Acer V551 (new) CRT Monitor Service Guide
Chapter 2 Circuit Operation Theory
13
Confidence and Property
(6) ABL CKT: (Auto Brightness Limit)
ABL is a protection circuit. When the anode current goes higher than the setting value
of ABL circuit . ABL will pull down the voltage of contrast to limit the anode current. This
is helpful to protect CRT.
10
2
G2
HV
FOCUS
8
3
9
5
6
1
12
11
+
13
R340
D320
Q316
C307
R352
R355
T303
R351
R350
VR301
C333
D309
330
1N4148
A733
4700P
50V
(D)
100K
1/4W
10K
19.70060.001
6.8K
30K
(ABLADJ)
20K
50V
1U
(EL)
1N4148
ABL
+12V
CONT
a) With crosshatch patter, FBT beam current is smaller. It makes the voltage of C333 higher
than Vcontrast Q316, is OFF the Vconstrast is freely controlled.
b) With the full white, FBT beam current rises, the voltage of C333 is down. It makes Q316
ON. Vce of Q316 is fixed