Hitachi HT-4139-28 Maintenance Manual page 33

Test-4:
Auto Calibration of Hardware (Image Distortion Check)
Read 11 "┃" marks at the top edge of the paper, displays reference values(reference coordinates) and measured
values (Sensor coordinates).
At the recognition of characters, the marks are used to correct image magnifications (distortion).
In case of failure:
(1) Understand the issue with the diagnostic results.
In case both sides are measured simultaneously, decide which side is not good and check if the sheet is not contaminated.
And try to read it several times.
(2) Check images
Get images and check if there are noise or abnormality.
(3) Clean optical systems
During the check image (2), if there is noise and/or thin spots in the image, clean the scanning mechanism.
(4) If it still failed after the cleaning, replace the scanner assembly and the MAIN_P/K_ASSY.
Contamination of the scanning mechanism and the scanner assembly might be a cause of noise and thin spots,
etc.
Test-5: Auto Calibration of Sheet Feeding Speed
Read 11 "┃" marks and detects the speed difference in the direction of paper feeding between the reference speed
and measurement results and adjusts the feeding speed.
In case of failure:
Clean the T1 roller. Ensure there are no papers jammed in the parts.
Result (+) : Feeding speed is faster than the reference speed.
--- Increased Roller diameter caused by adhered dust, etc.
Result (-) : Feeding speed is slower than the reference speed.
--- Abnormality of paper feeding, paper slip, etc.
-H8-5-