224 Chapter4
Troubleshooting the Analyzer
Troubleshooting an Inoperative Analyzer
If the +12 Vdc is absent, do the following:
• Disconnect the analyzer from the line power.
• Remove the A8 power supply.
• Check the continuity of the A15 motherboard from pin 1 on
A15J19 to pin 8 on A15J13.
• If the continuity of the motherboard is correct, suspect a bad
connection on the D sub-connector (between pin 8 on A15J13 and
pin 8 on A8J1) or a defective power supply.
If all the A8 power-supply LEDs are off
If all the power-supply LEDs remain off, the low-power-on (LPWRON)
control line must be checked from the front-panel line switch, through
the A16 processor/video assembly and A15 Motherboard, to the A8
power supply.
1. Disconnect the analyzer line-power cord, remove the instrument
cover, and turn the instrument so its bottom side faces up.
2. Check that the line switch provides the correct LPWRON signal at
pin 2 on A16J9.
• LPWRON becomes TTL low when the line switch is on. The
closed switch connects A16J9 pin 2 to the digital common-ground
(DCOM) through the W1 wiring harness.
• LPWRON is pulled TTL high by the power supply when the line
switch is in STANDBY.
3. Check the continuity of the LPWRON signal trace from pin 2 on
A16J9 to pin 19 on A15J13. Refer to Figure 4-2 for the pin
designations of the A15J13 connector.
4. Refer to “A15 Motherboard Assembly” in Chapter 5 for the
connector-pin designations of the A16 and A15 assemblies.
5. If the LPWRON signal path from the previous step is correct,
suspect a bad connection on the D sub-connector (between pin 19 on
A15J13 and pin 19 on A8J1) or a defective power supply. Isolate the
failure to the power supply by substituting another power supply
assembly into the analyzer.
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