Hitachi C28W40TN, Service Manual

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DTT DISABLE CONNECTION
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Pin 3 is the DTT disable input from pin 7 of I006. This input is inverted and is outputted at pin 4, before being connected
to pins 12 & 13 of the analogue switch (I008).
I2C DISABLE CONNECTION
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Pin 5 is the I2C disable input from pin 33 of the microcontroller. This signal is inverted and output at pin 6 to pins 5 & 6 of
the analogue switch (I007). When the microcontroller is in the reset condition, or when the TV is in the standby state, the
I2C disable line is HIGH. This signal must be inverted to disable the microcontroller’s I2C bus from the I2C bus of the rest
of the chassis.
SCART DISABLE CONNECTION
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Pin 13 is the RS232 Scart Disable input from pin 39 of the microcontroller. This input is inverted and output at pin 12,
which is then connected to pins 12 & 13 of the analogue switch (I007). When the microcontroller is in the reset state, or
when the TV is NOT in service/diagnose modes, the RS232 transmit/receive lines MUST be disconnected from pins 10
and 12 of scart socket 2. This line must then be inverted to prevent any connection being made.
EEPROM (I005)
INTRODUCTION
The ST24C16 EEPROM, or E2 as it is commonly known, is a 16Kbit (2Kbyte) device that holds non-volatile data when power is
removed from the TV. This device can hold information for 100 programmes, such as the name, frequency, standard, AV setting,
speaker language setting and teletext favourite pages. The EEPROM also holds diagnostic fault codes used to help identify
previous faults with the chassis (see separate section that deals explicitly with this). The E2 also holds factory aligned parameters,
such as the geometry, white balance, tuner AFC/AGC, model type, cathode level, etc. The E2 also holds the user’s preferential
settings, such as the volume, balance, contrast, brightness, etc. Data is written to/ read from the device using the standard Philips
I2C protocols.
DESCRIPTION
SUPPLY/GROUND CONNECTIONS
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Pins 8 and 4 are the +5V supply and ground (0V) connections respectively. The EEPROM is powered from the +5V
standby rail so that it always has power to it, even when the TV is in standby.
I2C CONNECTIONS
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Pin 5 is the I2C Data line needed to transfer serial data between the microcontroller and itself. Data is changed when the
clock line is low and latched on the rising edge of the I2C clock.
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Pin 6 is the I2C clock line needed to synchronise the I2C data transfer. 9 clock pulses are needed for the 8-bit data and
an acknowledge bit. The I2C master clock originates from the microcontroller and operates at a frequency around
100KHz.
ADDRESS CONNECTIONS
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Pins 1 to 3 are the address lines used to select the I2C slave address of the device. On the ST24C16 device, these lines
must be connected to ground in order to access the device properly.
WRITE DISABLE CONNECTION
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Pin 7 is the I2C write enable/disable input. When this input is HIGH (+5V), all I2C writes to the device are denied. When
the pin is pulled low by the microcontroller (pin 22 E2RD), data can be written to the device. In this manner, inadvertent
write operations can prevent the I2C data from being corrupted.
74HC595 SHIFT REGISTER (I006)
INTRODUCTION
The 74HC595 is a 16-pin high-speed CMOS 8-bit shift register used for additional output port capability on the A8/D8 chassis. 8-bit
data is serially shifted into the device and then latched to the outputs when so desired. These outputs are not used when the TV is
in the standby state.
DESCRIPTION
SUPPLY/GROUND CONNECTIONS
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Pins 16 and 8 are the +5V supply and 0V ground connections respectively. This device has +5V supplied to it, even when
the TV is in the standby state. Capacitor C024 is used to de-couple the supply.
VM ON/OFF OUTPUT CONNECTION
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Pin 1 is used to turn On (LOW) or Off (HIGH) the VM (velocity modulation) circuit of some high-end chassis. This
improves the transition from black to white (and vice versa) areas of the picture to sharpen them up. This is particularly
noticeable at the outer areas of the CRT. This output pin is connected to the +5V signal supply and so is left floating when
the TV is in the standby state. The diode, D008, prevents any leakage current from flowing from pin 1 to the VM circuitry
when the TV is in the standby state.