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CIRCUIT DESCRIPTION
The cathode of DP30 is connected directly to the 28V line. If it shorts this circuit is activated and pulls the
base of QP03 low. This output high is routed through DP22 to the gate of the Shut down SCR QP01.
4. Shorted Side Pin Cushion Circuit (D760 and Q754) then through DP34
The Side Pin Cushion circuit is comprised of I651, Q652 through Q657 If a problem occurred in this circuit
that creates a Low on the cathode of D760, the low will be routed to the base of Q754, turning it Off. This
output high is routed through DP34 to the gate of the Shut down SCR QP01.
5. Shorted Deflection Transformer or Erroneous (D756 and Q754) then through DP34
The Deflection circuit generates the actual Drive signal used in the High Voltage section. If a problem occurs
in this circuit, the CRTs could be damaged or burnt. D757 is connected to D759, which is normally rectify-
ing pulses off the Deflection Transformer T753. This rectified voltage is normally sent through D757, D756
to the base of Q754 keeping it on and its collector Low. If the Deflection circuit fails to produce the pulses
for rectification, the base voltage of Q754 disappears and the transistor turns off generating a High on its
collector. This output high is routed through DP34 to the gate of the Shut down SCR QP01.
6. Heater Loss Detection (DH26, DH27, QH07 and DP34) this voltage does not go to the CRTs.
The Flyback Transformer TH01 generates a pulse called Heater. (Note: This does not go to the CRTs as
heater voltage, its used for Excessive High Voltage Detection. If a problem occurs in this circuit, the Exces-
sive High Voltage Detection circuit wouldnt operate. So it would be possible for there to be High Voltage
but the circuit detecting Excessive High Voltage couldnt work. DH26 is connected to DH24, which is
normally rectifying pulses off the Flyback Transformer TH01. This rectified voltage is normally sent through
DH26, DH27 to the base of QH07 keeping it on and its collector Low. If the Heater Pulse fails to produce
the pulses for rectification, the base voltage of Q754 disappears and the transistor turns off generating a
High on its collector. This output high is routed through DH30 to the anode of DP34 to the gate of the Shut
down SCR QP01.
NEGATIVE VOLTAGE LOSS DETECTION
Please use the Commonly Used Shutdown Detection Circuits for the description of how the circuit works.
7. -M28V Loss Detection (DP23, DP24)
RP31 (18K ohm) is connected to the negative M28V line and RP30 (22K ohm) is connected to the
po29V line. The Cathode of DP23 monitors the neutral point where these two resistors are con-
nected. If the negative voltage disappears, the zener DP23 fires. This high is routed through DP24 to the
gate of the Shut down SCR QP01 and Shut Down occurs.
8. SW-8V Loss Detection (DP28, DP29)
RP26 (3.3K ohm) is connected to the negative SW-8V line and RP25 (3.3K ohm) is connected to the
positive SW+8V line. The Cathode of DP28 monitors the neutral point where these two resistors are
connected. If the negative voltage disappears, the zener DP28 fires. This high is routed through DP29 to the
gate of the Shut down SCR QP01 and Shut Down occurs.
EXCESSIVE CURRENT DETECTION
