76FW-53H (serv.man13). DA100 and DW100 training course notes - Sharp TV Service Manual (repair manual). Page 11

Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 8

At switch on C362 is discharged holding IC301, pin 12 low preventing any output from IC301 until
supply has been established. Once supply has been established and IC301, pin 12 is greater than 4v
then the IC301 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 CTV to standby mode.

During system reset or when the ‘Line Mute (HOUT)’ is present, the audio outputs will be muted due
to an increase in Q305 base bias, turning it on.

The circuit description/diagram for this mute signal is shown on page 19.

-

+

PRE

-

+

PWM

16

14

7,13

12

6

4

5

15

17

1,2,3,18,19,20

9

10

8

11

N.C

Vcc pow

Vcc sign

Boot

Boot Diode

Vref

-Vcc

-Vcc

Freq

Sign-GND

St-By/Mute

Feedcap

TDA7480

Mute

R362
4k7

Q305

C362
2.2

Input

R372
10k

C356
15nF

C357
1nF

R375
47k

C359
4n7

C354
100pf

R352
12k

-16v

C358
100nF

C360
560pF

R353
150

C361
470nF

Protection

C353
100nF

+16v

R351
27k

R358
100k

L352

200kHz

IC301

R350
10k

+5v