Agilent Technologies Infiniium 90000 A Service Manual page 66

Chapter 4: Troubleshooting
Over-Temperature Fault
Once you can see the case fans, apply AC power to the instrument and turn it on if it does not
start up automatically. Visually check to see if any of the fans are not turning. If all the fans are
not turning, it is probably a problem with the high side drive circuitry for the case fans.
Figure 4-12
If any of these fans are turning then these fans are probably not the cause of your shutdown
problem (you should still replace any fans that are not turning, however). If this is the case, the
next step is to see if the FAN FAIL indicator LED is on in the upper right hand corner of the
backplane assembly (refer to the circled area in Figure 4-12 above). If this LED is illuminated
then that means the system thinks there is a fan failure. Since you have ruled out the case fans
as the root of the problem, it may be that the trigger ICs fan has failed. To check this, first reset
the logic by removing AC power for thirty seconds again. Then position yourself so you can see
the trigger ICs fan on the back plane assembly. This fan is on the bottom of the backplane and,
therefore, is somewhat hidden by the acquisition assemblies. You have to look down the
backplane board to see it from above (see Figure 4-13 below).
Figure 4-13
This picture shows the location of the trigger ICs fan from the perspective of looking down the plane of the backplane assembly
from above.
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T rigger IC s fan
on backplane
assem bly