Genius 2093 User Manual

9

10

11

12

13

Retrace

Booster

GND

Boost

Drive

Vert.

Out

Thermal Protection

LA7838

Vertical

Deflection

377

603

601

607

4.7

Ω

610

3.3

Ω

608

4.7

Ω

609

606

602

380

470uF

605

1.2

Ω

604

611

FR205

TIP31A

+24V

+

TIP31A

TIP32A

FR205

382

1N4007

8

+24V

PCB View;
Foil Side.

The output of the LA7838 is connected to the yoke by a 3.3

Ω

 resister at 

  

610

  . It also drives the

bases of transistors  

601

  and  

603

  through 4.7

Ω

  stabilization resistors.  When the voltage drop

across resistor   

610

  reaches ±.7V the respective transistor (601 for -.7V & 603 for +.7V) takes

over most of the additional vertical yoke drive current.

Monitors with vertical deflection current which exceeds
2.2 Ap-p cannot be driven directly by the LA7838 vertical
deflection IC.   The vertical booster amplifier circuit
reduces the output current of the LA7838 by amplifying
the vertical deflection current.    The LA7838 is mounted
on the vertical booster amplifier circuit board to allow the
boosters circuit to be inserted at the output of the LA7838.

Vertical Booster Amplifier Circuit, Circuit And Function Description.

Vertical Booster Circuit,
Operation.   The following
waveforms are taken from
the 2793-VGA monitor.
See waveform #1 for the
vertical deflection current.
Waveform #2 shows the
LA7838 output current.
Waveform #3 shows the
current supplied by the
vertical booster amplifier
circuit.   These current
waveforms describe how the
vertical booster circuit
reduces the LA7838 output
current to a current which is
well within the specification
of the IC.

Vertical yoke drive, voltage waveform.

Vertical yoke drive, current waveform.

LA7838 output, current waveform.

44Vp-p

3.0Ap-p

0.6Ap-p

2.4Ap-p

Vertical booster, current waveform.

#1

#3

#2

#2

#3

#1

YC1

YC2

449

2,200uF

385

.68

Ω

+

Vertical 

Deflection 

Yoke

The retrace booster pulse, from the LA7838 pin 9, is connected to the retrace booster capacitor at

380

   and is also buffered by an NPN transistor at  

602

 .   The output of the retrace boost is

connected to the LA7838 at pin 13 and to the vertical booster NPN transistor at  

603

  .

Diodes   

604

 

 and   

611

 

  conduct current, right at the start of retrace.  This current is produced by

the energy in the yoke, from the end of the last trace.   Diode  

382

  supplies the deflection current

to both the LA7838 and the booster amplifier circuits during trace time.

Stabilization capacitors   

606

  and  

609

  are not used at present, but may be needed with other

output transistors.

610

601

603

610

380

604

382

603

602

611

606

609

87