4: Theory of Operation
TW7201I-MS
4-5
alphanumeric lines are also available for alphabetic characters (English) for
BITE status, and submenus for composing and receiving ALE orderwire or
data messages.
4.3
Rear Panel Assembly
4.3.1
Power Supply/
Interface
The TW7201I can be powered from an AC or DC power source. The AC
input can be configured for 120 VAC or 240 VAC. The DC input is typically
13.8 Vdc. Refer to Figure 4-3 on page 4-6 for the TW7201I AC power
distribution.
AC/DC Power
Input
The power supply/interface module is mounted to the rear panel. The voltage
input module/filter mounted on the rear panel provides connection to the AC
power source. A voltage selector card configures the AC input for either
120 VAC or 240 VAC. The selector card places the transformer T1 primary
windings in series for the 120 VAC position and in parallel for the 240 VAC
position. The output of T1 is stepped-down and goes to the full-wave rectifier
BR1. The rectifier bridge produces a DC output (typically 20 Vdc unloaded at
TP1). Diode D2 provides overvoltage protection and D3 provides isolation for
the DC input. A low voltage drop-out regulator consisting of transistors Q1,
Q2, Q3 and U1 provides 12 Vdc at TP2. If the regulators fail, zener diode D4
provides overvoltage protection. Either the front panel
PWR OFF/VOL
switch
or the rear panel power line can activate the power switch relay K1 to provide
+12 Vdc to the other boards.
Audio Interface
Voltage regulator U3 provides 8 Vdc to operational amplifier U2B which
supplies power (+4 Vdc) to op amp U2A, U2C and U2D.
U2A functions as an accessory audio transmit input buffer. The nominal
balanced input from each accessory connector is 0 dBm at 600 ohms (2 Vpp).
The
ACC 1
connector audio transmit level can be adjusted using trimmer
resistor R27. The
ACC 2
connector audio transmit level can be adjusted using
trimmer resistor R29.
Buffer amplifier U2C provides a nominal 0 dBm at 600 ohms balanced
receive output at accessory connector
ACC 1
which can be adjusted using R19.
Buffer amplifier U2D provides a nominal 0 dBm at 600 ohms balanced
receive output at accessory connector
ACC 2
which can be adjusted using R22.
Remote Line
Interface
The Power Supply/Interface board provides an interface between the rear
panel and the DHSL Modem board. The remote lines DHSL1 and DHSL2 run
through the Power Supply/Interface board to the DHSL Modem board at J10.
The main interface to the modem board is connector J5. Connector J2
provides the power to the modem board.
Содержание TW7201I
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Страница 86: ...TW7201I MS Figure 5 4 DHSL Modem Board Schematic Diagram 994184 Rev E 5 25 ...
Страница 99: ...TW7201I MS Figure 5 6 Power Supply Interface Schematic Diagram 994222 Rev D 5 39 ...
Страница 104: ...TW7201I MS TW7201I MS Figure 5 8 Switching Board Schematic Diagram 994149 Rev A 5 45 ...
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