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sistor turns Off, generating a High on its collec-
tor. This output High is routed through D705 to
pin (1) of Connector PQD2 called PROTECT and Shut
Down occurs as described above.
NEGATIVE VOLTAGE LOSS DETECTION
Please use the Commonly Used Shutdown Detection
Circuits for the description of how the circuit works.
5. -28V Loss Detection (RP21, RP20, DP35, DP21 and
DP22). RP21 (15K ohm) is connected to the nega-
tive –28V line and RP20 (15K ohm) and DP35 (LED)
is connected to the positive +28V line. The Cath-
ode of DP21 monitors the neutral point where these
components are connected. If the negative volt-
age disappears, the zener DP21 fires. This high is
routed through DP22 to pin (1) of Connector PQD2
called PROTECT and Shut Down occurs as described
above.
EXCESSIVE CURRENT DETECTION
Please use the Commonly Used Shutdown Detection
Circuits for the description of how the circuit works.
6. 115V Deflection Power Supply (RP24, QP02, DP18,
DP19 and DP20), If an excessive current condi-
tion of the Deflection B+ is detected by RP24 a
0.47 ohm resistor, the base of QP02 would drop.
This would turn on QP02 and the high produced
at the collector would fire zener DP18. This High
would be routed through DP19 through DP20 to
pin (1) of Connector PQD2 called PROTECT and Shut
Down occurs as described above.
7. Vertical 28V for IC I601 Power Supply (R629, Q609,
D608, and DP31). If an excessive current condi-
tion of the Vertical B+ is detected by R629 a 0.68
ohm resistor, the base of Q609 would drop. This
would turn on Q609 and the high produced at the
collector would be routed through D608 through
DP31 to pin (1) of Connector PQD2 called PRO-
TECT and Shut Down occurs as described above.
VOLTAGE TOO HIGH DETECTION
Please use the Commonly Used Shutdown Detection
Circuits for the description of how the circuit works.
8. Excessive High Voltage Detection (DH17, RH13,
and DH15) is sensed from the Heater Voltage gen-
erated from pin (5) of the Flyback Transformer
TH01. Also, (DH14) sends a high command to the
Horizontal Driver IC IH02 to defeat Horizontal Drive
Output if this voltage goes too high.
The Flyback Transformer TH01 generates a pulse
called Heater. (Note: This does not go to the CRTs
as heater voltage, it is used for Excessive High
Voltage Detection). If this voltage goes too high,
indicating an excessive High Voltage condition,
the high will be impressed on the cathode of DH15.
This high is routed to pin (1) of Connector PQD2
PV154 - 923-03506
CIRCUIT DESCRIPTIONS
SHUT OFF DURING STAND-BY
During Stand-By, some of the secondary voltages pro-
duced are turned off, except the STBY voltages after
regulation. This could cause a potential problem with
the Short Detection circuits for shutdown. To avoid
accidental shut down, Q917 also controls the activity
of Q919. During Stand-By, the output from the Micro-
processor On/Off pin (53) is Low. This Low is inverted
by Q003 and inverted again by Q004 and this Low is
routed to the base of Q917 turning it Off. This turns off
Q917 because its base is pulled Low through D927. This
action turns off Q917. When Q917 is off, it doesn't sup-
ply emitter voltage to the Emitter of Q919. The base of
Q919 is connected to 3 Low Detection inputs from [PRO-
TECT 1], (See the Sub Power Supply Shut Down Circuit
explanation for further details). PROTECT 1 monitors
IC02, 3 & 4 on the Signal PWB. IC02 produces 5.5V,
IC03 produces 3.3V, and IC02 produces 2.2V.
NOTE: PROTECT 1 will never go below 2.2 V, unless the
2.2V line is shorted.
3-4
called PROTECT and Shut Down occurs as described
above.
9. Side Pincushion failure generating a High. (D702,
and D703). The Side Pin Cushion op-amp circuit
is comprised of I701. If a problem occurs in this
circuit it creates a High from pin 7 of I701. This
high is impressed on the cathode of D702, and
the zener will fire. This High will be routed through
D703 to pin (1) of Connector PQD2 called PRO-
TECT and Shut Down will occur as described above.
10.Deflection B+ Too High. DP17, RP26 and RP27
RP26 and RP27 form a voltage divider. The top side
of RP27 is monitored by DP17. If the Deflection
115V voltage goes too high, the zener DP17 will
fire. This high is routed through DP19 to pin (1)
of Connector PQD2 called PROTECT and Shut Down
occurs as described above.
11.SW +9V Power Supply Too High Detection. (DP29
and DP30). The SW +9V voltage is monitored by
DP29. If this voltage goes too high, the zener
DP29 will fire. This high is routed through DP30
to pin (1) of Connector PQD2 called PROTECT and
Shut Down occurs as described above.
12. ABL Voltage Too High Detection. (DP15)
The ABL voltage is generated by the voltage drop
across the ABL pull up resistors, (RH27 and RH28).
According to the Flyback current demands. (See
ABL circuit diagram for details). The ABL voltage
is clamped at a maximum of 11V by (DH16).
If the ABL voltage goes too high, the zener DP15
will fire. This high is routed through to pin (1) of
Connector PQD2 called PROTECT and Shut Down
occurs as described above.
ZP26/28 - SERVICING
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