Philips FW-C50/37, Service Manual

Page: 84 / 132

Generation of +A
Common full wave rectifying with bridge rectifier 6201, using 100% secondary winding of mains transformer
(pin 11-15).
Generation of +B1/+B2
The power supply is designed to cover both, 2-channel and 4-channel application.
While for 2-channel application only one supply vB1 is sufficient, 4-channel application requires an
additional supply part +B2 which supplies the Center/Surround-amplifiers and the +12V-regulator (current
required by 4 amplifiers would overload a single rectifier).
The supply for 2-channel versions consists of one full wave rectifier:
– 2 diodes of bridge rectifier 6201, with 6204/6205 for generation of +B1
– +B2 is connected in parallel with a bridge wire.
The supply for 4-channel versions consists of two separate full wave rectifiers:
– 2 diodes of bridge rectifier 6201, with 6204/6205 (for +B1) and
– 2 diodes of bridge rectifier 6201, with 6202/6203 (for +B2),
using approx. 70% secondary winding of mains transformer (pin 11-14 respectively pin 12-15).
DB2 Supply Voltage Generation
Generation of +C
Full wave rectifying with 2 diodes of bridge rectifier 6201, using 50% secondary winding of mains transformer
(pin 13-15/13-11).
DC Supply Voltage Gereration
Display SimpC Generation
• Supply voltages for FTD ( F luorescent T ube D isplay)
The FTD requires two supply voltages, delivered by separate windings of the mains transformer:
– 4,5V
AC
for FTD heating (transformer pin 16/17)
– -30V stabilized by the -30V regulator located on the amplifier part. The supply part delivers -35V unstabilized
(transformer pin 9/10), typical value: -35V…-45V.
• Stab5V6
Stabilizer 7201 generates the supply v5V6 for the microprocessor. In fault condition the output voltage
can rise up to approx. 17V, which would definitely damage the device. Therefore an overvoltage protection for
the +5V6 supply is implemented.
Whenever the output of stabilizer rises above 7,5V, the base of 7202 reaches 0,7V (7,5V - voltage drop on
6207), the transistor switches through and short circuits the input voltage. This causes the safety resistor 3204
to blow out and interrupt immediately.
• Temperature monitoring
The mains transformer is equipped with a NTC, embedded in the secondary winding (pin 8/9). Via the NTC
line the temperature of the mains transformer is continuously monitored by the microprocessor. Further
actions depend on the software of the set. Usually the set will be switched to standby mode when the
transformer is overheated.
• Power down (PWDN) monitoring
In order to enable proper switch off conditions the mains supply is monitored by the microprocessor via the
PWDN line.
In case of mains supply interrupts the PWDN line becomes low, while the +5V6 is still stable. This enables the
microprocessor to take actions for a save shut-down (e.g. mute, reset of electronics, release of head support
of tape deck).
Amplifier part