Keysight Technologies Infiniium 90000A Series, Service Manual

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54 90000 A-Series Service Guide
4
Troubleshooting
Under-Voltage Fault
If the oscilloscope takes about 2 seconds to lose power as just described, the
problem is either an under-voltage fault on the backplane assembly or one of the
two acquisition assemblies, or a defective bulk 12 V power supply.
To determine which problem it is, first remove the handle, the outer oscilloscope
cover, and the inner top cover to expose the motherboard cavity and the top edges
of the backplane assembly. A series of six under-voltage indicator LEDs are
located in the upper-right corner of the backplane assembly. The other LEDs in
this section of the backplane assembly indicate over-temperature or fan problems
and are described in the “Over-temperature fault” section.
Location of under-voltage fault LEDs
Each of the six under-voltage fault LEDs is labeled.
• If only the ACQ1 SUPPLY FAIL LED is lit, replace the channels 3 and 4
acquisition assembly (upper acquisition).
• If only the ACQ2 SUPPLY FAIL LED is lit, replace the channels 1 and 2
acquisition assembly (lower acquisition).
• If BP POL FAIL, NEG SUPPLY FAIL, or FPGA SUPPLY FAIL is lit, replace the
backplane assembly.
• If only the FP SUPPLY FAIL LED is lit, go to the next section, “If the FP SUPPLY
FAIL LED is lit”.