Keysight Technologies N5244/5B Service Manual page 108

Troubleshooting
Power Up Troubleshooting
To further isolate the failure in the three remaining assemblies, measure the
resistance (with the power turned off) from the power supply test points to
either ACOM or DCOM.
Make sure that the only assemblies plugged in are the four minimum
required assemblies listed above.
Check for shorts (zero Ω) or very low resistance (approximately 1 Ω). If a short
or low resistance is measured, isolate each of the remaining four boards in the
following order, and recheck the shorted test point after each board is
removed. You should be able to determine if the shorted condition has
changed.
Isolate the remaining three assemblies:
— remove the A21 CPU board
— remove the A20 power supply
— remove the A19 midplane board
— This leaves only the A18 system motherboard installed. If the resistance
measurements are still incorrect, this is the suspected faulty assembly.
If the Fans Are Not Operating
The power supply may be in thermal shutdown if the instrument has been
operating without the fans running. Allow the instrument to cool down
before troubleshooting.
If all five fans are not operating, suspect a power supply problem or a defective
A18 system motherboard. Refer to
check the individual supplies. If the supplies are within specifications, the most
probable cause is a defective A18 system motherboard. Refer to
and Replacing the A18 System Motherboard" on page
If only one or two fans are not functioning, and the power supplies are within
specifications, suspect the A18 system motherboard or defective fan(s).
Perform the following procedure.
1. Remove the fan bracket, with fans attached, from the analyzer to expose
the fan power cable connections on the A18 system motherboard. Refer to
Figure 4-3
Replacing the Fans" on page
2. Plug in the power cord and measure the fan voltages at all three
connectors on the A18 system motherboard. THIS MUST BE DONE
QUICKLY AS THE ANALYZER WILL RAPIDLY OVERHEAT WITHOUT THE
COOLING EFFECT OF THE FANS. DO NOT PLUG IN THE POWER CORD
UNTIL READY TO PERFORM MEASUREMENTS.
4-14
"Power Supply Check" on page 4-10
for location of these connections. Refer to
7-89.
7-27.
"Removing and
Keysight N5244B/45B Service Guide
to
"Removing