59ES-D7H (serv.man3). DA100 and DW100 training course notes - Sharp TV Service Manual (repair manual). Page 18

Colour Television – DA100/DW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

September 99

Page 15

As in previous chassis a transformer-less driver circuit has been used, with the driver stage obtaining
it’s run voltage from the fly-back transformer, T601.
At switch on +8v from the power supply is applied to Q603 collector via R605 and Q602 collector via
R628 and R608. At the same time –16v is applied to Q602 emitter via R619. Horizontal drive from
IC801 is applied to the base of Q603, This will cause Q603 to switch, which in turn switches the line
output transistor Q601, producing an e.m.f on pins 6 and 10 of the fly-back transformer T601. The
e.m.f at pin 10 is rectified by D611 to produce the positive run voltage and the e.m.f at pin 6 is
rectified by D610 to produce the negative run voltage.

With this type of driver circuit, it is essential that the circuit is started softly, otherwise transient pulses
can damage the line output transistor. This is achieved by doubling the horizontal drive frequency;
which effectively reduces Q601 on time, until the run voltage has been established.

In addition to producing the EHT, focus, screen voltage and horizontal scan from the fly-back
transformer T601, the +/-13v rails for the field output are produced at pins 5 and 9. D609 rectifies the
e.m.f at pin 9 producing the +13v and D608 rectifies the e.m.f at pin 5 producing the –13v.

Horizontal fly-back pulses (HFB) from pin 1 is fed to IC801 for both timing purposes and safety
(prevents excesses EHT), HFB is also rectified by D610 to produce +25v for vertical fly-back. From
the primary winding (pin 7) the HT is stepped up and rectified by D621 to produce the HT required by
the CRT drive circuit. Finally a negative going voltage is fed from pin 8 to the protection circuit. This
voltage represents the beam current. The greater the beam current (Bright Raster) the greater this
voltage would be in a negative direction. This negative voltage is then fed to the IC1001 pin 95 via
D622 and Q606. Once this voltage has exceeded safe working levels IC1001 pin 95 will go low
switching the CTV to standby.

EHT

East/West Circuit

+8V

-16v

Q601

Line
Drive

D610

Focus

Screen

ABL

HFB

+25v

+13v

-13v

10

1

9

5

6

8

13

+150v
(CRT Base)

+150v

2

7

3

4

F602

F601

D609

D608

D510

R617
22

R624
5R6

D604

D603

C601
12nF

C610
27nF

L609

R612
22

C607
330

R619
560

R642
470

R601
3k9

Q602

Q603

R605
470

R607
12k

R628
1k

R608
1k

L606

D611

R623
1

R617
22

D621