HP LaserJet 4250 Service Manual - Page 134
Lifter-driver operation, Paper-handling, Alphabetical, printer, messages, Numerical
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The tray 2 cassette can detect the media size by using the switches described; however, the user can define the media size for the tray by using the control panel (see Paper-handling menu). In this case, the printer might not detect the media size correctly if the size that the user defined does not match the tray settings. To prevent a false size-detection, the printer measures the time it takes for the media to pass through the printer and determines the size of media that was fed from the tray. When the measured size differs from the user defined size or from the media size-switches, a message appears on the control-panel display (see Alphabetical printer messages). Lifter-driver operation The lifter driver keeps the tray 2 media-stack surface at a specific level in order to have a stabilized pickup operation regardless of the size of the media in the tray 2 cassette. The dc controller PCA operates the lifter-driver motor (M103) for 50 seconds. The motor stops when the paper-stackposition sensor (PS107) detects the media. If the paper-stack-position sensor does not detect any media within 8 seconds after the lifting operation has begun, the dc controller PCA determines that a lifter-driver motor failure has occurred, and a message appears on the control-panel display (see Alphabetical printer messages or Numerical printer messages). The dc controller PCA stops the lifting operation if the paper-stack-position sensor detects that the tray 2 cassette is missing. 120 5 Theory of operation