Chapter 5 5-13
Power Supply Troubleshooting
If the Green LEDs of the A8 Are Not All ON
If the Green LEDs of the A8 Are Not All ON
The green LEDs along the top edge of the A8 post regulator are normally on.
Flashing LEDs on A8 indicate that the shutdown circuitry on the A8 post regulator is
protecting power supplies from overcurrent conditions by repeatedly shutting them down.
This may be caused by supply loading on A8 or on any other assembly in the analyzer.
Remove A8, Maintain A15W1 Cable Connection
1. Switch off the analyzer.
2. Remove A8 from its motherboard connector, but keep the A15W1 cable connected to A8.
3. Remove the display power cable.
4. Short A8TP2 (AGND) (see Figure 5-3 on page 5-6) to chassis ground with a clip lead.
5. Switch on the analyzer and observe the green LEDs on A8.
• If any green LEDs other than +5 VD are still off or flashing, continue to “Check the
A8 Fuses and Voltages” on page 5-13.
• If all LEDs are now on steadily except for the +5 VD LED, the A15 preregulator and
A8 post regulator are working properly and the trouble is excessive loading
somewhere after the motherboard connections at A8. Continue to “Remove the
Assemblies” on page 5-13.
Check the A8 Fuses and Voltages
Check the fuses along the top edge of A8. If any A8 fuse has burned out, replace it. If it
burns out again when power is applied to the analyzer, A8 or A15 is faulty. Determine
which assembly has failed as follows.
1. Remove the A15W1 cable at A8. (See Figure 5-5 on page 5-9.)
2. Measure the voltages at A15W1P1 (see Figure 5-6 on page 5-11) with a voltmeter
having a small probe.
3. Compare the measured voltages with those in Table 5-2 on page 5-10.
• If the voltages are within tolerance, replace A8.
• If the voltages are not within tolerance, replace A15.
If the green LEDs are now on, the A15 preregulator and A8 post regulator are working
properly and the trouble is excessive loading somewhere after the motherboard
connections at A8. Continue to “Remove the Assemblies,” next.
Remove the Assemblies
1. Switch off the analyzer.
2. Install A8. Remove the jumper from A8TP2 (AGND) to chassis ground.
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