LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

[high-tech]

Hello and hope you all had a decent weekend!

I got this tv in for repairs and the customer replaced the power supply with one from Tri State Modules. The old P/S board had the usual bad caps in the secondary stage. That didn't fix the problem the tv still shuts off.

The only thing I can find the first picture, the pin out shows inv control, 5th down from the top is at 3.3v with ps on, the inv comes on when that 3.3 goes low to about 1.8v to 1.6v inv comes on and flashes and the voltage goes to 0v and the process repeates three times and the TV turns itself off to standby. I can turn it right back on with out unplugging or resetting fault.

While Tv is on the sound is on and the first time backlight flashes I see the channel indicator and snow the next 2 times only snow, then it shuts down.
IDK

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

What happen if you disconnect the cables to the inverter board?

[high-tech]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

The inverter is on the P/S board. I think the main board is havin a hard time holding the inv on signal low

[kiwifino]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

i've got the same problem on philips LCD tv with LG power supply. dont know what to do next.

[selldoor]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

i've got the same problem on philips LCD tv with LG power supply. dont know what to do next.

Use the search above for your tv model and see if you can find a thread IF NOT
Start a new thread headed
Philips xxxxxxx(insert model no)backlight flashes 3 times and shuts off. ( If you mean back light and not power led)
Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say what the supposed fault** was and a bit about yourself - skills tools etc.

** start from when you plug in and say exactly what you see and hear
then press the on button and say what happens. What is the power led doing at each step. Also if known how did the fault develope. Was the set
slow at coming on when on did it flicker etc etc.

[Frank O]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Hi I'm Frank O. I've read your posting. I have the same problem. Did you get yours resolved and if you did, what did you find out? Could it have been the inverter board or the back lights? I'm trying to figure this out. Can you help?

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I have the same issue on lg 42lc7d & also looks like screen is bad dark on left 1/3 vertical.
the pcb / inverter changed now at east the inverter turns on the back lights even know its short time better than blank i guess
any one figure out if the main or t-con is causing the issue?

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I got the 1/3 screen issue fixed, left inverter unpluged. whoops!
now it still turns on & off thinking its the cfl's are bad as only 1
band showing horizontally bright the rest of the screen is darker.
could it be that th back light pulling to much is causing the shut down?

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I found a bad or blown up sm cap on the ccfl board (tb42a-6plh-r) causing the bright bulbs & may be the cause of the inverter / pcb shutting down?
trying to find this cap now marked 5kv 15j 77 any help on this cap

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

15pf 5% 5000V, you can use 6300V instead. They are ballast caps to limit current flow though the lamp, it it has leakage due to high voltage break down, the inverter will shut down to protect itself. I would check all of them out and see if more than one has resistance leakage, you can also see it has tinted of bworn on the body when it is bad.
See example:
http://s807.photobucket.com/albums/y...nt%20FLX-3210/

Replacement cap.
http://www.mouser.com/ProductDetail/...9EP3wBRvDCU%3d

[tom66]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

The ballast caps are actually used to start the lamps. When the caps fall in capacitance or become leaky, the lamps don't start. The way it starts is quite novel: the inverter pulses the transformer briefly; the transfomer secondary and capacitor form a resonant circuit, which spikes the bulb with about 2~3x nominal voltage, then the inverter operates initiates normal operation once the bulb is struck and the capacitor passes AC. (It will only attempt to strike once and will check after 2 seconds or so have elapsed.) If the capacitance falls, the output spike will drop, if the capacitors become leaky, the spike will be damped (and will also reduce.)

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

When the cap is leaky, the current through the lamp will be higher than normal, the cap is in series with the lamp. The pictures shown on my photobucket, one cap has low resistance reading, it should read open circuit, so the lamp attached to that cap was A LOT brighter than the rest, and then the inverter shutdown. Since the inverter runs at high freqauency, it uses the Xc of the cap to limit the lamp current, that is why it is very small value cap.

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

yes its what i think, now just need to find the cap to see if is the fault then will prob. be the fix to other ? here but access to parts to replace this week is not there to confirm yet thanks for the input.

[tom66]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

When the cap is leaky, the current through the lamp will be higher than normal, the cap is in series with the lamp. The pictures shown on my photobucket, one cap has low resistance reading, it should read open circuit, so the lamp attached to that cap was A LOT brighter than the rest, and then the inverter shutdown. Since the inverter runs at high freqauency, it uses the Xc of the cap to limit the lamp current, that is why it is very small value cap.

That may play a role too, but it is also used to start the lamp.

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

whats the value for this cap? it is marked like this (m) 5kv 15j 77 looks kind of like a diode 1/4" surface mount

[budm]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

see post 10

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

thanks budm missed yhat post I guess. I may have one of these lying around, back to work on it.

[jettboat]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

I replaced the cap on it, but putting it together i chipped the edge of the lcd screen now its parts !&^%$
still had two really bright ccfl's must be more bad caps but Im done with it

[ajal14]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Hi there,
I got the same problem on my LG 42LC7D. I changed all the pregnant caps on the power supply , but the screen still go flashing 3 times and off again on a stand by mode . I can hear the sound and i can see the picture during the flashes moments, any help is more appreciated

[CapacityRenewals]

Re: LG 42LC7D-UB Comes on backlight flashes 3 times and TV shut off

Anyone solve this issue of 3 flashes then off? I have a customers TV same model doing this. I changed every cap on the power supply, used the heat gun and chilling tricks and nothing. The tv stays on for about 10 min then flashes off 3 times then turns off. If i restart it right away it will flash 3 times and do it again.
Seems like something with the ccfls starting isnt working. Losing my mind.