Servicing the Sharp DA100 (50Hz) and DA50W chassis

摘要

Previous articles in this series have covered most of the basic circuitry used in these chassis in some detail. Two sections remain, the picture-rotation and scan-velocity modulation circuits. Picture rotation Because of the width of a 16:9 CRT the picture can be tilted horizontally by external magnetic fields. An extra coil is fitted around the bowl of the CRT to overcome this problem. It is driven by a DC amplifier that's controlled by a signal from the microcontroller chip IC 1001. Fig. 51 shows the circuit. The microcontroller chip provides a PWM correction signal at pin 55. This is low-pass filtered by R1620 and C1608 and then fed to the error-amplifier chip IC 1601. The output from this IC swings between a positive and a negative voltage depending on the mark-space ratio of the PWM from IC1001.