Pwr - LG 32LG40 Training Manual

CIRCUIT DeSCRIPTIONS
POwER SUPPlY TEST
To test everything but the backlights.
Disconnect the P2 connector from the
Main board. With the Power Supply
disconnected from other boards and AC
applied, confirm that the Power Supply
is producing 5V from either pins 9, 10, 1 1 or 12. If not, check the fuse. If the fuse is ok
and there's no 5V, replace the Power Supply. If 5V is ok then continue.
Remove AC power when adding the jumpers shown in the image. Apply power when making
the test. Short either pins 9, 10, 1 1 or 12 (5V) to pin 19 (PWR) using a 10K resistor.
This turns on the power supply. Confirm that the other low voltage power supplies are
activated. Pins 1 and 2 should be 16V. Pins 5 and 6 should be 12V. Pin 18 (AC Detect)
should go high.
BACklIGhT TEST
If the 1st test was successful, continue.
Remove the power, leave the original
10K in place, and add a jumper between
pin pin 19 (PWR) to pin 20 (INV). Apply
AC Power to the board and observe the
4
Backlights. If normal, the backlights should turn on and off 4 times then go off.
If only 1/2 the backlights light (right side or left side), confirm the connectors are ok.
2
Check the Transformer left and right center pins for a signal. If ok, the panel is defective
due to a backlight failure. If the pulse is missing on one side (L or R center legs) of the
transformer, the power supply is defective.
L
If there is no backlight activity, confirm the Fuse F700 has approx. 300V on both sides.
If only on one side, check fuse for open. If there is no 300V, replace the Power Supply.
G
If 300V DC is present, observe the L and R center legs on the left hand side of ballast
transformer T701. Look for 58Khz pulse at 8.7V p/p. If yes, confirm the connectors to
backlight are ok. If ok, then the panel is defective. If no pulse is found, replace the Power
6
Supply.
BACklIGhT vOlTAGES
0
P401 and P402 Backlights
Pin STBY
1
2
48 48
Fall 2008 LCD Training Fall 2008 LCD Training
Run Diode Check
0V >1Kac
0V >1Kac
24 22 20 18
23 21 19 17

PWR

INV
24 22 20 18
24 22 20 18
23 21 19 17
PWR
23 21 19 17
PWR
INV
24 22 20 18
23 21 19 17
PWR
Caution backlight peak-to-peak over
1KV (Freq. 54Khz). Pins 1 and 2 are
actually shorted together (Either
plug). Reading between P401 and
0V
P402 reads the Transformer T701
0V
(0.1V).
16 14 12 10 8 6
15 13 11 9 7 5
+5V
10K
16 14 12 10 8 6
16 14 12 10 8 6
15 13 11 9 7 5
15 13 11 9 7 5
+5V
+5V
10K
10K
16 14 12 10 8 6
15 13 11 9 7 5
+5V
10K
4 2
P2
3 1
4 2
P2
4 2
3 1
P2
3 1
4 2
P2
3 1