Service manual

5 121
Power Supply Troubleshooting
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5. Power Supply Troubleshooting
A50 Shutdown LED
The A50 SHUTDOWN LED turning off indicates some of A50 power supply is shut down
by the A50 shutdown circuitry.
There are two FAN conditions, rotating and not rotating when the SHUTDOWN LED turns
off. When the fan is rotating, the shutdown circuit is probably activated by the over current
condition on the power lines in the A50 DC-DC Converter. In this condition, though the
A50 power supplies, +5 VD, +15 V, -15 V, +8 V, and -8 V are shut down, the Fan Power
+24 V is still supplied to the fan. When the fan is not rotating, the shutdown circuit is
probably activated by the FAN LOCK signal missing.
NOTE Once the A50 shutdown circuit is activated, the only way to reset the circuit is by turning
the analyzer power off. Wait a minute after turning the analyzer off. Then turn it on.
3.Check the A50 Five LEDs
1. Turn the analyzer power on.
2. Look at the A50 Five LEDs. The LEDs are normally on. The Five LEDs locations on
the A50 DC-DC Converter is shown in
Figure 5-2.
• If one or more LEDs are off, continue with the Troubleshoot the A50 DC-DC
Converter section in this chapter.
• If the A50 Five LEDs are correctly on, continue with the next step, Check the A1
+5 VD LED.
4. Check the A1 +5 VD LED
1. Remove the analyzer's bottom cover.
2. Turn the analyzer power on.
3. Look at the +5 VD LED. The +5 VD LED location on A1 CPU is shown in Figure 5-3.
The LED is normally on.
• If the +5 VD LED is off, continue with the FIND OUT WHY THE A1 +5 VD LED
IS NOT ON STEADILY section in this chapter.
• If the +5 VD LED is on, the +5 VD power supply is verified with 95% confidence
level. If you want to confirm the last 5% uncertainty, perform steps in the next step,
Measure the A1 +5 VD Voltage.