Fluke 5500A, Service Manual

Page: 139 / 296

SC600 Option
Theory of Operation
6
6-13
6-22. Time Marker Mode
There are 3 primary “ranges” of time marker operation: 5 s to 20 ms, 10 ms to 2
µ
s, and
1
µ
s to 2 ns.
The 5 s to 20 ms markers are generated on the A6 DDS board and are passed to the A50
board. The signal path is also split to drive the external trigger circuitry on the A50
board. If turned on, the trigger is connected to the Trig Out BNC on the front panel. The
marker signal passing through the A50 board is connected to the attenuator assembly.
The signal is then passed to the SCOPE connector BNC on the front panel.
The 10 ms to 2
µ
s markers are derived from a square wave signal that is generated on the
A6 board and passed to the A50 board for wave shaping and external trigger generation.
If the trigger is turned on, the signal is connected to the Trig Out BNC on the front panel.
The marker signal is passed from the A50 board to the attenuator assembly and then to
the SCOPE connector BNC on the front panel.
The 1
µ
s to 2 ns markers are generated from the leveled sine wave generator on the A50
board. This signal is also split to drive the external trigger circuits. If the trigger is turned
on, the signal is then connected to the Trig Out BNC on the front panel. The other path
routes the signal to the marker circuits on the A50 board, where the signal is shaped into
the other marker waveforms. The marker signals are passed from the A50 board to the
attenuator assembly and on to the SCOPE connector BNC on the front panel.
6-23. Wave Generator Mode
All signals for the wavegen function are generated from the A6 board and are passed to
the A50 board. They are then sent to the attenuator assembly, where range attenuation
occurs. Wavegen signals are then sent to the SCOPE connector BNC on the front panel.
Pulse Generator ModesVideo and pulse generator mode signals are derived entirely from
dedicated circuitry on the A50 SC600 option board. If there are faults associated only
with these functions, the A50 board most likely needs replacement.
6-24. Input Impedance Mode (Resistance)
The reference resistors for this mode are on the A50 board, while the DCV reference
signal and measuring signals are on the A6 DDS board.
6-25. Input Impedance Mode (Capacitance)
Capacitance measurement circuits are contained on the A50 SC600 Scope Option board,
utilizing signals from the leveled sine wave source. If there are faults associated only
with capacitance measurement, the A50 board most likely needs replacement.
6-26. Overload Mode
The source voltage for the overload mode is generated on the A51 Voltage/Video board
of the A50 SC600 Option board. The voltage is applied to the external 50
Ω
load, and
the circuit current is monitored by the A6 DDS board.