Fluke 5725A, Instruction Manual, Page: 69 / 196

Theory of Operation
Detailed Circuit Description
4
4-11
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High Voltage Power Amplifier Assembly (A3)
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Power amplifier
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Harness to heat sink and its high voltage power devices
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Connections to the output transformers
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High voltage heat sink temperature monitoring circuitry
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High Voltage Sense Assembly (A6):
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High voltage sense (attenuator) and calibration circuits
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5725A input and output switching relays, relay drivers
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Analog monitor, an 8-bit dac, latch for mux, latch for dac
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Subminiature D-type connector to the 5700A
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5700A current routing circuits
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Guard crossing
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AC line power selection circuitry
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AC line inrush current limiting circuitry
Detailed Circuit Description 4-14.
Detailed circuit descriptions for each pca (printed circuit assembly) are provided next.
Individual block diagrams are provided for the Current Amplifier (A2), High Voltage
Amplifier (A3), High Voltage Sense (A6), and Digital (A5) assemblies. You may also
find it helpful to refer to the schematic diagrams (Section 9) while reading theory for
each assembly.
Interconnect Assembly (A1) 4-15.
The Interconnect assembly (A1) links the other five assemblies in the 5725A. The
interconnect assembly contains the following parts:
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Connectors and traces to interconnect the other assemblies and the fan. There are
three 32-pin DIN connectors on the Interconnect pca which connect the Power
Supply assembly (A4), High Voltage Amplifier assembly (A3), and Current
Amplifier assembly (A2). A 64-pin DIN connector links the Interconnect assembly
to the High Voltage Sense assembly (A6). A 34-pin ribbon cable connector links the
Interconnect assembly to the Digital assembly (A5). Other cable assemblies attached
to the Interconnect assembly go to the fan, High Voltage assembly output, and high
voltage transformers.
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High voltage transformer secondary-switching circuitry. Three high voltage reed
relays (K013, K014, and K015) select one of three ac voltage output transformers. A
fourth relay (K001) is a high voltage armature type that connects the secondaries of
the low-frequency transformer in either a series or parallel fashion.
The circuit board has four layers. Most connections are done on the inner two layers. One
outer layer is an earth ground plane; the other outer layer is tied to the signal VCOM.