Hitachi C28W40TN, Service Manual

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22
RED LED OUTPUT
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Pin 42 is the red LED output, which is used to indicate the standby state and when an IR command has been successfully
received and decoded. When the TV is in the standby state, this output will be HIGH to ensure that the red LED is brightly
lit. When the TV is not in standby, then this output will be low, but the red LED will remain dimly lit through resistor R081.
When an IR command has been successfully received, then the LED will flash briefly, to inform the user that the button on
the handset was pressed correctly.
I2C CONNECTIONS
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Pin 23 is the I2C bus data input/output for transferring data between other I2C peripherals/devices. This line is only
connected to the EEPROM (I005) when in the standby state or when writing to the EEPROM. This line is constantly active
when the TV is powered up and normally changes state between (+5V and 0V).
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Pin 24 is the I2C bus clock output for clocking the data to other I2C peripherals/devices. The clock line is also
disconnected from the main chassis when in the standby state or when writing to the EEPROM. This line oscillates at a
frequency around 90KHz
RS232 CONNECTIONS
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Pin 30 is the RS232 Transmit line from the microcontroller. It can be routed to pin 12 of the scart socket and to pin 3 of
connector P001 for the DTT module (only on D8 chassis). This line is time shared between communicating with the DTT
unit and the scart socket (for diagnostics). When the DTT disable line is LOW, the TXD line is routed from pin 1 to pin 2 of
I008 (74HC4066). When the Scart disable output from the microcontroller (pin 39) is low, then the TXD can be routed from
pin 1 to pin 2 of I007 (74HC4066). There is never a situation whereby both disable outputs are low (enabling both DTT
and SCART RS232 communications).
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Pin 37 is the RS232 Receive line for the microcontroller. It can be routed from Scart 2 RXD (pin 10) and from pin 4 of
connector P001 for the DTT unit (only on D8 chassis). When the DTT disable line is low, the DTT can transmit to pin 10 of
I008 and is then routed through to Pin 37 of the microcontroller. When the Scart disable line is low, then the data can be
routed from pin 10 of scart 2 to pin 10 of I007 and then through to pin 37 of the microcontroller. There is never a situation
when both RS232 enable lines are HIGH (disable outputs LOW).
RGB CONNECTIONS
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Pin 44 is the OSD/Teletext RGB blanking signal necessary for allowing insertion of the OSD/Teletext onto the picture.
When this output is high (approx. +5v), then the RGB signal will be superimposed onto the current picture.
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Pin 45 is the OSD blue signal necessary for displaying BLUE colours for the OSD and Teletext.
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Pin 46 is the OSD green signal necessary for displaying GREEN colours for the OSD and Teletext.
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Pin 47 is the OSD red signal necessary for displaying RED colours for the OSD and Teletext.
CVBS CONNECTIONS
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Pin 60 is the Composite Video signal input for VPS and WSS slicing. It is normally AC coupled and internally clamped to
ensure reliable operation. VPS (video programming system) is necessary when auto-sorting programmes in
Germany/Austria/Switzerland. WSS (wide-screen signalling) is used to indicate the aspect ratio of the incoming signal.
The TV can then use this information to display the picture in the correct format.
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Pin 61 is the Composite Video signal input for Teletext acquisition and decoding and also for sync extraction, necessary
for obtaining the correct line timings for slicing the teletext information and VPS/WSS information.
EPROM/MTP (I002)
INTRODUCTION
The device located in position I002 is used to store the program code needed by the microcontroller to operate the television
correctly. This 32 pin device is an MTP (multi-time programmable memory) which allows for it to be re-programmed out of the
chassis without having to erase it using conventional UV EPROM erasers. The device currently used on the A8/D8 chassis is the
MX26C1000APC, which can hold 128Kbytes of information (1Mbit). This device also holds any initialisation data to be downloaded
to an EEPROM. When a blank EEPROM is fitted, the initialisation data is automatically downloaded to it when power is applied to
the chassis.
DISCUSSION
SUPPLY/GROUND CONNECTIONS
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Pins 32 and 16 are the +5V supply and ground connections respectively. The supply voltage of +5V is always present
even when the TV is in the standby state.
ADDRESS CONNECTIONS
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Pins 2 to 12, 23 and 25 to 29 are the 17 address lines needed to access the full 128Kbytes of 8-bit data inside the device.
These lines are connected directly with the microcontroller so that it can request data from the MTP when operating. An
oscilloscope can be used to check pin 12 of the MTP to check whether the microcontroller is running correctly and
accessing the MTP. This pin should be oscillating at a frequency of around 2MHz and is a non-periodic square waveform.
DATA CONNECTIONS
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Pins 13 to 15 and 17 to 21 are the 8 data lines needed to transmit a byte at a time to the microcontroller. These outputs
are normally tri-state and are high-impedance when the output enable pin 24 of the MTP is HIGH. When the output enable
pin is low, the data from the required address will be output on these pins.