Keysight Technologies Option 503 Service Manual page 300

Power Supply/Midplane Troubleshooting
A6 Power Supply Description
Control Inputs
There are a number of control inputs for the A6 Power Supply assembly. The
ones that you will want to be familiar with are:
POWER_ON_L
is a signal that when pulled low tells the A6 Power Supply assembly to turn on
all of its outputs. This signal comes from the A4 CPU board assembly and is
initiated by pressing the front panel power button.
DITHER
is an AC coupled analog signal going to the supply that is used to frequency
modulate the power supply switching frequency for the purpose of lowering
any power supply related interference. The DITHER signal is generated on the
A7 Midplane board assembly.
Control/Status Outputs
There are a number of control and status outputs for the A6 Power Supply
assembly. The ones that you will want to be familiar with are:
POWER_OK
is used to verify that the +12VD, +5.1VD, and +3.35VD are all on and within
specification. A TTL high level on this output brings the CPU out of reset and
initiates the instrument boot up process.
LINE_TRIGGER
is a TTL level signal that is synchronous to the AC line input. This signal is
typically used in spectrum analyzers to trigger an instrument sweep
synchronous to the AC power line.
FAULT_L
will be a TTL low level signal to indicate that the supply is experiencing an over
voltage, over current, or over temperature condition.
Fuse
The A6 Power Supply has no user replaceable fuse. While there is a fuse
internal to the supply this is not meant for field replacement. If the internal fuse
is blown, the power supply has experienced a major failure and should be
replaced.
Standby Supplies
The A6 Power Supply assembly has two standby supplies that should always
be on if the AC input voltage requirements are met. These are the +15VSB and
the +5.1VSB supplies. These supplies are used by the instrument to keep
certain circuits alive even when the power is turned off.
300 N9030A PXA Signal Analyzer Service Guide