Service manual

PV152 3-4 PROJO
CIRCUIT DESCRIPTION
connected to the negative SW-8V line and RP25 (3.3K
ohm) is connected to the positive SW+8V line. The Cath-
ode of DP28 monitors the neutral point where these
two resistors are connected. If the negative voltage dis-
appears, 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:
9. 120V Deflection Power Supply (RP17, QP02, DP15, DP16
and DP18) If an excessive current condition of the De-
flection B+ is detected by RP17 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 DP15.
This High would be routed through DP16 through DP18
to the gate of the Shut Down SCR QP01 and Shut Down
occurs.
10. 28V Vertical IC I601 Power Supply (R645, Q609, D615,
and DP34) If an excessive current condition of the Ver-
tical B+ is detected by R645 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 D615 through DP34 to the gate of the Shut
Down SCR QP01 and Shut Down occurs.
VOLTAGE TOO HIGH DETECTION:
11. Excessive High Voltage Detection (DH31, RH54, RH55
and DH24). Sensed from the Heater Voltage generated
from pin (5) of the Flyback Transformer TH01. Also,
(DH42) sends a high command to the Horizontal Driver
IC IH02, to defeat Horizontal Drive Output 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 this voltage
goes too high indicating an excessive High Voltage
condition, the voltage divider comprised of RH54 and
RH55 would impress a high on the cathode of DH31.
This high is routed through DH34 to the gate of the
Shut Down SCR QP01 and a Shut Down occurs.
12. Side Pincushion failure generating a High. (D754, and
D753) The Side Pin Cushion circuit is comprised of I651,
Q652 through Q657 If a problem occurred in this cir-
cuit that creates a High on the cathode of D754, the
High will be routed through D753 to the gate of the
Shut Down SCR QP01.
13. Deflection B+ Too High. (DP17, RP21 and RP22 RP21
and RP22 form a voltage divider. The top side of RP22
is monitored by DP17. If this voltage goes too high,
zener DP17 will fire. This high is routed through DP18
to the gate of the Shut Down SCR QP01 and Shut Down
occurs.
14. Heater Voltage from the Deflection Power Supply Too
High Detection. (DP27 and DP28) The Heater Voltage
for the CRTs filament is generated in the Deflection Power
Supply. This voltage is monitored by DP27. If this volt-
age goes too high, zener DP27 will fire. This high is
routed through DP28 to the gate of the Shut Down SCR
QP01 and Shut Down occurs.
ABL CIRCIUT
The ABL voltage is generated from the ABL pin of the Flyback
transformer, TH01. The ABL pull-up resistors are RH58 and
RH59. They receive their pull up voltage from the B+
120V(V2 ) for Deflection line generated from the Power
Supply via TP91 pin 13, rectified by DP11, filtered by CP33
and then routed through the excessive current sensing
resistor RP17.
ABL VOLTAGE OPERATION:
The ABL voltage is determined by the current draw through
the Flyback transformer. As the picture brightness becomes
brighter or increases, the demand for replacement of the
High Voltage being consumed is greater. In this case, the
flyback will work harder and the current through the Flyback
increases. This in turn will decrease the ABL voltage. The
ABL voltage is inversely proportionate to screen bright-
ness. Also connected to the ABL voltage line is DH33. This
zener diode acts as a clamp for the ABL voltage. If the ABL
voltage tries to increase above 12V due to a dark scene
which decreases the current demand on the flyback, the
ABL voltage will rise to the point that DH33 dumps the
excess voltage into the 12 line.
ACCL TRANSISTOR OPERATION:
The ABL voltage is routed through the PSD3 connector,
through the PSZ2 connector, to the base of QX13. Under
normal conditions, this transistor is nearly saturated. QX13
determines the voltage being supplied to the cathode of
DX05, which is connected to pin 45 of the Jungle IC, IX01.
During an ABL voltage decrease, due to an excessive bright
circumstance, the base of QX13 will go down, this will drop
the emitter voltage which in turn drops the cathode volt-
age of DX05. This in turn will pull voltage away from pin 45
of the jungle IC, IX01. Internally, this reduces the contrast
and brightness voltage which is being controlled by the I
C bus data communication from the Microprocessor arriv-
ing at pin 27 and 28 of the jungle IC and reduces the
overall brightness, preventing blooming.
SPOT CIRCUIT:
When QN04 is turned on, the 11V standby will be applied
to the anode of DN11, forward biasing it. This voltage will
then pass through DN11, get zenered by DN09, and go to
pin 2 of PSD3, where it will activate the Video Mute cir-
cuitry Q022 - Q024 on the Signal PWB. This is done to
prevent CRT burn. Another input to this circuit is the I701
DAC3 line. This will activate when accessing certain ad-
justment parameters in the service mode; i.e. turning off
vertical drive for making CRT drive or cut-off adjustments.