Motherboard Verification - Agilent Technologies Infiniium 90000 A Service Manual

Chapter 4: Troubleshooting

Motherboard Verification

Motherboard Verification

If you have been through the Power Supply Trouble Isolation 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.
First remove the handle, outer case, and top shield. Then turn the oscilloscope on. If the unit
beeps once after about five to ten 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 4-19). You should measure about 3.3V.
If the potential you measure is correct, but the unit still has not beeped and started to boot up,
the motherboard is defective and needs to be replaced.
Figure 4-19
If the potential you measure is not correct, shut the oscilloscope down and unplug the AC cord
from the rear of the instrument. Then unplug the front panel power cable (see Figure 4-6), the
two large power cables that go to the motherboard (power harness: J1201 and J1202 - see Figure
4-8), 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.
Plug the AC power back into the oscilloscope and turn the unit on if it does not come on
automatically. 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.
Please 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.
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