Power Supply Systems - Sony CBK-HD01 Maintenance Manual

1-2-9. Power Supply Systems

CNB-25 board
The board checks the input voltage +12 V, and controls
distribution of the input power to each circuit board.
• Power ON/OFF Control
The ON/OFF control is performed in IC1 and IC5. The
IC1 input signals include L PWR SW ON signal, H
POWERW HOLD signal, EXTDC detection signal,
battery detection, excess voltage detection, and low
voltage detection. During normal operation, when L
PWR SW ON signal is turned to "L", Q4, 5, 6, and 7 or
Q11, 12, 15, and 16 are turned on, and the battery or
EXT DC IN +12 V is supplied to respective circuit. The
H POWERW HOLD signal is sent from the FP-157
board after the main power of this unit is turned on.
Therefore, the power is kept on even if the L PWR SW
ON (L) signal is set to OFF (H). In order to turn off the
main power of this unit, the L PWR SW must be turned
off (H) and the H POWERW HOLD signal must be
opened and set to "L". When the FP-157 board detects
that the POWER switch is turned OFF, it sets the
POWERW HOLD signal to "L" to turn off the power
after a disc operation is completed if the equipment is in
the midst of operating a disc.
• Battery/EXT DC selector
The EXT DC voltage is detected and either battery or
EXT DC is selected with priority given to the EXT DC.
The IC5 performs the control and Q4, Q5, Q6, and Q7
are turned on when a battery is selected and Q11, Q12,
Q15, and Q16 are turned on when the EXT DC is
selected.
In this IC5, a step-up circuit (Vcc +8.5 V) that drives the
N-CH MOS FET gate is employed.
• Protection from Excess Input Voltage
VOLTAGE DETECT (IC18) monitors the input +12 V.
If the voltage exceeds approximately +18 V, the output
of the IC18-1 is set to "H". This is input to IC1 to start
the protection from the excess voltage and turn on the
+12 V output. (SHUT DOWN)
Since this function is a latch operation, the main power
of the unit needs to be turned off once and back on after
PDW-700/V1 (E)
the input power is set to below 18 V.
• Excess current detection
The output circuit of the UNREG +12 V has excess
current detection resistors R70, R71 and R72. A voltage
drop at the resistors is detected by the IC5.
When the voltage drop at the resistors exceeds 200 mV,
the +12 V output is turned off.(SHUT DOWN)
Another SHUT DOWN signal is the H SHUT DOWN
signal that is supplied from the RE-246 board. If any one
of the DC-DC converter outputs is shorted, the output 12
V enters the SHUT DOWN state except UN SW +12 V.
(SHUT DOWN)
Since this function is a latch operation, the main power
of the unit needs to be turned off once and back on after
the cause of the excess current is removed.
• Protection against input power connection of reverse
polarity
If the input power is connected in reverse polarity, FET
(Q2) is turned off so that the GND lines of the control
system circuits are disconnected. Thus the control
circuits are protected and supply of +12 V power to the
respective circuits is stopped.
• FAN voltage control
The Q13 and Q14 are controlled by the FAN CONT
signal from the AT-177 board and the PWM wave is
converted to the DC voltage according to the DUTY.
The voltage controls the FAN and reduces the tempera-
ture increase.
• Audio Circuit
This is the output circuit for the AUDIO OUT (rear
connector). The signal is output by selecting the CH1/2
or CH3/4 in the MONITOR.
• ± 4.8 regulator circuit
This is the voltage regulator for AUDIO using on the
AXM-38 board.
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