Service Guide 5-13
8719ET/20ET/22ET Power Supply Troubleshooting
8719ES/20ES/22ES If the Green LEDs of the Post Regulator (A8) Are Not All ON
RF Network Analyzers
If the Green LEDs of the Post Regulator (A8) Are Not All
ON
The green LEDs along the top edge of the post regulator (A8) are normally on.
Flashing LEDs on A8 indicate that the shutdown circuitry on it 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.
Maintain A15W1 Cable Connection
1. Switch off the analyzer.
2. Remove A8 from its motherboard connector, but keep the A15W1 cable connected to it.
3. Short A8TP2 (AGND) (see Figure 5-3) to chassis ground with a clip lead.
4. Switch on the analyzer and observe the green LEDs on the A8.
• If any green LEDs other than +5VD are still off or flashing, continue with the next
section “Check the Post Regulator (A8) Fuses and Voltages.”
• If all LEDs are now steadily lit except for the +5VD LED, the preregulator (A15) and
post regulator (A8) are working properly and the trouble is excessive loading
somewhere after the motherboard connections at A8. Go to “Remove the Assemblies”
on page 5-14.
Check the Post Regulator (A8) Fuses and Voltages
Check the fuses along the top edge of the Post Regulator (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.)
2. Measure the voltages at A15W1P1 (see Figure 5-6) with a voltmeter having a small
probe.
3. Compare the measured voltages with those in Table 5-2.
• 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 preregulator (A15) and post regulator (A8) are working
properly and the trouble is excessive loading somewhere after the motherboard
connections at A8. Continue with the next section “Remove the Assemblies.”
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