LG 42LD490-ZB troubleshooting

[wyga]

I've got that LG 42LD490-ZB which been around here for ages waiting to be repaired at some point in free time.

Issues were:
1) Stays on logo, won't boot, cannot access menu
2) Loud pitching noise from built-in speakers & av board.

So I just took a look today again. I remember by poking around with multimeter I couldn't find anything back then and it was same today.

So I've checked some common issues and apparently plenty people used to have problems with main chip. After losing hope to find any clue I went - well lets just try the hot air with some flux.

And yeah, first issue resolved. TV goes through the boot properly, can access menu, probably HDMI will be working as well but just haven't tested yet. Actually almost saved right...

But... still there is a high pitch noise from the built-in speakers without putting any signal through, just static loud awful pitching noise.
I was hoping I will be able to find something on the speaker lines or nearest IC but nope, cannot find shorted circuit.
There is however constantly 17.0 - 17.5V on speakers without outgoing audio signal as i mentioned.

Another thing is, if i get them disconnected I can pretty much hear same noise comming out of the av board just of course way quiter as it's not "amplified" by speakers...

Any ideas what am I missing?

[diif]

Re: LG 42LD490-ZB troubleshooting

"well lets just try the hot air with some flux."

Did you aim for a reflow profile or just waft some hot air?
I'm wondering if it wasn't 100% sucesfull.

[wyga]

Re: LG 42LD490-ZB troubleshooting

Pardon me the language there. I was actually aiming to reflow it.

As I couldn't come up with any other idea I wanted to give it a go with a reflow before I close it down and wait for the part to show up somewhere.

I wouldn't be able to do full BGA reball at the moment due to lack of resources and the hot air station was pretty much the only option there.

I have to say I wasn't actually expecting any positive outcome out from that but I did took that seriously. So, I have applied quite generous amount of flux in the area of LGE3556C, took the biggest nozzle and started heating it up evenly, to make sure we are not just getting the corners warm there.

After it cooled down and fitting, to my surprise it went smoothly through the boot screen, to the DTV mode.

Actually I've done some tests by now as I still got it on the desk by the way. So from what I see all functions and ports seem to be working completely fine, we've got display and sound through hdmi ports, menu working, TV is not turning off by itself, but the most important thing is that the headphone jack seems to be working perfectly fine.

On the headphone jack there is completely no noise, no distortion, crisp and clear sound.

So it makes me wonder if there is some other failure on the board.
I have managed to find schematics for current model and I did track down the circuit from NTP-7100 to speaker port but I cannot find any anomaly there.
I am wondering if it's the NTP-7100 itself or something else down the line.

By the way in the diagram we've got NTP-7000 but for some reason what I've got at front of me is clearly NTP-7100 and besides I did order it already just in case...

[diif]

Re: LG 42LD490-ZB troubleshooting

Ahh a language thing I wasn't questioning the validity of the reflow, I was wondering if one had actually taken place, I have a rework station and I'd only reflow it.
Rethinking this as i doubt it's a reflow issue, I do have a memory of an LG with a screeching sound from the speakers. I can't 100% remember what i did to fix it but i only have one of two NTP-7100 i bought around that time and i might have had to replace the speakers too.

[wyga]

Re: LG 42LD490-ZB troubleshooting

Alright! Thanks a lot. I get my hopes up
I was just thinking then maybe its just some failure on that NTP-7100 without visible issues on the outside of the chip. Which happens sometimes.
Anyway I did order that NTP-7100 so waiting to try it out.