Sony KDP-51WS550 Training Manual page 27

4. AX-1 Protection Circuits
Excessive HV Circuit
(Reference Figure 4-5)
The HV is monitored at FBT/pin 5 using two comparator circuits (A & B) located in IC8001. Comparator A will be
triggered when there is a sustained excessive HV (or gradual HV increase), and comparator B will trigger on a
momentary (or fast increase) HV spike. Another way to look at these comparators circuits is that they are
complementary circuits to each other to ensure shutdown under any excessive HV condition the HV and AC
power will be shut OFF.
Both comparators receive a sample of the HV from T8001/pin 5, which is input to IC8001/pin 5 and IC8001/pin3.
A reference voltage (Vref) of 2.2V is developed at IC8014/pin 3 and applied to IC8001/pins 2 and 6. Once the
voltage at either IC8001/pin 5 or 3 increases above the reference voltage due to an excessive HV conditions, a
High will be output at either IC8001/pin 7 or 1. The High output will turn ON either Q8004 or Q8003, which will
then apply a Low (or ground) to IC8002/pin 1 (V-sense) turning the HV power supply converter IC OFF. Drive to
the FBT will stop and HV will not be developed.
Once the HV power supply is turned OFF, the HV sample at T8001/pin13 is removed. The HV LVP circuit detects
the absence of voltage at T8001/pin13, which turns the AC-Relay OFF via IC0001 (Main Micro).
The unit shuts down and the Stby/Timer LED flashes a 6X sequence.
Horizontal Deflection Protection
(Reference Figure 4-5)
A sample of the Horizontal drive pulse is taken off the top of C5010. The pulse at this point is amplitude limited
using D5702 to 15V. The sample pulse is first buffer by Q5701 and Q5702 and then applied to comparator
IC8006/pin 5 through D8140. Approximately 4.3V is developed at IC8006/pin 5, making it more positive then the
reference voltage on IC8006/pin 6 (2.2V). This condition causes a High (15V) to be produced at the output of the
comparator IC8006/pin7. The 15V from IC8006/pin 7 is applied to the cathode side of the LED PH8001/pin 2,
and 15V is also applied to the anode side of the LED PH8001/pin 1. So, the LED is OFF and the collector/emitter
junction at PH8001/pins 4 and 3 is open. 2.4V is present at PH8001/pin 4.
If the horizontal drive to the deflection yoke were to cease (possible defective H-Out), there would be no sample
pulse applied to IC8006/pin 5 and IC8006/pin 5 will go to 0V. This condition will cause IC8006/pin 7 to go Low.
This Low is applied to the cathode of the LED PH8001/pin 2, the LED turns ON and the collector/emitter junction
PH8001/pins 3 and 4 conduct, applying ground to IC8002/pin 1 (V-Sense). This turns the HV power supply
converter IC8002 OFF and no drive to the FBT (HV output stops). With no drive to T8001, there will be no output
on T8001/pin 13. T8001/pin 13 is connected to IC8004/pin 7 and outputs a low to IC8006/pin 2. This will cause
a high to be output at IC8006/pin 1. This high will cause D8028 to break-over, a high will be applied to the latch
circuit of Q6532 & Q6530 and the AC relay will be shut-off.
The horizontal pulse is also applied to Q5202, which in normal operation is turned ON, applying a ground to the
anode of D5205 keeping the protection circuit OFF. If the horizontal deflection stops, Q5202 turns OFF and
D5202 forward biases applying a high the IC0401/pin57. IC0401/pin57 communicates with IC0002, which then
communicates with IC0001 to shut OFF the AC-Relay.
The unit shuts down and the Stby/Timer LED flashes a 10X sequence.
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