E3, E3D, Chassis - Panasonic TV Other Service Manuals (repair manual). Page 7

7

2. 

Single ABL

Purpose :
In a normal TV the ABL operation detects the current
following to the secondary coil of the fly-back transformer
and controls the contrast. In a video projection TV,
however, the current for the secondary coil of the fly-back
transformer is measured as the total current for the three
projection tube. Therefore the current can not be controlled
even if most of the electron beams are sent though one
projection tube. For this reason the monochrome ABL
circuit detects the maximum current for each projection tube
and controls the same. We have added a circuit which
accelerates the ABL operation time, and lowers the
contrast.

Operation :
In normal ABL operation detects the current flowing to FBT
which supplies the high voltage to the three projection
tubes, as with a standard TV. This is alike MD2 chassis.
The current flowing to each projection tube is detected in
the colour output transistor emitter, and the maximum
current to each projection tube is then input to the Q7735
through D3352,D3362 and D3372.

Then output value of Q7735 is input to pin No. 5,7,9 and 11
of IC7705, these are compared with pin No. 4,6,8 and 10 of
IC7705.
Compared result is output from pin No..1,2,13 and 14 as
P0, P1, P2 and P3. P0-P3 data are input to IC7702, then
CRT current following is separated to 5 levels/ Ranks in the
IC7702 as follows.

P0

P1

P2

P3

RANK

LEVEL

H

H

H

H

A

Danger

H

H

H

L

B

I

H

H

L

L

C

I

H

L

L

L

D

I

L

L

L

L

E

Safety

Detection data is input to MPU through IIC bus line and
MPU controls the contrast to keep detection level safety.

R,G,B  OUT

Q7735

D3352,D3362,D3372

CRT-Anode

FBT

T554

Q9601

4

5

7

6

8

9

11

10

2

1

13

14

+5v

10

9

2

1

14

15

59

60

43

11

10

BCL

SDA

SCL

+

-

+

-

+

-

+

-

E10 A10

16

1

P3

P2

P1

P0

LG1/W3

8

IIC bus

Q3351

Q3361

Q3371

AB