Acer V551 (new) CRT Monitor Service Guide
Chapter 2 Circuit Operation Theory
14
Confidence and Property
(7) Brightness, V-blank, change mode blank, spot killer CKT
(a) About the cut off voltage, while the voltage, cathode to G1, over the cut off voltage, the
picture will disappear. If the cut off voltage of the CRT G Gun is set at 120V and the
black level of cathode is 55v, the picture want to show the signals higher the black level
once the G1 voltage is lower than -65V.
(b) As described above, we may using the voltage control G1 as the brightness control.
Generally the G1 control range is about 12~15V if the Raster brightness is from 0 to
1.5ft-L.
(c) Similarly, we may overlap a negative pulse of vertical duration on the G1 voltage to
prevent the vertical retrace line from showing on the picture. This is to keep the voltage
cathode to G1 over the cut off voltage during the period of vertical retrace.
(d) In order to prevent the picture occurred transiently while change mode, pull down the
G1 voltage and let the voltage cathode to G1 over CUT OFF voltage. This will make
the picture blanking
(e) While monitor turned off, the discharge speed of high voltage circuit is slow since there
is no deflection scanning , a spot which will destroy the phosphor of CRT will display on
the CKT. So the SPOT KILLER circuit will generate a negative voltage higher than CUT
OFF to the G1 to cut the beam This is to protect the CRT.
+
+
+
VR202
D206
C233
R264
R267
ZD202
ZD203
R266
R243
C219
C221
C220
Q201
R237
R236
Q202
R239
R242
R238
R244
R240
R245
R241
R233
D202
Q203
(G1ADJ)
(SHORT)
1N4148
50V
2200P
(D)
4.7K
1/4W
1M
(OPEN)
(OPEN)
(OPEN)
14K
(1%)
250V
0.22U
(EL)
50V
0.22U
(EL)
50V
10U
(EL)
H945
10K
10K
H945
4.02K
(1%)
1/2W
120K
68K
(OPEN)
(1%)
4.7K
1.8K
(1%)
33K
(FS)
1/2W
100
(OPEN)
BF423
VFB
CLBL
G1
-190V
GUARD
+50V
+5V
HUNLOCK
BLANK
BRITE