Service manual

CA-4
CA CIRCUIT DESCRIPTIONS
ICX3402 regulates from the +18 VSB to provide +5 VSB. The +5 VSB powers the microprocessor,
IC6000, and the tuner, TU6000. Additionally, part of the power from the +18 VSB supplies +18 volts to
the audio circuitry (+18 AUD). The remainder of the +18VSB power is used when the set is powered up.
This powered up voltage is typically referred to as a switched voltage (VSW). The +18 VSW powers the
horizontal drive amplifier. That same +18 VSW is also regulated through ICX3401 to produce a +9 VSW.
This +9 volts powers the video signal processor, ICX2200, and, in stereo sets, IC1400. Finally, a +15
VSW is generated from the +18 VSW using RX3428, ZDX3401, and C3460. The +15 volt supply
powers the ABL video and the variable audio output circuits.
These switched voltages turn on given a DC level from pin 32 of IC6000. This signal will of course come
on when triggered by the power on key from the keyboard or the IR detector, IR6000. The DC level at pin
32 should be near +4.8 volts DC. This will drop across R3418 and switch the base of Q3402. As this
transistor turns on, it drives Q3404 into saturation and activates the switched voltages.
Degaussing Control
Degaussing is accomplished via software in the CA chassis. At turn on, pin 33 of IC6000 generates a +4.8
volt DC level. After dropping through R3419, this DC switches on Q3403 to allow current flow through
the degaussing relay, KX3401. With the relay now turned on, filtered AC line current travels into the
degaussing coil passing through the thermistor, THX3415. 760 milliseconds after power-up, the micropro-
cessor sets the voltage to zero, and the relay opens cutting off AC to the coil.
KX3401
DX3405
Q3403
THX3415
+18 VSW
R3419
2
1
Filtered
AC Line
Degaussing
Control, Pin 33,
IC6000
3T8 -- To
Degaussing
Coil
<<Figure CA-5>>