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Acer V551 (new) CRT Monitor Service Guide
Chapter 2 Circuit Operation Theory
(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.
HV
1
FOCUS
13
G2
6
+12V
11
R350
30K
12
2
D320
1N4148
R352
100K
ABL
CONT
C307
4700P
50V
(D)
+C333
R340
330
Q316
A733
1U
50V
(EL)
9
R355
10K
1/4W
R351
6.8K
10
D309
1N4148
5
VR301
20K
(ABLADJ)
3
T303
19.70060.001
8
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
13
Confidence and Property