Service manual

CB-4
CB CIRCUIT DESCRIPTIONS
The B+ provides power for deflection via the horizontal output transistor (HOT), QX3204, and for the
tertiary voltages that come from the flyback transformer, TX3204. It also develops the +33VSB for the
tuner through RX3413. The +12VSB is regulated down to +5VSB by ICX3402. This +5 volt source
powers the microprocessor and EEPROM (IC6000 and IC6001 respectively), the Gemstar
®
board, the
PiP board, and the tuner. The +15VSB is used as is to power sweep correction, horizontal drive amplifica-
tion, and the ABL circuitry. It is also regulated by ICX3401 for +9V and by ICX3405 for +12VSW. Both
of these voltages are used as various video and IF supplies. The +22VSB is used to power the audio
amplifier.
Two other voltages should be named here, although they are developed from the sweep transformer,
TX3204. Namely the + and  14VDC pass through the secondary of the switch mode power supply
section. These become the +/- 14AUD volts that power the variable audio output amplifier when they pass
the series resistor and inductor arrangement shown on the schematic.
Some of the above voltages are switched on when the television powers up, rather than when it is just
plugged in. These include +9VSW, +9VIF (some models), +9VSWF, +15VSW, and +12VSW. These
are switched upon receiving a power on DC level from pin 32 of the microprocessor, IC6000. This
switches Q3402, which in turn activates both Q3405 and Q3404.
Degaussing Control
Degaussing is software-controlled by a signal from IC6000. When the receiver is switched on, pin 33 emits
a 760 ms signal that closes the degaussing relay, KX3401, via Q3403. This allows a brief moment of AC
current to magnetize the degaussing coil before the thermistor, THX3415, limits the coils power.
<<Figure CB-5>>
KX3401
DX3405
Q3403
THX3415
+15VSB
R3419
2
1
Filtered
AC Line
Degaussing
Control, Pin 33,
IC6000
3T8 -- To
Degaussing
Coil
Part Location Part # Notes
ICX3401 F-52403 All Models
ICX3402 F-53046 All Models
ICX3403 162-00028-01 All Models
ICX3405 221-00167-05A All Models
ICX3406 221-00265-03A All Models
ICX3412 F-53857 All Models
TX3401 095-04576 All Models
<<Table CB-1>>