Hughes JVC 220, Service Manual

Page: 43 / 140

Chapter 2---System Description
G1 Regulator for three CRTs
The input supply for the G1 grid of the CRTs is G1_SUPPLY and
is about -200V. The VAB regulates this supply to about -80V to -
30V. This supply can be adjusted by the G1_BIAS line. This
adjustment provides the brightness control function. The G1_BIAS
signal is an input of the VAB and is generated by the Video
Processor Board. In the event of a failure, such as lack of
deflection (a high on the /SWEEP_OK line), this output goes to the
most negative value of the input supply (about -200V).
G2 Regulator and black level adjustment for CRTs
The VAB also regulates the G2 grid of the CRTs. The supply for
the G2 grids (about 1200V) is generated by the HVPS. This
G2_SUPPLY is an input to the VAB. There are also three control
inputs (RED_G2, GRN_G2, and BLU_G2). The G2 voltage of
each CRT is adjusted individually by using these control lines.
This adjustment provides black level control. The G2 output
voltages are pulled down during shutdown mode.
RED_VIDEO
GRN_VIDEO
BLU_VIDEO
BLANKING
G1 SUPPLY
G1 BIAS
RESTORE
ARC_GND
BLU_CATHODE 8
BLU_GRID1 9
BLU_GRID2 10
BLU_BEAM 16
BLU_HEAT- 7
B 6
ARC_GND 3
GRN _CATHODE 8
GRN _GRID1 9
GRN _GRID2 10
GRN_BEAM 14
GRN _HEAT- 7
GRN _HEAT+ 6
ARC_GND 3
RED _CATHODE 8
RED _GRID1
9
RED _GRID2 10
RED_BEAM 12
RED _HEAT- 7
RED _HEAT+ 6
ARC _GND 3
2
4
6
23
21
1
2
13 GRN_G2
15 BLU_G2
1 G2 SUPPLY
11 RED_G2
19 /SWEEP_OK
3 + 8OV
7 + 15V
5 + 6.2V
9 -15V
/VA_OK 18
J83
J68
J68
J85
J87
J68
J68
J84-1,
J86-1,
J88-1
J67
J68
J69
J68
From
VPB
From VPB
From HVPS
From RTG
From VPB
From
VPB
From HVPS
From HVDB
From
LVPS
To VPB
To RED
CRT
To VPB
To GRN
CRT
To VPB
To BLU
CRT
To VPB
To
HVPS
VIDEO
AMPLIFIER
BOARD
Figure 2-11 . Video Amplifier PCB, Block Diagram.
Model 220 Service Manual 2-29