Agilent Technologies 16900A, Service Manual

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124 16900A, 16902A, and 16903A Service Guide
8
Theory of Operation
built into the ATX board are PS/2, serial port, parallel port,
USB 2.0, 10/100 Mbit LAN, and VGA Video. Additional PCI
slots are available for added I/O such as 1 Gbit LAN or
video.
Disk drives
The frame contains a standard IDE hard drive and a low
profile CDRW drive. Both are logically controlled directly
from the CPU motherboard.
Power supply
The frame uses a modular power supply to provide the six
DC voltage rails: - 12 V, +12 V, - 5 V, +5 V, - 3.3 V, +3.3 V.
These rails use remote sensing to maintain .01% load
regulation. The module slots are limited to 100 W each and
the instrument as a whole to 600 W.
The frame has a "soft" power on/off algorithm. Pressing the
power switch notifies the CPU to either wake up or power
down. The CPU then in turn drives the signal line which
actually turns the supplies on or off. A PLD monitors this
process and will force a power down after approximately
two minutes if the CPU does not respond. The small
portion of circuitry involved in this process is powered from
an aux5 V which is always present as long as the
instrument is plugged in. Additional logic monitors the
voltage levels on the six rails and will also cause an
immediate power down if any one drops below about 90% of
regulation. Power down can also be caused by an over
temperature sense circuit. In this case PLD notifies the
CPU, the user receives a warning window and a soft power
down is started. Again the PLD will force a power down if
the CPU does not soft power down in about two minutes.
16903A PCI board
The 16903A PCI Board plugs into a CPU Board PCI slot,
providing the interface between the CPU motherboard and
the logic analyzer. On the PCI board is a PCI bridge chip
used to provide an electrical interface between the CPU PCI
slot bus and the two PCI devices located on the Module
Interface Board. A TI2050A PCI bridge chip is used to
connect to the primary PCI bus on the CPU motherboard
connector and provides a secondary PCI bus, which is
connected via an 80- pin high- density cable from this PCI
board to the Module Interface Board.