Sony KDP-51WS550 Training Manual page 29

7, IC9201/pin 7 and IC9301/pin 7 develops an IK feedback pulse, which is directly proportional to the current
drawn by each cathode in the CRT. The IK feedback pulse passes through buffer transistors Q9102, Q9202 and
Q9302, and then the sequence of the three IK feedback pulses is applied to the base of buffer Q9104.
The three IK feedback pulses are sequentially fed into IC0401/pin 24 and monitored for amplitude variations. If
the IK feedback pulse is Low in amplitude or is missing, this indicates a weak or defective cathode. IC0401/pin
24 will detect this condition and the unit will go into IK protection mode.
The unit AC relay remains ON, Video remains with distorted or missing color depending on defective area, and
the Stby/Timer LED flashes a 5X sequence.
AX-1 Audio Protection and Zero Detect Circuits
AUDIO PROTECT
FROM
R2021
IC2000
L_OUT
FROM
R2023
C2024
IC2000
R_OUT
Audio Protection Circuit
(Reference Figure 4-7)
The main purpose of the Audio Protection circuit is to detect and trigger when DC voltage is present on the
speaker (or Audio Output IC2000/pins 3 and 23) lines. The main area of concern is in and around the audio
amplifier IC2000.
A defective IC2000 can cause a DC voltage or an Audio Imbalance to occur on the output lines, causing DC
present on the output lines.
Another area of concern is the +/-22V power supply inputs to IC2000 (IC2000/pins 2 and 22). If one of the power
supply lines are missing, this will cause a DC to be present on one of the output lines depending on which power
supply line is missing. Both power supply lines have fusible links inline (PS2001 and PS2000), which can
become an open circuit.
The protection simultaneously monitors both audio outputs of IC2000. The audio outputs are summed at the
base of Q2006 and the emitter of Q2005 through resistors R2021 and R2023. When both audio outputs are
functioning properly, the summed result should be 0V at the common connection of R2021 and R2023.
Consequently, 0V is applied to the base of Q2006 and the emitter of Q2005, putting them in an OFF condition.
AUDIO-PROT.
CN2002
CN2003
R2043
R2038
R2026
Q2005
Q2006
R2030
FIGURE 4-7 - AX-1 AUDIO PROTECTION AND ZERO DETECT CIRCUITS
IC0001
MAIN MICRO
50
31
STBY
31 5V
R6129
0V
R6130
R2051
R6128
R2044
9V
27
4. AX-1 Protection Circuits
0.12V
3Vpp
120Hz
ZERO_DET
19
CN0002
42
42
CN2003
Q6112
Q6111
STBY
7V
R?
R6127
D6119
D6116
R6124
R6125
Q6110
D6114
MA BOARD
A BOARD
ZERO DETECT
T6101
9 1
AC
INPUT
8
4
7
TVP16.4-7 1/30/04