H Protect/Hp; Overview; H Protect - Sony TVP-08 Training Manual

H Protect/HP

Overview

The H Protect/HP circuit has two purposes. The first is to use a sample
from the Horizontal output to create the HP pulse, which is used to control
the phase of the H Drive pulse. The second is to create a HIGH output on
the H Protect line if there is a loss of the HP pulse. This HIGH is used to
trigger the latch circuit and shut down the set.
HP
Pulses from the horizontal output circuit are input to Q5019/B. This signal
cuts off the bottom of these spikes and these modified spikes are output
Q5019/E. This signal is input to Q5016/E. Q5016 is a common base
amplifier whose input is the emitter and output is the collector. This ampli-
fier squares off the tops of these spikes. This signal is the HP or HBLK
pulse and is used to control the phase of the H Drive signal, as well as the
H Protect circuit.

H Protect

The HP signal is applied to Q5014/B. Since it is a positive going pulse, it
is blocked by D5014 from Q5015/B. When the positive going pulse is
input to Q5014, it turns the transistor OFF causing 6Vpp pulses to be
present at Q5014/E. This voltage comes from the +12 volt line through
R5058 and Q5015 B-E junction. This pulse is applied to a peak detect
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circuit consisting of C5026, R5039, D5008 and C5020. As long as pulses
continue to be applied to this peak detect circuit, C5020 will hold a charge.
The voltage from this charge is enough to keep Q5006 ON since it ap-
plies .6 volts to Q5006/B. This keeps Q5006/C LOW whenever the HP
signal is present. If the pulses should disappear, the DC present would
be stopped by C5026 and C5020 would not charge, turning Q5006 OFF
and causing a HIGH output from Q5006/C.
H Protect Delay
Q5009 is the H Protect Delay and delays the operation of the H Protect
circuit until C5011 charges. When the set is turned ON, current flows to
ground through Q5009 B-E junction and C5011. This allows for .6 volts to
be present at Q5006/B until C5011 charges. The HP pulse should be
present at this time. If not, the H Protect line will go HIGH and the set will
shut down.
Q5019/B
2V 20us
Q5016/C
2V 20us
Q5019/E
2V 20us