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Troubleshooting
Troubleshooting Assembly–Level Problems
Symptom: Green front panel LED and power supply LEDs on motherboard blinking
Overvoltage or Overcurrent The individual supplies in the instrument are not fused, but an
overvoltage or overcurrent condition can shut them down. With either of these conditions, the front
panel green LED and the power supply LEDs blink at approximately 2 Hz. The power supply tries
to revive, but if the condition does not clear, the instrument stays in this mode. In some cases,
cycling power fixes the problem.
To troubleshoot, use the following steps to isolate the defective assembly:
CAUTION Remove a minimum number of assemblies at one time. If the power supply does not
have a minimum load on it, the supply voltage increases to an overvoltage condition.
1. Turn off the instrument and remove one of the assemblies biased by the faulty supply.
2. Turn the instrument on and check whether the overvoltage or overcurrent condition still exists.
If it does not, replace the assembly removed in Step 1. If it does, continue with Step 3.
3. Turn the instrument off and reinstall the assembly removed in Step 1. Remove the next
assembly and see if that fixes the problem. Continue this process until the supply functions
properly.
4. Replace the last assembly that you removed.
Thermal shutdown With thermal shutdown, the front panel green LED and the power supply
LEDs blink as long as the condition exists. There are two temperature sensing devices in the
instrument: one on the A8 Output, and one on the A19 Power Supply.
To troubleshoot:
1. If the instrument is hot, ensure that the fan is working and let the instrument cool off.
2. If the instrument still shuts down, remove the Output assembly.
3. If the instrument still shuts down, replace the power supply.
Symptom; +9, –6, or –5.2 V LEDs not on
These supplies are generated on the YIG Driver Assembly.
Troubleshoot using the Power Supply vs. Assembly Matrix that begins on page 1-17.
1. At P112 of the Motherboard, ensure the YIG Driver Assembly is receiving the +32, +15, +10, –7,
–15 Vdc supplies.
2. If the supplies are present at P112, note in the matrix where each supply is used.
3. Power down the instrument and remove one of the assemblies that is biased by the faulty supply.
4. Power the instrument up again and check the faulty supply. If it is still bad, power down and
re-install the first assembly removed.
5. Remove the next assembly and see if that fixes the problem. Continue this process until the
supply functions properly.
6. Replace the last assembly that you removed.
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