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DA100 (50Hz) Chassis – Article for Television Magazine
Protection - Microprocessor
Audio Output
The outputs from all of the audio output stages are fed to the base of Q303 and Q304. C377 and
R361 form an averaging circuit. As the output voltage fed to the speakers should have an average DC
of 0V over a period of time, the DC voltage at the base of these transistors should be zero. If this
base voltage were to increase in a positive direction Q303 will turn on, removing the bias from IC1001
pin 100, and the television will switch to standby. The same is true if the base voltage increases
negatively, this time Q304 will turn on, turning on Q302 causing IC1001 pin 100 to fall and the
television will again switch two standby.
R361 form an averaging circuit. As the output voltage fed to the speakers should have an average DC
of 0V over a period of time, the DC voltage at the base of these transistors should be zero. If this
base voltage were to increase in a positive direction Q303 will turn on, removing the bias from IC1001
pin 100, and the television will switch to standby. The same is true if the base voltage increases
negatively, this time Q304 will turn on, turning on Q302 causing IC1001 pin 100 to fall and the
television will again switch two standby.
Figure 52: Audio Protection Circuit
Beam Current
If the beam current increases, D622 will conduct due to the ABL sense pin of T601 (earth return of
the EHT over-winding) going more negative, Q606 will turn on. This will remove the bias from IC1001
pin 100 and the television will switch to standby
the EHT over-winding) going more negative, Q606 will turn on. This will remove the bias from IC1001
pin 100 and the television will switch to standby
Horizontal Mute
During the boot sequence the horizontal drive is muted by the HOUT signal from the microprocessor
(IC1001 pin 57). Its function is to remove the horizontal drive by turning on Q607, thus placing a
short between the horizontal drive signal and ground, at the same time this HOUT pulse will cause the
audio mute circuits to activate, preventing any noise from the speakers during start up and shut down.
HOUT will also occur when the microprocessor cannot communicate with the other devices connected
to the I2C buses
(IC1001 pin 57). Its function is to remove the horizontal drive by turning on Q607, thus placing a
short between the horizontal drive signal and ground, at the same time this HOUT pulse will cause the
audio mute circuits to activate, preventing any noise from the speakers during start up and shut down.
HOUT will also occur when the microprocessor cannot communicate with the other devices connected
to the I2C buses
Figure 53: Horizontal Mute Circuit
Page 52 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
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