Technical data

Troubleshooting 4
4000 X-Series Oscilloscopes Service Guide 95
To check the display supplies
This procedure checks the display supply voltages on the
system board test points when the display backlight power
cable and the display cable are disconnected.
If one or both of these voltages are bad when the cables are
connected but good when the cables are disconnected, it
indicates problems with the display assembly.
1 Follow the instructions in “To prepare for internal
assembly troubleshooting” on page 83.
2 Connect the negative lead of the multimeter to a ground
point on the oscilloscope.
3 With the power cord disconnected:
a Disconnect the display backlight power cable from the
system board connector J3303.
b Disconnect the display cable from the system board
connector J2000.
4 Connect the power cord, and turn on the oscilloscope.
5 Check the display supplies:
Test Point
(near J3303)
Expected Value Assemblies
Supplied
If Good If Bad
VP25V
(BL SUPPLY)
+24.84 V to
+25.2 V
Display
Backlight
Power
Replace the display assembly. Replace the system board.