Sony DXC-S500, Service Manual

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6-7
DXC-S500 (E)
PWM converter
Channels 1 and 2 are a voltage comparator that has two inversion input pins. They are a voltage-to-pulse
converter that controls the ON time of an output pulse according to the input voltage.
Channels 3 and 4 are a voltage comparator that has one inversion input pin. They are a voltage-to-pulse
converter that controls the ON time of an output pulse according to the input voltage.
An output transistor can be turned on while a chopping wave oscillation waveform is lower than an
amplifier output signal and DCT signal. The output current is 30 mA (maximum).
Channel control function
IC201 can independently control a four-channel power supply circuit. However, the DXC-S500 is
designed so that the circuit output is obtained when the voltage level is high with pins 20, 21, and 22 of
IC201 connected. This time, the voltage level is always in the high-level state.
Protection function
Timer latch-type short-circuit protection circuit
An SCP comparator detects each comparator output voltage level for output short-circuit detection.
When at least one output voltage exceeds 2.1 V, a timer circuit operates and the capacitor externally
installed at pin 23 (SCP pin) of IC201 starts charging. A latch circuit operates when an output voltage
does not return to the normal voltage until this voltage increases to a Vbe voltage. At that time, an output
transistor is turned off to stop the function. The power can be turned on again for recovery when this
protection circuit operates.
Malfunction prevention circuit at the time of low input voltage
The transition state during the power-on sequence or the instantaneous decrease in a supply voltage
induces the malfunction of a control circuit and causes the damage or deterioration of a system. At the
time of a low input voltage, the malfunction prevention function turns off an output transistor to prevent
malfunction by detecting the level of a supply voltage and resetting a latch circuit.
A voltage of
+
3.3 V is generated using Q303 and sent to the FM-84 board. A voltage of
+
5 V is
generated using Q304 and sent to the SY-301 and FM-84 boards. A voltage of
+
3.3 V is generated using
Q305 and sent to the 3 V circuit on the SY-301 board. A voltage of
+
2.5 V is generated using Q306 and
sent to the 2.5 V circuit on the SY-301 board. Connector CN301 supplies the power of the fan motor
mounted inside of CCU.
2. 2/5 circuit
This circuit is connected with CHU using a cable. This is a gigabit transceiver that transmits video data
and performs serial communication.
Gigabit transceiver (IC401)
IC401 consists of a transmitter that encodes 16-bit parallel input data, converts the data into 20-bit serial
data, and outputs it as a differential signal with an amplitude of about 0.5 V and a receiver that decodes
20-bit differential serial input data and outputs it as 16-bit parallel data. In this unit, the transfer rate of
the differential serial data is 20 times the normal, that is, 900 Mbps (Mbits/sec) because 45 MHz is used
as a clock of parallel data. By mutually connecting with the gigabit transceiver on the CA-46 board of
CHU, a 10-bit video signal, timing pulses (HD, VD, and ID), and serial communication data to a
microcomputer are received in the route of CHU to CCU. A serial communication clock from a
microcomputer, serial data, chip select signals of each device, and an external trigger signal are
transmitted in the route of CCU to CHU. X401 that generates a master clock of IC401 is 45 MHz VCXO
that is the same as CHU. However, the frequency is fixed with the control voltage (at pin 1) made stable.