Keysight Technologies Infiniium 90000A Series, Service Manual

Page: 61 / 136

Troubleshooting
4
90000 A-Series Service Guide 61
• If the oscilloscope stays on after you reset the shutdown logic (by removing AC
power for 30 seconds) and powered it back on, then you have fixed the
shutdown problem.
• If the oscilloscope shuts down again after you have replaced the trigger ICs fan,
then the problem could be that the rotation sensor for all the fans located on
the backplane assembly failed, so replace the backplane assembly and redo
this part of the diagnostic test.
If the oscilloscope does not shut down after you replace the trigger ICs fan and the
backplane assembly, you have fixed the problem. Replace any case fans that were
not working.
If the oscilloscope still shuts down, follow these steps:
1
Replace all the case fans and verify that they work properly.
2
Reset the logic by removing AC power for 30 seconds and make all of the case
fans so they cannot rotate. For example, have two people hold the four fan hubs
or insert an object between the blades of each of the fans.
3
Power the oscilloscope back on. If it shuts down again, the fan sensing and
shutdown function is operating properly.
If the oscilloscope shuts down and the TEMP FAIL indicator LED is on, then one of
the scope channels is getting too hot or the temperature sensing circuitry has
failed. Normally, you would have to turn the instrument on and leave it on for a
while before you would see a shutdown due to temperature. If all the fans are
turning, it is unlikely that the unit would shut down due to temperature unless the
airflow is being restricted or the input air is already too hot to cool the insides of
the oscilloscope. If one or more of the case fans has failed, the unit would overheat
and shut down, but the oscilloscope would alert the user that one or more case
fans has failed and the unit needs to be repaired.
It is possible that all the case fans and the trigger ICs fan are working, but the unit
still shuts down because of temperature due to one or more of the channels
malfunctioning and drawing too much current. In this case, you would need to
replace the acquisition assemblies one at a time until you find which assembly is
defective. It is also possible for one of the heat sinks on one of the acquisition
assemblies’ critical parts to become detached and cause that part to overheat and
shut down the instrument.
WARNING
INJURY CAN RESULT! The following procedure requires you to touch fan hubs with
objects or to use objects to stop the fan blades from moving. Use caution when
working near the fan blades with the cover removed from the oscilloscope. The
cooling fan blades are exposed on one side and can be hazardous. Be careful not to
let the moving fan blades come in contact with any part of your body.