Philips Colour Television Service Manual page 83

Circuit Descriptions, List of Abbreviations, and IC Data Sheets
bridge rectifier is fed to the base of 7512, keeping it turned On.
This keeps Transistor 7513 turned Off. If the DC voltage drops
to approximately 75 volts, Transistor 7512 will turn Off,
Transistor 7513 will turn On, putting the anode of Zener 6516
to ground, clamping the voltage on Pin 6 at 5 volts.
The Standby supply produces the +5STDBY, +6VD supplies
when power is applied to the set. The +6VD supply feeds 7507
which produces a +3V3D supply. When the set is turned On,
the Standby line from the microprocessor on the SSB goes
Low. Transistor 7502 turns Off, turning Transistor 7500 On.
7500 turns Transistor 7505-1 On, switching the +15 volt supply
On. The +15 volt supply also feed regulator 7508 to produce
the +9 volt supply. Transistor 7505-2 also turns On, switching
the +5V2 supply On.
9.2.4 Main Power Supply
The Main Power supply is located on the Large Signal panel.
The Main B+ voltage from the Input panel is applied to the Main
Power switching transistor, 7301, via Pins 6 and 8 of
transformer 5300. This voltage is protected by fuse 1300 and
filtered by choke 5330. The Standby line goes "low" when the
set is turned "on". Transistor 7309 is turned "off", which turns
7300 "on". This turns relay 1305 "on". The Start-up voltage is
applied to capacitor 2303 via resistor 3300. When 2303
charges to 14.5 Volts, the under-voltage lockout of 7302
connected to pin 1 is turned "on". Drive is output on pin 3 to the
switching FET, 7301. This signal drives 5300 to produce the
Main Power supply voltages. IC 7302 will continue to drive
Figure 9-5 Main power supply circuit
DPTV585 AA
Under voltage Detection
Figure 9-4 Under voltage detection circuit
If the 15-Volt supply drops below 11.2 Volts, transistor 7221 will
turn "off". The 5-Volt standby supply will be applied to the base
of 7220 (Figure " Standby power supply circuit") via resistors
3262 and 3263. This will cause the +15UV line to go "high". In
the Standby mode, the Standby line is "high" turning transistor
7222 "on". When the set is turned "on", 7222 turns "off".
Capacitor 2296 provides a delay to prevent the +15UV line
from going "high" before the +15V supply turns "on".
This circuit can be defeated by grounding the base of transistor
7220. When repairs are complete, this jumper should be
removed.
5300 until the charges on capacitor 2303 drop below 9.4 Volts.
The Under voltage Lockout of 7302 will then turn the output on
pin 3 "off" until 2303 again charges to 14.5 Volts. After several
start-up cycles, the operating voltage for 7302 is supplied by
pin 10 of 5300.
Regulation is accomplished by monitoring the 130V_S supply
via resistors 3324, 3350, 3323, and 3322. The feedback
voltage is applied to the Shunt Regulator 7304, which drives
the feedback opto-isolator 7303. The feedback voltage is
applied to pin 14 of 7302. The voltage is fed to comparator "C"
which is referenced to 2.5 Volts. This output of this comparator
9. EN 83
E_15000_069.eps
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