Block Diagram; Circuit Descriptions; Preamplifier [Lm1282]; Crt Driver [Lm2405] - Acer 7299sl Service Manual

2.4.3. Block Diagram

D-Sub Input
M101

2.5 Circuit Descriptions

2.5.1 Preamplifier [LM1282]

The IC101, LM1282, is a high bandwidth preamplifier with OSD mixer. When CUT (OSD select)
signal is low, video inputs are selected; when CUT signal is high, OSD inputs are selected.
The CONTRAST (and ABL) voltage controls the gain of three guns simultaneously. The R, G, B
DRIVE voltage controls the gain of these three guns individually to approach the white balance of
CRT.
The HCLAMP signal is used to fix the black level of video signals after AC couple. This is DC
Restoration of the preamplifier.
The HBNK signal that is active low is used to pull the LM1282 outputs below 0.2V during non-
display period.

2.5.2 CRT Driver [LM2405]

The IC102, LM2405, contains three wide-bandwidth cascode amplifiers. The parasitic capacitance and
inductance between IC102 outputs and cathodes will also influence frequency response of IC102.
The diodes and series resistors between cathodes and IC102 output pins are used to protect IC102
during tube arcing.
2.5.3 Buffer [Q111,Q131,Q151]
There are two loads for IC101, one is IC102, another is IC1902. In order to minimize the loading effect
on IC101, three emitter followers are inserted between IC101 and IC1901.
2-22
R,G,B Drive
Contrast (ABL)
R
Preamplifier
G
R,G,B IC101
B
LM1282N
H,V
H
(to Main BD)
V
Fig. 1 Block Diagram of 7299SL Video
API Confidential
No Copy/Reproduction Allowed
Auto
Buffer
Calibration
Q111
IC1902
Q131
AP3113
Q151
CRT Driver
IC102 R,G,B output
LM2405
DC Restoration
Q121,Q122
R,G,B Bias
Q141,Q142
Q161,Q162
19"
Hitachi
(Philips)
CRT
7299sl Service Guided