Hv Stop 2; Overview; Abl; Hold Down - Sony TVP-08 Training Manual

HV Stop 2

Overview

The purpose of the HV Stop 2 circuit is to shut down the High Voltage if
the ABL voltage should become too low or if a Hold Down condition ex-
ists.

ABL

The purpose of the ABL winding of T8003 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. The winding at
T8003/11 goes through CN8003. CN8003 has pins 5 and 6, and 3 and 4
shorted together on the plug. CN8003/4 and 5 are shorted on the board.
The High Voltage circuit will not operate if this plug is removed from its
connector. The ABL voltage exits CN8003/3 and goes through R8161
and R8162 before being input to Q8028.
The ABL voltage is input to Q8028/B. This voltage is normally sufficient
to keep Q8028 ON, which keeps its collector voltage at 0 volts. This 0
volts is applied to IC8006 where it is compared to a 4.8 volts reference set
up by the voltage divider that consists of R8110 and R8109. Since the 0
volts input at IC8006/5 is less than the 4.8 volts at IC8006/6, the output
will be 0 volts at IC8006/1. This output is sent to D8026 and Q8021/B.
When the current draw on the FBT is too great, it will cause the voltage at
Q8028/B to become low enough to turn it OFF. This causes Q8028/C to
become 12 volts and this is applied to IC8006 where it is compared to a
4.8 volts reference set up by the voltage divider that consists of R8110
and R8109. Since the 12 volts input at IC8006/5 is more than the 5.9
volts at IC8006/6, the output will be 12 volts at IC8006/7. This output is
input to D8026 Or Gate. When D8026 conducts, it outputs 12 volts to
IC8006/5, which causes the output at IC8006/7 to become 12 volts. This
acts as a latch to keep the HV Stop2 line at 12 volts once shutdown has
occurred. The output is also sent to D8021 and Q8021/B. D8021 is
connected to IC1009 and alerts the IC that a High Voltage failure has
103
occurred. This causes the Timer LED to flash seven times in accordance
with the self-diagnostics. When Q8021 is turned ON, it shuts down the H
Drive connected to the HV Drive circuit. This shuts down the High Volt-
age.

Hold Down

Hold Down means that the High Voltage is shut down when the it exceeds
a certain level. That level is 34 KV in this set. This is done by inputting the
output of T8003/6 to a peak hold circuit consisting of D8032 and C8077.
C8077 charges to hold the peak voltage present at D8032/C. This volt-
age passes through a voltage divider consisting of R8135 and R8140
before being buffered by Q8031. This voltage then is input to a voltage
divider consisting of R8191, and the resistor network consisting of R8192,
8193, R8194 and R8202. R8202 is installed at the factory onto CN8007.
It may or may not be present in the set. This resistance is set at the
factory and its value is such that the set will shut down at 34 KV. The
voltage created by this setup provides around 4.9 volts to IC8010/5.
The voltage input at IC8010/5 is compared to a reference voltage at IC8010/
6. This reference voltage will vary between 5.1 and 6.2 volts since it is
derived from the ABL signal. The ABL signal is used as a reference
because the voltage from T8003/6 will vary if more current is drawn
fromT8003 FBT. Since the ABL voltage also varies with current draw, it
creates an acceptable reference for Hold Down. In order to create this
reference, the ABL signal is input to IC8009. IC8009 is an inverting am-
plifier that outputs the largest signal when the most current is being drawn,
which is when the ABL voltage is lowest.
If the voltage at IC8010/5 should become greater than the voltage at
IC8010/6, then the output at IC8010/7 will become 12 volts. This output is
input to D8026 Or Gate. When D8026 conducts, it outputs 12 volts to
IC8006/5, which causes the output at IC8006/7 to become 12 volts. This
acts as a latch to keep the HV Stop2 line 12 volts once shutdown has
occurred. The output is also sent to D8021 and Q8021/B. D8021 is
connected to IC1009 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 Q8021 is turned ON, it shuts down the H
Drive connected to the HV Drive circuit. This shuts down the High Volt-
age.