52
CIRCUIT DESCRIPTION
Interaction between the Service Menu and Chassis I 2 C Data Bus controls
When it becomes necessary for the Service Technician to adjust the set, the Service Menu must be entered.
This is accomplished with the TV turned off, then by pressing and holding the INPUT Key and then the
POWER SWITCH. The Adjustment Menu will be displayed at this time. With the Service Menu activated,
the Technician moves up and down to the desired adjustment using the Remote control or front panel Up or
Down cursor keys. To make the adjustment, the Technician uses the Remote control or front panel Left and
Right cursor keys to change the data values for the particular adjustment. The Microprocessor controls the
individual IC related to the adjustment using I2C technology. I2C technology allows the Microprocessor to
control and IC using only two pins, (SCL and SDA). The following pins on the Microprocessor and the ICs
that it controls are described in the following table.
PINS
CONTROLLED ICs
2 SDA1 and 3 SCL1
I401 AV Selector, I002 EEPROM, I003 DAC 1, I004 DAC 2
59 SDA2 and 60 SCL2
U204 3D/YC, I701 Deflection Drive, IX01 Rainforest, IS03 Front
Audio Control, IS05 Front EQ, IS10 Center EQ, IS08 Center/
LFE/PinP Audio Control, IS01 DAC3, I201 1H Main Video, and
I403 H Sub Video.
57 SDA3 and 58 SCL3
IS11 Rear Audio Control.
Automatically Scanning the Tuners searching for Active Channels when requested by the Cus-
tomer from the Menu.
When the Projection is first installed, the active channels must be scanned and memorized in the Channel
Scan List. This list is actually stored within the EEPROM and the Microprocessor uses the information to
Scan up or down. Held within the Microprocessor is the Initial FCC Lookup table. This table gives infor-
mation related to all the channels frequency, band, and channel number. The frequency is actually a given
value for the Phase Lock Loop circuit within the tuner. Then band is data to tell the band selection circuit in
the tuner where the particular channel is located and the channel number is given to the microprocessor to
indicate what OSD outputs to pro-duce. When the set is first opened, its in what is called Factory Reset
Condition. For the Tuner, this means that the signal source is AIR, and channels 2 through 13 are in the
channel scan list. Before the customer runs Auto Program, they must set the signal source to the type they
are using, Air, Cable 1 or Cable 2. After the source is set, the customer then proceeds with Auto Program-
ming. When Auto Programming is initiated, the Microprocessor has a specific program to run. This program
starts by placing the tuner in the lowest channel in the lowest band. That would normally be channel 2. Then
the program instructs the Microprocessor to look for Sync. To do this, the Microprocessor actually need
Horizontal Blanking (H.Blk) at pin (49) which is labeled H.Sync and Video Sync (24) labeled Main/Sub SD
Det. Horizontal Blanking is use as a gate pulse for the coincidence detector. Within the coincidence detector
there is a circuit that monitors the timing of the Sync pulse in relationship to (H.BLK). If the signal being
checked is not in time with (H.Blk) the signal is ignored. However, if the signal being monitored is in coinci-
dence with (H.Blk), the signal is deemed to be true Video Sync and that particular channel is stored as an
active channel in the EEPROM Scan List. Then the Microprocessor sends information to the tuner to move
up one channel and the whole process begins again. This is repeated until every channel is checked. After
completion of the scan, the microprocessor retrieves information from the EEPROM concerning the first
channel in the lowest band that appears in the scan list and directs the tuner to tune to that channel.
