Sony KV-32HS500 Training Manual page 36

4. DA-4 & DA-4X Protection Circuits
The TV video is muted, the AC relay shuts down and the Stby/Timer LED flashes a 7X sequence.
B+OCP Protection Circuit
(Reference figure 4-4)
The current in the +135V line is monitored using R5013 and Q5004. R5013 is the current sensing resistor. The
current in the +135V line flows directly through R5013. The voltage drop across R5013 in normal operation is
very low, approximately 0.2V. So, the +135V is passed with very little loss in normal operation. The voltage on
the left side is basically equal to the voltage on the right side of R5013, and because R5013 is connected across
the base/emitter junction of Q5004, there is no 0.6V difference across the junction and Q5004 is OFF.
When the current in the +135V line begins to increase due to a defect, the voltage drop across R5013 will also
increase. Because of the increased voltage drop across R5013, the voltage on the left side of R5013 will remain
constant but the voltage on the right side of R5013 will decrease. The decreased voltage on the right side is
applied to the base of Q5004 through D5005. Once the voltage drop across R5013 is large enough to cause a
0.6V difference across Q5004 base/emitter junction, Q5004 turns ON.
Current now flows through the voltage divider consisting of R5009, R5011 and R5012. The voltage drop across
R5012 is applied to IC5007/pin 8, causing IC5007/pin 8 to become more positive then the reference voltage at
IC5007/pin 9 (3V). The output IC5007/pin 14 will go Low and turn Q5018 OFF.
A High through pull-up resistor R5104 is now applied to IC2801/pin 57 (H-Prot) through forward biased D5006.
IC2801 will mute the video and communicate via IC2801/pin 52 with IC2300/pin 31 to shut off the AC relay at
IC2300/pin 69.
The TV video is muted, the AC relay shuts down and the Stby/Timer LED flashes a 2X sequence.
FBT Over Current Protection Circuit (IK Prot. 1)
(Reference Figure 4-4)
The secondary current in FBT is monitored by Q8008 at FBT/pin 1 (ABL). The +135V is used as the reference
voltage through the resistor voltage divider consisting of R8040, R8039, R8038, R8037 and R8043. The combined
voltage drop across R8036 and R8035 is used to turn off Q8008 and trigger the protection circuit. In normal
operation, 0.6V is applied to the base of Q8008, turning it ON and a Low is present at the collector. A High at the
collector is needed to activate the protection mode.
As the current in the FBT secondary increases, the ABL line will increase current through the voltage divider
network at the top of R8035 and less current will flow through R8035. The voltage drop across R8035 will
decrease, causing the combined voltage drop across R8036 and R8035 to decrease. At the same time, the 0.6V
at the base of Q8007 is decreasing, which turns OFF Q8007 and a High will be developed at the collector
through pull-up resistor R8022. D8007 is now forward biased through pull-up resistor R8024 and a High is
applied to IC2801/pin 57. IC2801 will mute the video and communicate via IC2801/pin 52 with IC2300/pin 31 to
shut off the AC relay at IC2300/pin 69.
The TV video is muted, the AC relay shuts down and the Stby/Timer LED flashes a 7X sequence.
Vertical Deflection Protection Circuit
(Reference Figure 4-4)
The operation of the vertical deflection circuit is monitored using the feedback pulse developed at IC5004/pin 3
(vertical drive IC). The pulse is amplitude limited using D5001 (4.7V Zener diode). The pulse passes through
buffer Q5005 and is applied to the base of Q5009, turning it ON, while applying a Low to the base of Q5010,
turning it OFF. With Q5010 OFF, the V-DY feedback will be applied to IC2801/pin 56 indicating proper vertical
deflection operation.
If the Vertical deflection should cease due to a defect, the feedback pulse at IC5004/pin 3 will not be developed
(no pulse through Q5005 buffer), Q5009 will turn OFF and Q5010 will turn ON. The V-DY will go to ground
IC2801/pin 56 detects the missing V-DY and places the TV in vertical shut down.
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