Servicing; General Information - LG RU-27FB30C Series Service Manual

GENERAL INFORMATION

Servicing the FC Narrow is the same as with other LG
single-board chassis. If the set is dead, first check the
standby and switched voltages. If the switched volt-
ages do not appear, check the power "On" circuit. If
the power supply is OK and the set will turn on, the
Horizontal sweep circuit should be checked next. Is
horizontal drive available from the video processor chip.
If the sweep system does not start up, sweep-derived
voltages will not be generated.
If the sweep and high-voltage circuits are OK and video
or audio are missing, then the audio/video/tuner cir-
cuits should be checked. If the receiver is working but
some feature is not working, check the Service Menu.
Bring up the Service menu and check to be sure that all
items are set correctly.
MODULE-LEVEL SERVICING
The FC Narrow Chassis is Module Level repair only. Re-
placement modules are available on an exchange basis.
If the CRT or Video processor IC are replaced, Black/
White tracking must be reset. Refer to the Service Menus
section of this book for Black/White tracking adjust-
ments.
When troubleshooting video circuits, remember that all
video travels through the Video/Audio switcher IC. A
defect in either of these IC's can result in no video.
SERVICING THE POWER SUPPLY
Check the standby voltages first:
+V1 at CX3406 (usually 169.7 VDC when 120 VCA)
+11VSB at CX3610
+11LSP at CX3611
+5VSB at CX3802
+3.3VSB at CX3806
+1.8VSB at CX3811
Check the following:
Keyboard input at IC100 pin 51.
IR input at IC100 pin 50.
Power On output at IC100 pin 49.
Check the switched voltages:
+V2 at CX3456
B+ (110VDC) at CX3854
+35VSW at CX3663
+33VSW at ZDX3860
+17VSW at CX3662
3828VD0210A

SERVICING

+14VSW at CX3660
+11VSW at ZDX3865
+9VSW at CX3865
+8VSW at ZDX3870
+6VSW at CX3661
+5VSW at CX3855
+3.3VSW at CX3850
SWEEP DERIVED VOLTAGES
Video B+ (190 VDC) at C422
+28VDC at C413
+14VDC at C415
-14VDC at C419
CRT FILAMENT
Check at pin 3 and 4 of connector CN2F5. This should
read voltages between 6.0 and 6.4 volts AC on a true
RMS meter.
MICRO AND VIDEO PROCESSOR IC100
Check the following key operating signals and voltages:
Horizontal drive at pin 60.
Vertical drive at pins 84, 85.
R Out IC100 pin 76.
G Out IC100 pin 72.
B Out IC100 pin 71.
Serial clock, Serial Data pins 57 and 58 respectively
3.3VSB at pins 65, 46.
1.8VSB at pins 43, 24.
VERTICAL CIRCUIT
Check the following at IC301.
Vertical drive VA at pin 7.
Vertical drive VB at pin 6.
Vertical out at pin 5.
+14VDC at pin 1.
-14VDC at pin 4.
HORIZONTAL CIRCUIT
Check the following:
Horizontal drive to base of R402 driver.
Driver transformer output at base of QX401.
Shutdown voltage at collector of Q403.
3-1
FCN - SERVICING