Philips 13PR19C1, Service Manual, Page: 63 / 365

Amplifier 7954 or 7953 by a control line from the Microcomputer 7600 Pin 2. Volume for the Normal Stereo
is controlled in the Stereo Module by a control line from the Microcomputer 7600 Pin 2. Volume control for
the DBX Stereo is controlled in the Stereo Module by the Microcomputer via the I2C bus.
Composite Video from Pin 6 of 7250 is buffered by 7266 and sent to 1200, a 4.5MHz trap, to remove any
sound. The Video is then applied to Pin 13 of 7250. The Internal/External switch selects between Pin 13 or
the External Video source on Pin 17. The selected Video is fed to an internal Y/C separator inside 7250.
Luminance and Chroma is fed to an internal SVHS switch which selects between internal Y/C or external
Y/C on Pins 11 and 10. Internally selected ”C“ Chroma is fed to an internal Demodulator which outputs R-Y
and B-Y on Pins 30 and 29. Internally selected ”L“ Luminance is output on Pin 28. R-Y, B-Y, and ”L“ are fed
to the Matrix circuit on Pins 31, 32, and 27.
Red, Green, and Blue On-Screen display signal from the Microcomputer 7600 Pins 34, 33, and 32 are fed to
the Signal Processor 7250 Pins 23, 24, and 25. Fast Blanking from 7600 Pin 35 is fed to 7250 Pin 26.
Brightness, Picture, Sharpness, Color, and Tint control voltages are developed within 7250 from the Tuning
System Microcomputer 7600 via the I2C bus. The Red, Green, and Blue signals developed by the signal
processor, 7250, are output on Pins 21, 20, and 19 and applied to the CRT board. On the CRT board, these
signals are amplified before being applied to the CRT.
The White Balance controls for the CRT set-up are controlled within 7250 by the Microcomputer via the I2C
bus. Adjustments are performed with the set in the Service Test Mode. Always use the procedures in the
Service Manual for setting up the CRT circuits (White Balance). The White Balance is set by adjusting the
White Tone adjustments in the Service Test Mode.
Horizontal and Vertical signals are also developed within 7250. Adjustment for Horizontal and Vertical
Geometry are done 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.
When the set is turned On, the Low on Pin 19 of 7600 is removed allowing the On/Standby line to go High.
The High is applied to 7607, the Astable Multivibrator, which is powered by the +5VD supply. The Astable
Multivibrator 7607 provides Horizontal Drive to drivers 7608 and 7400. The drive is then applied to 7402, the
Horizontal Output transistor, which drives the Horizontal Deflection Yoke and the IFT. The IFT develops
high voltage, focus voltage, and filament voltage for the CRT. Scan derived voltages produced by the IFT
are 160 volts, VLOTAUX13V 13 volts, -13 volts, VLOTAUX5V 5 volts, and VLOT8V 8 volts. The scan
derived VLOT8V 8 volt supply produces the +8VA supply which is applied to Pin 37 of 7250 to power the
Horizontal and Vertical sections of the IC. The Horizontal Oscillator section of 7250 does not operate until
the Scan circuit is working. Horizontal Drive on Pin 40 is applied to 7607 to synchronize the Astable
Multivibrator to the correct frequency.
The Shutdown circuits of the set monitor for excessive Beam Current, excessive High Voltage, or a Low +13
volt supply (VLOTAUX13V). The BCL_PROTN circuit of the IFT monitors for excessive Beam Current. If
the BCL_PROTN line goes High, transistor 7611 will turn On causing Pin 16 of 7600 to go Low, turning the
set Off. Transistors 7403 and 7404 monitor the secondary of the IFT for excessive voltage. If the output of
the IFT should go too high, the HEW_PROTN line will go High, causing Pin 50 of 7250 to go High. This will
shut the Horizontal Oscillator Off. Transistor 7621 and Zener Diode 6612 monitors the 13 volt
(VLOTAUX13V) line. If the 13 volt supply should go Low or fail, 7621 will turn On causing Pin 16 of 7600 to
go Low, turning the set Off. Transistor 7620 provides a power On delay for this circuit.