Power Supply - Zenith Presentation Series Service Manual

At the front jackpack one pair of audio jacks is used
with both the Computer and Aux. Video inputs. (If both
video inputs are in use the Aux. Video is selected as
default input.)
The rear jackpack includes one set of audio jacks for
the S-Video, another set of audio jacks for the Aux.
Video input, and a third pair for the RGB Computer
input.
The Audio processor IC1400 switches between the
Composite Audio input on pin 19 (Comp-in) from Tuner/
IF section and pins 39 & 40 (AUX1-R & AUX1-L, the L/
R channels from the A/V Switch ICX2900). The A/V Switch
chooses from among four inputs from external audio
sources (Rear and Front jackpacks). The I²C bus controls
both IC's. The power amplifier IC801 and the variable
output monitor stage take the Left and Right channels
from the audio processor Lsout-L (pin 7) and Lsout-R
(pin 6) outputs.
SWITCH THEORY
Audio source selection for CS chassis sets is made
through two internal switches SW1 and SW2 inside the
IC1400 audio processor. These switches are controlled
by EXT1 and EXT2 registers to select COMPIN Tuner /IF
signal, AUX1 (Audio/Video switch), or AUX2 (Not used).
The A/V Switch chooses one of the Audio/Video input's
external sources: Video Aux., S-Video, Rear Computer,
or Front Computer/Video.
NOTE: CS chassis does not use AUX2 input of IC1400
so register EXT2 is always 0.
The audio source selection is made through the EXT1
register of IC1400. EXT1 selects either Composite audio
or AUX1 input.
A/V SWITCHES
COMPOSITE AUDIO
Audio/Video
Switch
AUD (V-AUX)
AUD (S-VIDEO)
AUD
(COMPUTER
FRONT)
AUD
(COMPUTER
IC2900
REAR)
221-01053
SR23 - 923-03509
CIRCUIT OVERVIEW (continued)
Matrix
AUX1
SW1
TVOUT
AUX2
SW2
Volume Limiter
Surround
Bass/Treble
Balance
Volume
LSOUT
IC1400
221-01127
IIC BUS
You can choose among the following inputs: Antenna/
Cable, Aux Video, S-Video, Front Computer/Video, and
Rear Computer SVGA/Rear Computer NTSC. First the Audio
Processor selects between COMPIN (TV) and AUX1 (A/V
Switch). Then when AUX1 has been selected, the A/V
switch IC2900 selects which auxiliary input goes to
the audio processor. The table below shows the IC2900
A/V switch and IC1400 audio processor register values
and the output source selected.
The audio source selection for the audio processor is
made according the next control table:
Mode control
EXT1 EXT2
0 0
0 1
1 0
1 1
After the audio source selection is made, the sound
processor block processes the signal. The output signals
(LSOUT-L and LSOUT-R) are applied to both the Audio
power amplifier IC804 and variable audio monitor out.
The coupling between the Audio processor and the Audio
power amplifier is made through the electrolytic
capacitors C808 and C805. This is done in order to
block the DC level (4.0 V) of the LSOUT-L and LSOUT-R
pins respectively. The coupling between the Audio
processor and the variable monitor out is made through
of the capacitors C1449 and C1448.
The AV switch IC2900 has 7 audio inputs and 3 audio
outputs. Two of three outputs depend on video, and
the others are selectable from Main (Main video) or Sub
(PIP video). This chassis has no PIP.
D02 A/V switch register controls the sound selection
from Main or Sub (PIP):
D02 = 0 Main sound (Default value)
D02 = 1 PIP sound

POWER SUPPLY

POWER SUPPLY DEFINITION
The Power Supply uses a COLD chassis and is a single
sided circuit board that has been developed for screen
sizes 27" through 36". The power supply features two
switch mode power regulators for voltages sources. One
is intended for Standby sources and the other one
supplies the main switched voltages.
Both power supplies use direct regulation. One error
amplifier and one optocoupler are used for each power
supply. This chassis also is Energy Star compliant for
low power consumption in standby mode (less than 3
Watts of consumption). This is the main reason for the
standby power supply.
3-6
Audio Source selection
AUX2 LSOUT
OFF Antenna (Default)
ON Antenna
OFF A/V switch selection
ON A/V switch selection
CS - SERVICING