Tektronix RSA3300A, Service Manual

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Theory of Operation
3- 6
RSA3303A & RSA3308A Service Manual
The A70 DC Power board is equipped with multiple DC/DC converters, and
based upon the output voltages supplied by the Power Supply 1 and 2 units,
power voltages other than above are generated on this board. On the A70 DC
Power board, LED indicators and test points are provided to facilitate checking
that all the power supply voltages are output normally.
Power Supply 3 is the standby power supply unit which continuously supplies
power to some areas of the CPU board and the 10 MHz Reference Oscillator
even if the Power Switch on the main unit is turned off (standby mode). Unless
the Principal Power Switch (located on the rear panel) is turned off, Power
Supply 3 continues to output power voltages. Because of this, remove AC power
before opening the enclosure to service inside the unit.
The Standby Power Supply always maintains the ACPI (power control) function
for the CPU board to be active. With this function, the CPU board recognizes the
On status of the On/Standby Switch even in the power-off condition and is able
to output the power-on signal to Power Supply 1 and 2 units. To enable accurate
high frequency measurements just after power-on, power is also supplied to the
10 MHz Oscillator (OCXO) from Standby Power Supply unit.
The A50 Mother board distributes power to all boards/modules, as well as
interfacing of control signals and data with the CPU. Other devices such as the
PCI Bridge, Local Bus Controller, and Bus Buffer for CPU bus expansion are
also on the A50 Mother board.
External Interface
A microprocessor for key control is installed on the A60 Front Key board.
Various processes such as serial conversion of key scan, key code, and signal
transmission to the CPU board are performed on this board.
The A62 Front Connection board interfaces with peripheral devices such as
HDD, FDD, LCD, USB, and keys with the CPU board.
The GPIB controller is also installed on the Front Connection board, and its
output bus is connected to the GPIB connector located on the real panel through
the A50 Mother board and the A70 DC Power board.
A70 DC Power Board
Standby Power and
On/Standby Switch
A50 Mother Board
A60 Front Key Board
A62 Front Connection
Board