Product specifications

DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 43 of 80
Audio
On Board Circuit Operation
At switch on C362 is discharged holding IC301, pin 12 low preventing any output until supply has been
established. Once supply has been established and pin 12 is greater than 2.7V the IC will start to oscillate,
producing a PWM signal with a frequency and a mark space ratio which is dependant on the input signal at pin 11.
L352 and C361 form a low pass filter for conversion of the PWM signal into an analogue signal to drive the
loudspeaker. A proportion of this drive signal is fed into an averaging circuit via R358 as a protection signal i.e. if
the average of the signal at the junction of R358 and L352 is not zero then the software will switch the
television to standby mode.
Figure 42: Audio Amplifier Circuit (left channel)
Mute Circuit Operation
During system reset or when the ‘Horizontal Mute (HOUT) is present, the audio outputs will be muted due to an
increase in Q305 base bias, turning it on and taking pin 12 to ground.
Sharp Electronics (UK) Limited - May 2003
Revision 3