Service manual
CB-5
Microprocessor Control
Introduction
The CB chassis employs IC6000 as its microcontroller. All end user and servicer controls are accessed
using this IC. While most of its functions will be described in terms of how they are used by other devices in
the receiver, a number of facts concerning the microprocessor and its input devices will now be presented.
The microprocessors job is to communicate control instructions and feedback information to and from
various other processors and input devices in the set. These include the video, audio, PiP, Gemstar
®
, audio
& video switch ICs, the tuners, the EEPROM, the keyboard and IR detector, and the reset IC. Some of
these use a direct connection via either switch, variable pulse, or DC level for communication. Others rely
on the I
2
C bus, also known as serial clock and data bus. IC6000 provides 2 sets of clock and data lines.
The first set is pins 37 and 39, and the second is on pins 36 and 38.
Input Devices
The IR detector demodulates pulses from the 40 kHz modulated carrier and sends the pulses to pin 15 of
the microprocessor. There a special algorithm interprets the pulses as the various commands they represent.
The keyboard is only slightly more complicated in its operation external to IC6000. It works by varying
voltage on only two input pins (7 and 8) using resistor networks. A/D converters inside the micro interpret
the different voltages. Because voltage detection is used rather than active keyboard scanning, keyboard
radiation is not a problem, but maintaining a +5VSB to within ±4% is critical. Both keyboard and IR
information enter the CB chassis through connector 2K6.
Microcontroller
VDD is provided to pin 27 of the microprocessor from the +5VSBF supply. While this voltage is relatively
low, IC6000 is fairly demanding in terms of current. This same voltage powers the keyboard and IR
detector. The +5VSBF is also used as analog VDD and enters the micro at pin 18.
IC6002 serves as a reset IC for the main microprocessor. Note that it comes in a transistor type package.
It accurately resets the micro after a power failure is detected. Pin 30 is the reset signal input for IC6000.
The micro enters reset state after detecting a low on pin 30 of 2µS or more.
When the micro receives a power on signal from either the keyboard or the remote, the degaussing control
pin 33 turns on the degaussing circuit for 760ms. At the same time a constant voltage level from pin 32
turns on the switched voltages in the power supply.
Horizontal and vertical synchronization pulses are fed into pins 1 and 2. These provide the microprocessor
the current sweep location of the beam, which is necessary to correctly interrupt main video for various
types of on-screen display (OSD). Neither of these sync pulses come directly from the IC2200 where they
are first produced. Horizontal sync is actually fed back from the sweep transformer on the flyback pulse
line. Vertical ramp signal coming from pin 5 of IC2200 feeds the base of Q6002. Sync is produced on the
collector and fed to the vertical amplifier and through R6006M to the V-Sync pin of the micro. OSD or
CC (closed captions) are sent as processed RGB (red, green, & blue) from pins 50, 51, and 52. At those
times it is necessary to blank out part of the main video, a fast-blank (FB) pulse is sent to the video proces-