typical GT1790A - Display Contrast Adjustment; Key Lock Setting

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24. Adjusting the contrast
The contrast of the display on the panel can be adjusted
in five steps.
1) Call contrast adjustment screen
Select the contrast adjustment from the menu on mode
screen and press Edit key ❽ , and then screen A for
contrast adjustment value will be displayed.
2) Adjust the contrast
The contrast can be adjusted in five steps from 1 (brightest)
to 4 (darkest) by pressing Data Change key ❼ .
25. Setting the key lock
Operation of the data change key can be disabled by setting the key lock. Refer to the Service Manual
for how to invoke the key lock setting function and how to set the key lock.