Service manual

PV152 3-1 PROJO
CIRCUIT DESCRIPTION
POWER SUPPLY OPERATION EXPLANATION
POWER ON AND OFF
The power supply in the ZP94 & 95 chassis works very simi-
lar to the previous models, with only a few exceptions.
This power supply runs all the time when the AC is applied.
The use of the power supply creating Standby Voltage sup-
plies eliminates the need for a Standby transformer. The
following explanation will describe the Turning ON and OFF
of the projection television. The Microprocessor I001 gen-
erates the ON-OFF control signal from pin (53). The logic
states of this pin are High = On and Low = Off. When the
set is turned On, the high from pin (53) is routed to the
Relay Driver Q002 base. This turns on Q002 and it’s collec-
tor goes low. This On/Off from the Relay Driver Q002 will
perform the following :
· Turns on the SW5+V I907 and SW+12V I908 regulators.
Which do not operate in Standby.
· Turns on the Shut Down “Power Shorted” detection cir-
cuit, Q908 and Q909.
· Turns on the Horizontal Vcc supply to the Horizontal and
Vertical drive IC, I701.
· Turns on the Relay providing AC to the Deflection Power
Supply on the Power/Deflection PWB.
B+ GENERATION FOR THE SUB POWER SUPPLY DRIVER IC:
Vcc for the Driver IC is first generated by the AC input.
This voltage is called Start Up Voltage. I901 requires 21V
DC to operate normal. However, it will begin operation at
14.5V DC on pin (4) of I901.When AC is applied, AC is
routed through the main fuse F901 (a 5 Amp fuse), then
through the Line filters L901, 902, 903 and 904 to pre-
vent any internal high frequency radiation from radiating
back into the AC power line. After passing the filters it
arrives at the main full wave bridge rectifier D901 where it
is converted to DC voltage. One leg of the AC is routed to
a half wave rectifier D902 where it is rectified, routed
through R905 and R906 (both a 5.6K ohm resistor), fil-
tered by C907, clamped by a 30V Zener D904 and made
available to pin (4) of I901 as start up voltage. The Red
LED D903 is illuminated by this power supply. When this
voltage reaches 14.4Vdc, the internal Regulator of I901 is
turned On and begins the operation of I901. The primary
control element of the power supply is I901 (the Switch-
ing Regulator IC), in conjunction with transformer T901.
These two components, along with the supporting circuitry,
comprise a closed loop regulation system. Unlike previous
Pulse Width Modulated (PWM) Switch Mode power sup-
plies, the regulation system in the this chassis utilizes Fre-
quency Control Modulation with an operational frequency
of 85KHZ to 100KHZ, corresponding to full load and no
load conditions, respectively. Primary regulation is pro-
vided by Q902, I902 and Q910, regulating the switching
frequency at pin (3) of I901 via pin 1, the regulation in-
put to the IC. Three primary voltages are developed that
are needed to sustain run, maintain regulation, and sup-
port shutdown circuitry; Run Voltage generated from pin
(8 and 9) of T901, +28V used for regulation, and STBY
+11V, respectively. The “STBY” represents “always on, des-
ignating a supply that is active whenrver the unit is con-
nected to AC power. The Power Supply utilizes a Shutdown
circuit that can trigger Q905 from 16 input sources. (6 of
these are not operational in Standby mode). I903 is acti-
vated by Q905, applying gate voltage to Q901, which
grounds out the Vcc at pin (4) of I901, disabling the
power supply.
Audio Front 29V Regulator SW+29V indicated by D912:The
Audio Front 29V supply is generated from pin (17) of T901.
This output is protected by E992, rectified by D910 and
filtered by C918. This supply is routed to the Rear Audio
Output IC IC01. This voltage is what illuminates the Green
Visual Trouble Shooting LED, D912.
STBY+11V Regulator I906 indicated by D949: The STBY+11V
supply is generated from pin (11) of T901. This output is
rectified by D918 and filtered by C928. This supply is routed
to the Stand By +11 Regulator I906 pin (1). This voltage
is what illuminates the Green Visual Trouble Shooting LED,
D949.
STBY+7V Regulator I905 indicated by D927:The STBY+7V
supply is generated from pin (11) of T901. This output is
rectified by D918 and filtered by C928. This supply is routed
to the Stand By +7 Regulator I905 pin (1). This voltage is
what illuminates the Green Visual Trouble Shooting LED,
D927.
The sub power supply in theZP94 & 95 chassis works very
similar to the previous models, with some very significant
exceptions. This power supply runs at 50% efficiency when
the AC is applied with the set OFF. The use of the power
supply creating the STBY+11V supply eliminates the need
for a Standby transformer. The following explanation will
describe the Turning ON and OFF of the projection televi-
sion.
POWER SUPPLY OPERATIONAL FREQUENCY DURING STAND-
BY:
When the Horizontal deflection is defeated, the power supply
no longer has a deflection load. This low current demand is
detected by the three resistors connected to the source of
the internal Switch MOS FET inside I901 via pin (2). Pin
(1) of I901 is the over current detection pin, however it is
also the current demand sensing pin. When the current
demand is low due to horizontal defeat, pin (1) will be less
than 1.4V and the internal frequency will switch to 200Khz.
This is caused by the Quasi Resonant circuit operation.
This reduction of power supply frequency will move the
frequency above the Bell of the power supply transformer
and all secondary voltages will reduce to approximately 1/
2 of their normal voltage.Due to the fact that the power