Keysight Technologies Infiniium MSOV 084A, Service Manual

Page: 67 / 164

Troubleshooting
4
Infiniium V-Series Oscilloscopes Service Guide 67
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 unit not to 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.
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 output
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 0 ohms.
Power supply disconnect
Measuring the backplane assembly resistance b12 V and ground across Q1409