The operation manual is available for free download from Samsung at this site:
http://downloadcenter.samsung.com/content/UM/200305/20030529145700437_MW5592.pdf
The answer to how to lock and unlock is on page 15 of the manual. It's instructions are:
1. Press the '0' button, the display will show:
"PRESS 1- DEMO 2-CHILD LOCK"
2. Press the "2" button, the display will show:
"PRESS START"
3. Press the start button and the display will show "LOCK" then returns to the time of day.
At this point the microwave can't be used. To unlock, just repeat steps 1-3.
Hope this helps
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