Abl (Auto Brightness Limiting) - Sony CPD-420GS Training Manual

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ABL (Auto Brightness Limiting)

The ABL circuit is used to control the overall beam current and brightness
of the CRT. The T901/11 FBT output is rectified by D904 and filtered by
C929. As beam current increases, the voltage output from T901/11 de-
creases (current is inversely proportional to the voltage). This voltage via
D802 and D801 is input to IC805/13 (REF). When beam current be-
comes excessive and the output voltage from T901/11 decreases, the
reference voltage at IC805 pin 13 and pin 14 is decreased. As a result,
the duty cycle of the PWM output from IC805/18 is reduced and the HV
output is decreased to limit beam current and prevent CRT damage.
IC805/18 PWM