Oki LP-1040 Maintenance Manual page 280

6.
Enter the engine maintenance mode and
make the LED head light up.
In Engine Maintenance Mode, select
Adjustment -> Engine Adjustment -> Test
-> LED-HEAD ON -> Start.
7.
The central part of the LED head lights red for
several seconds. Check visually that the LED
head lights up.
Confirm that the LED head lights up entirely.
8.
Replace the LED head back into the Printer.
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Chapter 7 - Printer Image Quality Problems Troubleshooting
LED head
Lit LED head