LG 42LE2R with the '2 seconds to black'

[lagosta]

Hi all,
I have an LCD TV LG 42LE2R with the '2 seconds to black' issue.
When I first opened it I noticed some pregnant 2200uF capacitors on the Power supply board and I immediately replaced them:


But everything remained the same, so I started debugging.

On the Power supply board we have 2 connectors, one for each Inverter board (Master and slave), checking the voltage everything looks fine

24 Volts on all 24V pins, 2.7V on 'Bri' and 4.76V on 'Inv' when TV turned ON.

Next step was to check the Inverter Boards.



I found the thread for debugging this issue:
https://www.badcaps.net/forum/showthread.php?t=10419

I did the flashlight test and I can see the image on the screen.

Then I tried disconnecting the left CCFL (close to slave inverter) and TV does the same 2 second to black but only the right side of the screen is lit.
Now when I connected back the left CCFL, the left side doesn't turn on at all. I don't know what is going on with this TV. I already checked and all cables on the Slave inverter board are connected properly.

Can I get some guidance from you guys?

Thanks

[nomoresonys]

Re: LG 42LE2R with the '2 seconds to black'

maybe if you have not, check the transistors on those balancer boards, Q15, Q18 etc, and check the little ceramic caps for shorts or low ohms.

[lagosta]

Re: LG 42LE2R with the '2 seconds to black'

The Mosfets on the inverter boards are FDD8447L and they all read arround 3.5MOhm from S to D and G to D. From S to G they read 10kOhm.
I actually already replaced the ones on Master inverter board with new ones and keep getting same values Q15, Q14, Q18 and Q19.


Regarding the capacitors, you mean C15 and C19? When I start measuring them they are in the order of 200kOhm and start increasing until Mega Ohms.
In circut they measure 19uF (parallel).


Regarding the C16,C18,C1 and C62 they also look fine in the 950uF.

[nomoresonys]

Re: LG 42LE2R with the '2 seconds to black'

wonder if you still have a bad cap or 2 on the powerboard, are you getting the boosted around 390 volts on the big filter caps with tv powered on? measured with probe on each leg. be careful HIGH voltage on primary/hot side of board. Yours may be different, ours is 120 volts coming from the wall.

[lagosta]

Re: LG 42LE2R with the '2 seconds to black'

Hi,
You mean the main power board or the inverter boards?
The main power board has 2 connectors for the inverter boards with proper 24v when TV is ON. I don't think it's damaged.

[nomoresonys]

Re: LG 42LE2R with the '2 seconds to black'

Not sure about this tv, but you can try, unhook cable from powerboard to mainboard, plug power cord into powerboard, see if backlights come on and stay on, it may not work, might have to jumper the powerboard if not.

[nomoresonys]

Re: LG 42LE2R with the '2 seconds to black'

seems like a problem with either the backlights or a backlight connection or one of the inverter/balancer boards.

[lagosta]

Re: LG 42LE2R with the '2 seconds to black'

Not sure about this tv, but you can try, unhook cable from powerboard to mainboard, plug power cord into powerboard, see if backlights come on and stay on, it may not work, might have to jumper the powerboard if not.

When I unplug the cables from Power board to main board the TV doesn't respond, the status LED is not comming up and even the relay on powerboard is not activated. When I plug it back you hear the relay on powerboard activating and TV goes into standby mode.

seems like a problem with either the backlights or a backlight connection or one of the inverter/balancer boards.

I assume it's either the backlights with a problem or the inverter boards.
On the inverter boards I already replaced the mosfets Q14,Q15,Q18 and Q19, I checked a lot of SMD capacitors and the 2 electrolytic caps and all looks fine, I just didn't test the transformers.
How can I test the transformers with a Multimeter? I can't find a schematic so I don't know witch pins connect where.


If I want to test the lamps, can I go with a 8W CFL? Like explained here:
https://www.badcaps.net/forum/showthread.php?t=19987