set. As a result there are four primary stand-by
voltages (VSB): B+ (typically +130 volts), +12VSB, +15VSB, and +22VSB. The +15 and +22VSB are
each protected by 3A/250V, slow-blow fuses, FX3402 and 3403. The B+ line has sufficient protection
from the switch mode regulator. RX3423 is a fusible resistor that protects the +12VSB line.
<<Figure CB-4>>
R
A
C
ICX3406
RX3423
TX3401
1
23
4
ICX3403
CX3432
PROV
LX3403
C3419
D3410
B+
CX3420
CX3431
+15VSB
RX3409
RX3427
CX3414
PROV
CX3417
PROV
CX3416
CX3415
RX3428
LX3415
D3409
ICX3404
PROV
RX3408
RX3421
B+
CX3427
+12VSB
L3406
C3425
OUTIN
1
2
3
ICX3402
C3426
+5VGEM
L3412
+5VPiP
W3403
L3407
+5VSBM+5VTUNE
FX3402
FX3403
LX3405
DX3418
C3423
+22VSB
C3422
C3435
D3419
PDD
LX3404
D3411
C3421
CX3424
L3414
RX3417
CX3428 CX3430
+15VSB
OUTIN
1
2
3
ICX3401
D3416
C3429
Q3405
W3405
L3409
W3404
+9VIF
+9VSB
R3425M R3426
+9VSW
LX3416
PROV
+9VSWF
CX3436
D3417
Q3402
R3418M
Q3404
R3412M
+15VSB
L3408
+15VSW
C3433
OUTIN
1
2
3
ICX3405
C3434
+12VSW
RX3413
R3410
R3411
L3410
L3411
B+
+33VSB
-14VDC
+14VDC
-14AUD
+14AUD
1
2
3
4
B+
+15VSW
IQB32B44W
IQB36B44W
ONLY
4W9
±14 Volts DC
from Flyback
Power Control
Pin 32, IC6000
9-2104
9-2105
9-2106
ONLY
3
6
8
5
7
9
1
4
3
2
1
Aud
GND
To Primary
Feedback Ckt.
Primary
Side, SMPS