Service manual

PV152 3-3 PROJO
CIRCUIT DESCRIPTION
HIGH VOLTAGE DRIVE CIRCUIT:
When QN04 is turned on, the 11V standby will also be ap-
plied to the High Voltage Drive IC IH02 pin 14 via RN15
and DN13. When this occurs, the IC will stop generating
the drive signal that is used to produce High Voltage via
QH08, the High Voltage Driver. Again, this is done to pre-
vent CRT burn, especially during sweep loss.
GREEN LED:
The Deflection B+ 120V supply is generated from pin (13)
of TP91. This output is rectified by DP11 and filtered by
CP17. This supply is routed to the Horizontal Drive Circuit
and the High Voltage generation circuit. This voltage is
what illuminates the Green Visual Trouble Shooting LED,
DP29
POWER SUPPLY SHUTDOWN EXPLANATION
This chassis utilizes IP01 as the Osc.\Driver \Switch for
the Deflection power supply, just as the previous chassis
have done. This IC is very similar to the previous versions,
however it does differ in Frequency (described previously).
The Shutdown circuit (cold ground side detection), is used
to turn off the Relay S901 via the following circuit, QP01
(the Shutdown SCR), Connector PQD2, Q911 the Relay Driver
and the Relay S901. The Power Supply utilizes a Shutdown
circuit that can trigger QP01 from 14 input sources. When
any of these inputs cause a high on the gate of QP01, the
relay disengages, disabling the deflection power supply.
All of the Power Supply Shutdown circuitry can be broken
down into the following five groups;
SHUT DOWN CIRCUIT:
Shut down occurs when the shutdown SCR QP01 is acti-
vated by gate voltage. When QP01 receives gate voltage of
0.6V, the SCR fires and give a ground path for the pin (5)
of Connector PQD2 called PROTECT. This Low is routed to
the Sub Power Supply PWB and is impressed on the base of
the Relay Driver Transistor Q911 turning it Off. When Q911
turns Off the Relay S901 will disengage and remove the AC
source from the Deflection Power Supply.
VOLTAGE LOSS DETECTION
1. Shorted 220V (DP31 and DP32) Inverted by QP03 then
through DP22 The cathode of DP31 is connected di-
rectly to the 220V line. If it shorts this circuit is acti-
vated and pulls the base of QP03 low. This output High
is routed through DP22 to the gate of the Shut Down
SCR QP01.
2. Shorted SW+8V (DP33) Inverted by QP03 then through
DP22 The cathode of DP33 is connected directly to the
SW+8V 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.
3. Shorted 28V (DP30) Inverted by QP03 then through
DP22 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 Misoperation (D756
and Q754) then through DP34 The Deflection circuit
generates the actual Drive signal used in the High Volt-
age section. If a problem occurs in this circuit, the
CRTs could be damaged or burnt. D757 is connected to
D759 which is normally rectifying pulses off the Deflec-
tion Transformer T753. This rectified voltage is normally
sent through D757, D756 to the base of Q754 keeping
it On and it’s 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 Trans-
former TH01 generates a pulse called Heater. (Note: This
does not go to the CRTs as heater voltage, it’s used for
Excessive High Voltage Detection. If a problem occurs
in this circuit, the Ex-cessive High Voltage Detection
circuit wouldn’t operate. It would be possible for there
to be High Voltage but the circuit detecting Excessive
High Voltage couldn’t work. DH26 is connected to DH24
which is normally rectifying pulses off the Flyback Trans-
former TH01. This rectified voltage is nor-mally sent
through DH26, DH27 to the base of QH07 keeping it On
and its collector Low. If the Heater Pulse fails to pro-
duce 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:
7. -M28V Loss Detection (DP23, DP24) RP31 (18K ohm) is
connected to the negative –M28V line and RP30 (22K
ohm) is connected to the positive +29V line. The Cath-
ode of DP23 monitors the neutral point where these
two resistors are connected. If the negative voltage dis-
appears, 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