Sony TVP-08, Training Manual

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105
HV Stop 1
Overview
The purpose of the HV Stop 1 circuit is to shut down the High Voltage if
the ABL voltage should become too low, if the output from the High Volt-
age Block regulation tap is too high, or if the +135 volt line should rise
above +148 volts. The ABL circuit is identical to the one in the HV Stop 2
circuit, as it is a DHHS regulation to have two of this type in a TV.
ABL
The purpose of the ABL winding of the FBT is to output a voltage relative
to the amount of current being drawn from the FBT. The ABL voltage gets
lower as more current is drawn by the FBT. This voltage is input to Q8027/
B. This voltage is normally sufficient enough to keep Q8027 ON, which
keeps its collector voltage at 0 volts. This 0 volts is applied to IC8010
where it is compared to a 5.9 volts reference set up by the voltage divider
that consists of R8106 and R8115. Since the 0 volts input at IC8010/3 is
less than the 5.9 volts at IC8010/2, the output will be 0 volts at IC8010/1.
This output is sent to D8021 and Q8019/B.
When the current draw on the FBT is too great it will cause the voltage at
Q8027/B to become low enough to turn it OFF. This causes Q8027/C to
become 12 volts. This 12 volts is applied to IC8010 where it is compared
to a 5.9 volts reference set up by the voltage divider that consist of R8106
and R8115. Since the 12 volts input at IC8010/3 is more than the 5.9 volts
at IC8010/2, the output will be 12 volts at IC8010/1. This output is input to
D8027 Or Gate. When D8027 conducts, it outputs 12 volts to IC8010/3,
which causes the output at IC8010/1 to become 12 volts. This acts as a
latch to keep the HV Stop line 12 volts once shutdown has occurred. The
output is also sent to D8021 and Q8019/B. D8021 is connected to IC1009
(not shown) and alerts the IC that a High Voltage failure has occurred.
This causes the Timer LED to flash seven times in accordance with the
self-diagnostics. When Q8019 is turned ON, it shuts down the H Drive
connected to the HV Drive circuit. This shuts down the High Voltage.
High Voltage Block Tap
IC8008/3 receives input IC8007/1 which is the buffer for the High Voltage
Block tap. It has the same voltage as the tap. This voltage is compared
to a reference of 9.3 volts input at IC8007/2 and produces an output of –
12 volts at IC8008/1.
If the voltage at IC8008/3 rises above 9.3 volts, the output at IC8008/1
would 12 volts. This output is input to D8027 Or Gate. When
D8027 conducts, it outputs 12 volts to IC8010/3, which causes the output
at IC8010/1 to become 12 volts. This acts as a latch to keep the HV Stop
line 12 volts once shutdown has occurred. The output is also sent to
D8021 and Q8019/B. D8021 is connected to IC1009 (not shown) and
alerts the IC that a High Voltage failure has occurred. This causes the
Timer LED to flash seven times in accordance with the self-diagnostics.
When Q8019 is turned ON, it shuts down the H Drive connected to the HV
Drive circuit. This shuts down the High Voltage.
+135 Volt OVP
The +135 volt line goes through a voltage divider consisting of R8134,
R8133, R8132 and R8137. This voltage is input through R8120 to IC8006/
3 and is normally 4.6 volts. This voltage is compared to IC8006/2, which
has a reference voltage of 5.1 volts input to it. Since the input at IC8006/
3 is lower than the voltage at IC8006/3, the output at IC8006/1 is 0 volts.
If the +135 volt line rises above +148 volts, the voltage at IC8006/3 will
become greater than 5.1 volts. This will cause IC8006/1 to output 12
volts. This output is input to D8027 Or Gate. When D8027 conducts, it
outputs 12 volts to IC8010/3, which causes the output at IC8010/1 to
become 12 volts. This acts as a latch to keep the HV Stop line 12 volts
once shutdown has occurred. The output is also sent to D8021 and Q8019/
B. D8021 is connected to IC1009 (not shown) and alerts the IC that a
High Voltage failure has occurred. This causes the Timer LED to flash
seven times in accordance with the self-diagnostics. When Q8019 is
turned ON, it shuts down the H Drive connected to the HV Drive circuit.
This shuts down the High Voltage.