LG 37LC7D black screen cycling

[sturoc]

Hello,
Glad to have joined up here A great resource !

I've searched for this particular problem but found nothing close so here goes:

LG 37LC7D lcd tv. A freebie.

Problem: upon turning on after 5 green blinks power light goes solid green TV powers on and screen comes up but after a few seconds blacks out then comes back up and blacks out again. it is totally black with no backlight 'ghosting' . Power light remains solid green.
This continues at regular intervals every 2-3 seconds while powered on.

Signal is getting to the tv since I can see whatever is connected/selected to it in those few seconds. Menu is accessible but visible only when screen comes up for those few seconds each time.

So I started off by replacing the PSU caps that were bulging badly even the ones not indicating failing. There were several that I did not replace since the caps kit I bought did not supply them and it was noted I didnt need to unless signs of obvious failure was present ( the dreaded bulging).

Once replacement was complete i fired it up and it still has the same problem stated above.

Any recommendations as to my next step in troubleshooting ?

[vinceroger69]

Re: LG 37LC7D black screen cycling

can you take a clear picture of how the boards are all connected in your set also one of each of the board and include the board numbers then the best place to start is too take voltage readings on the power supply and make sure they are correct also a capacitor does not have too be bulged to of failed it can also fail because of high esr

service manual attached

[sturoc]

Re: LG 37LC7D black screen cycling

thanks for the quik reply & link !
Will get a photo posted later this afternoon (pacific time USA).
I did consider that a bulging cap is not the only indicators of failure. As mentioned there are 2-3 that were not replaced since the kit did not include these, Id o have a multimeter to test voltages etc.
Will be updating later.

[sturoc]

Re: LG 37LC7D black screen cycling

Attch'd are the pics of rear panel
Those covered boards will take a minute to get into will post pics in a bit

Is there a separate inverter PCB in this design ?

PSU is EAX 32268301/8

06/12/12 rev 1.0

[vinceroger69]

Re: LG 37LC7D black screen cycling

top right of the psu under the metal cover is the tcon board and under the large shield too the right of the psu is the main board what you really need to do is turn the tv on and take dc volt readings of the two grey wire connectors on the psu if you can write down the dc volts and any writing by the side of that pin your testing ie 5v - 5vstby etc that way we can see what voltages are missing if any.

[dick_barton]

Re: LG 37LC7D black screen cycling

You can also check all the solder joints of the transformer shown bottom left hand side of picture 1 where the pink high tension cable is. These can have poor joints over time.
Also check that the pink cable has not been cut/scuffed where it touches the metal panel.

[sturoc]

Re: LG 37LC7D black screen cycling

Appreciate the tips, Will ck and post back shortly

[sturoc]

Re: LG 37LC7D black screen cycling

Upon cking all multi pin connectors prior to MM testing of voltages, one of two on the lower left side of PSU bd was loose and after re-seating several times for a solid connect I powered TV on and viola ! A fully operational LG .

I thank you guys for quik replies and pointed troubleshooting guidance.