22 E8257D/67D, E8663D PSG Signal Generators Service Guide
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 30.
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 Table
1-2. Refer to the illustration in “Self–Tests 11xx: A18 CPU Self–Test
Errors” on page 76 for LED locations.
3. If the voltages are present on connector P222, turn power off and remove
the A18 CPU.
If it is determined that the A18 CPU is defective but still functions, it is
recommended that you back up the calibration data in the CPU prior to replacing
it. To back up the calibration data, see “CPU Data Backup” on page 24.
Table 1-2
Connector P222
(A31 Motherboard)
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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