Motherboard Verification - Keysight 90000 X Series Service Manual

Motherboard Verification

If you have been through the Power Supply Troubleshooting section of this chapter and
the oscilloscope still does not stay powered up, the problem may be with the
motherboard. To diagnose this problem, follow these steps.
1 Remove the handle, outer case, and top shield.
2 Turn the oscilloscope on.
If the unit beeps once after about 5 to 10 seconds but fails to boot up, the motherboard
is defective and needs to be replaced.
If the unit fails to beep after it is powered on, then measure the potential relative to
the chassis at pin 9 of J1201 (Figure 4- 16). Pin 9 is the reset line for the motherboard.
It is controlled by the backplane. You should measure about 3.3V. If the potential you
measure is correct, but the unit still has not beeped and started up, the motherboard
is defective and needs to be replaced.
Figure 4-16 Measure potential relative to chassis at pin 9 of J1201
3 If the potential you measure is not correct, shut the oscilloscope down and unplug the
AC cord from the rear of the instrument.
4 Unplug the front panel power cable (Figure 4- 9), the two large power cables that go
to the motherboard (J1201 and J1202 as shown in Figure 4- 11), and the red and blue
SATA cables (J900 and J901) from the backplane assembly. Do not allow the two SATA
cables to touch the backplane assembly and cause a short circuit.
5 Plug the AC power back into the oscilloscope and turn the unit on if it does not come
on automatically.
6 Measure the potential relative to the chassis at pin 9 of J1201 again.
If you measure the required 3.3V, the motherboard is defective and needs to be replaced.
If you did not measure the correct voltage, the backplane assembly is defective and
must be replaced.
7 Be aware that there could be a fault on the motherboard that caused the backplane
assembly to fail so before you plug the motherboard cables back into the new backplane
assembly, measure the resistance to the chassis from the pin 9 contact in the connector
that plugs into J1201. If you measure a very low resistance or a short circuit to the
chassis, replace the motherboard and then assemble the instrument and confirm the
unit beeps and boots up properly.
Chapter 4: Troubleshooting
Motherboard Verification
67