Keysight Technologies Infiniium 90000A Series, Service Manual

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56 90000 A-Series Service Guide
4
Troubleshooting
It is also possible that there is a short circuit on the bulk +12 V supply trace
somewhere in the system, which would also cause the oscilloscope to not power
on. If so, you need to isolate the assembly that is shorted. You do not need to
remove the acquisition or backplane assemblies to perform the following steps.
1
With the power turned off, disconnect the bulk +12 V supply, but do not remove
the supply from the oscilloscope.
Power supply disconnect
2
On the backplane assembly, measure the resistance across the FET (Q1409,
located in the upper right corner of the backplane) b12 V and ground
as shown below, or measure the resistance across the bulk supply input pins on
the backplane assembly. Make sure the red lead is plugged into the HI input
and the black lead is plugged into the LO or COMMON input of the DVM. On a
good backplane assembly, you should measure about 700 ohms. If there is a
short on this board, you would measure something very near zero ohms.
Measuring the backplane resistance b12 V and ground across Q1409