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CIRCUIT DESCRIPTION
ZP94/95 MICROPROCESSOR DESCRIPTION EXPLANATION:
The ZP94/95 Microprocessor is a Duel In-Line 64 pin chip. The Microprocessor is responsible for many
different operations related to the control of the Projection Television. Some of these controls are automatic
and some require customer intervention, either by the Remote control or front panel keys and/or by the
customers menu. When power is first applied, the Microprocessor receives its B+ voltage. This Micropro-
cessor utilizes a 3.3V power supply instead of the usual 5V as in past chassis. As the 3.3V is rising, the
Reset IC (I006) holds the reset pin (54) low long enough for the main B+ to stabilize. After stabilization, the
Reset IC brings pin (54) high. During the Reset condition, the Microprocessor is initiated into is start up
state. At the same time this is happening, the Microprocessor Oscillator is generating the Microprocessors
internal clock. The Crystal responsible for this is X001 (4Mhz) connected to pins (52 and 53). When
trouble shooting a Microprocessor for problems, its very important to remember the sequence described
above. Always examine the process before looking for any other problem area.
The order is;
1. Vcc Applies. Generated from the Always Voltage (STY+7V I905) on the Sub Power Supply then
through a 3.3V regulator (STBY +5V I008 on the Signal PWB).
2. Ground is available. Look for open traces, etc .
3. The Reset circuit is working (I006). It should hold the Reset pin on the Microprocessor low until main
Vcc becomes stabled.
4. The Oscillator is running. Be careful here because a low resistance probe will kill the Oscillator or give a
false reading.
After checking for the preliminary functionality of the circuits described above, then check for active clock
pulses leaving data port pins. (See the Data Communications Circuit Diagram for details). If some other IC
is grounding the data or clock pins, the Microprocessor will not work. This usually requires a pull-up
resistor. If no pull-up resistor is noted in the schematic, then the responsibility for pull-up lies within the
Microprocessor. Unloading the pin is a good way to investigate for pull-up. When Remote Control, Front
Keys or some internal process enters a command, the Microprocessor runs a set of predetermined routines.
These routines are hard programmed into the Microprocessor RAM and are unchangeable. There are
routine instructions that can be modified by either the customer or the Servicer and involve pre-programmed
routines and variables entered by the customer or technician. These would include such things as changing
the channel, audio set-ups, on/off timer, auto-link, etc...
CONTROL OF THE PROJECTION TELEVISION:
Receiving Inferred Remote Control Commands
Receiving Key Input Commands
Controlling the On and Off state of the High Voltage Power Supply
Interaction between the Customers Menu and Chassis controls
Outputting of On Screen Display information
Interaction between the Service Menu and Chassis I 2 C Data Bus controls
Automatically Scanning the Tuners searching for Active Channels when requested by the Customer from
the Menu
Automatically Controlling the Tuners when Channels are changed for the Main and PinP Tuners
Automatically Controlling the Video Processor (Rainforest IC) when directed by the Customer
Controlling the Audio Circuits when directed by the Customer.
Controlling Switching between Tuner (Main), AVX 1, 2, 3 and 4, Component 1, 2, and Tuner 2 (AUX) or
In From Converter.
The following section will explain the controls listed above.
