Quick Method for Repairing Scanners
There are several key points in repairing scanners. The parts that are most susceptible to damage during scanning include the power adjustment transistor, line tube, variable potentiometer, a few capacitors on the field, and current-limiting resistors. For example, when there is no capacity on the upper edge of the scroll C411, C413 or R425 breaks, the lower edge scroll indicates that the field width potentiometer is damaged. When encountering difficult or strange faults, adjust those variable resistors first to see if there are any changes, which can help determine whether the fault lies with the variable resistor. Image shaking generally indicates that the large filter capacitor or adjustment transistor has broken down. Excessive brightness sometimes accompanied by retrace lines may be due to R316 breaking or Q104 breakdown. If the image size cannot be adjusted, it could be due to issues with Q901, Q902, Q903 or ZD901. A horizontal bright line may result from R315 breaking, IC, ZD401 breakdown, or a pair of transistors being faulty. A vertical bright line may be caused by poor soldering or failure of C315. If the image shakes as the program runs, it suggests aging of the four rectifier tubes. Narrow field amplitude with linear distortion may be due to C406 having no capacity. White light without an image could be due to Q104 or the brightness potentiometer. If the image expands or contracts as the brightness increases, it indicates that the capacitor next to the line transformer has failed. Half of the display being dark might be due to a 180V filter capacitor failure.
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