Sony KV-32HS500 Training Manual page 32

4. DA-4 & DA-4X Protection Circuits
Inrush Current Relay Protection Circuit
(Reference Figure 4-2)
The current rating of the AC relay (RY65010) is 117mA at 153VAC. To keep the current below 117mA resistor
R6515 (Inrush Current Resistor) is in series with the AC input during the initial power-up of the TV. After the
initial power-up current surge, R6516 is bypassed when RY6502 (Inrush Relay) is energized and the switch is
closed.
The operation of RY6502 is monitored using R6516 and PH6501. If RY6502 does not function, a voltage drop
will develop across R6515, which in turn develops a voltage across R6507. The voltage across R6507 turns on
the LED and 11V is output on PH6501/pin 3. D6505 is now forward biased and a High is applied to the base of
Q6532, turning it ON, which then applies a Low to the base Q6530, turning it ON. Q6532 and Q6530 is a
latching circuit.
Once the latch is activated, the voltage at the base of Q6527 is reduced and it turns OFF, removing the ground
path for the AC Relay and it turns OFF. The TV shuts down and the Stby/Timer LED flashes a 7X sequence.
B+ OVP
(Reference figure 4-2)
The voltage level of the +135V line is monitored using IC6505. If the +135V increases at IC6505/pin 2, the
voltage at IC6505/pin 2 will decrease. Once IC6505/pin 2 decreases by 0.6V, Q6522 will turn ON. D6537 is now
forward biased and a High is applied to the base of Q6532, turning it ON, which then applies a Low to the base
Q6530, turning it ON (activating the latch).
Once the latch is activated, the voltage at the base of Q6527 is reduced and it turns OFF, removing the ground
path for the AC Relay and it turns OFF. The TV shuts down and the Stby/Timer LED flashes a 3X sequence.
Low HV Protection Circuit
(Reference Figure 4-2)
The HV level is monitored through the HV Regulator circuit. IC8004 and resistor network RV8002, R8017,
R8014 and R8015 are part of the HV regulator circuit. A sample of the HV is output at FBT/pin 13 and is applied
to IC8004/pin 5 (Buffer). Approximately 7.4V is produced at IC8004/pin 7, which is then applied to the resistor
network. Approximately 2.5V is developed at the junction of R8014, R8015 and R8017.
R8014 is the feedback path for IC8002 (HV Power Supply Converter IC) to keep the HV regulated.
R8025 is the path for the Low HV detection circuit. When the 2.5V at IC8006/pin2 decreases below the reference
voltage 2.2V at IC8006/pin3, a High will be output at IC8006/pin 1 (approximately 14V) through pull-up resistor
R8032. Zener diode D8028 (5.1V) will break down. D5007 is now forward biased and a High is applied to the
base of Q6532, turning it ON, which then applies a Low to the base Q6530, turning it ON (activating the latch).
Once the latch is activated, the voltage at the base of Q6527 is reduced and it turns OFF, removing the ground
path for the AC Relay and it turns OFF. The TV shuts down and the Stby/Timer LED flashes a 6X sequence.
FBT Over Current Protection (IK-Prot. 2)
(Reference Figure 4-2)
The secondary current in FBT is monitored by Q8007 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 Q8007 and trigger the protection circuit. In normal
operation, 0.6V is applied to the base of Q8007, 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. Zener diode D8023 (5.1V) will break down. D8005 is now forward biased and a
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