Agilent Technologies 66000A, Service Manual, Page: 40 / 53

40 Diagrams
Power to the mainframe is provided by a switching power supply. Energy is stored in the magnetic field of transformer T1
when current flows in the primary, and is transferred to the secondary side when the current flow in the primary is turned
off. Primary current flow is controlled by FET switches, which are turned on and off at an 85KHz rate by U1.
Regulation is accomplished by controlling the on-time of the FET switches. U1 monitors the voltage at the secondary side of
T1 through opto-isolator U2 and adjusts the on-time of the FETs accordingly. T2 provides bias power for U1.
Power at the secondary side of T1 is rectified and filtered to p5V power to the mainframe and +5V and +28V
power to the turn-on circuits in the modules.
Sheet 3 Circuit Functions
Among the circuit components included on Sheet 1 are: multiplexers U71 and U72, demultiplexers U74 and U87, power-on
chip U68, Trigger In/Out BNC connectors J116 and J117, and DFI/RI connector TB2.
The multiplexers and demultiplexers direct the digital signals from the microprocessor and distribute them among the eight
module slot locations via J121 and J122. +5V and +28V bias power is distributed to the module slot locations via J120. U68
generates a power-on (power is available) signal to the module slot locations via J120.
Note
J120 connects to J10 on the Backplane board, J121 connects to J9 on the Backplane board, and J122
connects to J11 on the Backplane board.
The Trig IN signal from J117 is distributed to the module slot locations via J120. The Trig OUT signal to J116 is directly
received from the module slot locations via J120. The RI (remote inhibit) signal from TB2 is processed by U44. U44 also
generates the DFI (discreet fault indicator), which is connected to TB2 via opto-isolator U64.
Backplane Board Schematic
SHOCK HAZARD When servicing the Main assembly and Backplane assembly, ac line voltages are
present on the Main board and backplane connectors.
The Backplane board schematic shows the distribution of the ac power and control signals from the Main board to the eight
module connectors. There are no active components on the Backplane board.
Exploded View Diagram
The exploded view diagram at the end of this section documents how the major components of the Agilent 66000A MPS
Mainframe are assembled. Parts with "MP" designations identify components that are referenced in the parts list. Refer to
Chapter 5 for the part number and description of the mechanical parts.