Assembly Level Repair - Keysight Infiniium 9000 Series Service Manual

4
Troubleshooting
A Command Fault happens when the ON sequence to one of the sequencers goes
HIGH to initiate a turn-on, but then goes LOW before the turn-on sequencing
finishes. Similarly, if the ON signal goes HIGH during sequencing off, a Command
Fault occurs. This kind of fault indicates something is going wrong with the ON
signal. Since the second two sequencers are fed by7 other sequencers, this will
most likely happen on the first sequencer. The ON signal is driven by the minimum
on-time limiter. There could be a problem here as well.
External Fault:
An External Fault can be caused by several failures. If a supply goes over-voltage,
an external fault is issued. If the over-temperature sensor or FPGA issues a fault, it
will be displayed as an external fault on channel 4. This present an ambiguous
case as an External Fault on channel four could occur for multiple reasons. To help
determine the cause, the over-temperature LED will light during an
over-temperature fault. However, this LED does not latch to failure. Once the
oscilloscope cools to below the over-temperature condition, the LED will turn off.
The main reason for an over-temperature fault is a stopped fan or blocked air inlet.
Check for these and power the oscilloscope back up. If it continues to shut down,
it could be a bad over-temperature sensor or comparator circuit.

Assembly Level Repair

Please read the paragraph directly below as it discusses that a fault on one
sequencer causes LEDs corresponding to other sequencers to illuminate. This is
important to understand before proceeding so you know which LED is actually the
root of the problem.
When a fault occurs on a given sequencer, it notifies the other two using the Fault
signal. The other two sequencers report this as an External Fault as well. For
example, if the first sequencer has an over-voltage on Channel 1, it will report an
External Fault with Channel 1 as the source. The other two sequencers will report
it as an External Fault with the source as Channel 4. Similarly, if the first sequencer
has an under-voltage failure on +12V, it will report a Reset Fault on Channel 1 and
the other two sequencers will report External Faults on Channel 4. As you can see,
any fault on one of the sequencers always reports an External Fault on Channel 4
on the other two sequencers. Look for the fault that is not an External Fault on
Channel 4 as the cause of the shutdown. If all three sequencers report an External
Fault on channel 4, it will take some work to determine the real source. It could be
on any of the Channel 4 sources (+2.5V, +1.2V, -3.8V), an over-temperature fault
(look for the over-temperature LED to light), or an FPGA issued fault.
Sequencer 1 Group Faults:
If the fault occurs in the first group of LEDs (Sequencer 1) then the problem is with
the 12 V bulk power supply, the power cables, or the acquisition board. You should
check the power cables first, then the bulk power supply, and finally the
acquisition board. Reinstall any power supplies, cables, or acquisition boards that
turned out not to be the problem.
72 Infiniium 9000 Series Oscilloscopes Service Guide