1-4
Troubleshooting
A18 CPU Turn–On Test
A18 CPU Turn–On Test
At turn–on, the A18 CPU is designed to complete a series of operational checks. If all power supply
voltages are present and the A18 CPU is working correctly, the operational checks are completed.
Errors are reported if the A18 CPU has problems identifying other assemblies or communicating
with the backup memory located on the A31 Motherboard.
Failure Symptoms
• display is not functioning
• CPU fails to complete the turn–on check and does not reach normal LCD operation
• display is not functioning after turn–on
• unable to control signal generator from front panel
• error message is displayed after turn–on
A2 Display Not Functioning or A2 Display Not Functioning After Turn–on
Refer to “Front Panel Display Assembly Troubleshooting” on page 1-11.
A18 CPU Fails to Complete the Turn–On Check
1. Turn power off and remove outer and inner covers.
2. Turn on power and verify A18 CPU LED DS9 (+3.4 Vdc) and DS10 (+5.2 Vdc) are on. If either of
the LEDs are off, check the voltages in Table1-2.
3. If the voltages are present on connector P222, turn power off and remove the A18 CPU.
4. Inspect the pins on the A31 Motherboard connector. If the pins look good replace the A18 CPU.
5. If either of the voltages are missing, refer to “Power Supply Troubleshooting” on page 1-17.
6. If DS9 and DS10 are on, proceed to “Checking the A18 CPU Voltages” on page 1-5.
Table 1-2
Connector P222 Supply Voltage Acceptable Range
Pin 45-48, 95-98 +3.4 Vdc +3.4 ± 0.07 Vdc
Pin 49, 50, 99, 100 +5.2 Vdc +5.2 ± 0.1 Vdc
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