B8 Chassis Power Supply Block - Philips B8 Series Service Manual

Horizontal/Vertical Processing block is applied internally within IC271.
Brightness, Picture, Sharpness, Color, and Tint control voltages are applied to IC271 from
Microcomputer, IC300 via the IIC Bus. The Red, Green, and Blue signals are developed within
IC271 and output via Pins 21, 20, and 19. The Black Current Level Set is Output from Pin 18.
The Red, Green, and Blue video signals from IC271 are applied to the CRT Board. On the CRT
Board, these signals are amplified before being applied to the CRT. The Drive and Cutoff
controls for CRT Set-Up are controlled by the microprocessor via the IIC Bus using the Service
Test Mode.
Horizontal and Vertical signals are also developed within IC271. Adjustments for Horizontal
Centering, Vertical Centering, and Vertical Height are accomplished with the Remote Transmitter
via the Service Test Mode. There is no adjustment for the Horizontal Oscillator. The horizontal
circuit is a count down type of system that gets its base frequency from the 3.58MHz circuit.
The horizontal signal is applied to a Horizontal Driver, Q502, where the signal is amplified and
transformer coupled to the Horizontal Output transistor, Q503. The output from Q503 drives the
Integrated Flyback Transformer. The IFT develops the High Voltage, Screen Voltage, Focus
Voltage, and Filament Voltage for the Picture Tube. If the voltage in T501 (T502 for 25 and 27
inch sets) goes high, a sample is sent to Q540 and Q541, the shutdown switch. This will enable
lowering the High Voltage when it starts to elevate. Scan derived voltages provided by the IFT for
use by the chassis are the 200V, +1 3.5V, and -13.5V Sources. A horizontal pulse is also made
available for the chassis from the output circuit of the Horizontal Output transistor.
The Vertical signal exits TC271 at Pin 7 and is applied to the Vertical Output Integrated Circuit,
IC550. The vertical signal is output from IC550 and applied to the Vertical Yoke. Vertical
Centering and Vertical Height adjustments are performed via the Service Test Mode and Remote
Transmitter. Vertical feedback is returned to IC550, Pin 1.

B8 CHASSIS POWER SUPPLY BLOCK

When a 120Vac Source is connected to the B8 Chassis, approximately I60Vdc is developed by