Sharp Aquos LC-40UG7252E LCD TV burn in?

[Diah]

Already did factory reset from service menu. Also upgraded firmware, no change.

then take the screen apart to check downside if there any leak of liquid... its just 40 no risk at all.

[jonah1024]

this first time you mentioned the behavior of the screen same at standalone test... then panel issue or its driver at its T-con... try hard reset from service menu

Already did factory reset from service menu. Also upgraded firmware, no change.

[jonah1024]

Not much strange, the ext. psu has more current, tcon components can draw more current due to excessive resistance on oxydized parts, some IC has built in temp. guard and a error shut down happens.. the fault is oxydation as i have said..

With ext PSU, only one of the DC-DC seams to be heating up, the RT6939 (if I remember correctly) and the inductor next to it. It might be that the other IC shuts down as you say?

[Diah]

Why though? 🤔 When the color test happens with the panel receiving only power and no data from mainboard, the defect is still there on all colors. To me this limits the problem to T-con… when T-con also receives data as well I get image, I can navigate menus and so, but everything is smudged as per pictures.

I am trying to understand the process and logic. Maybe I wasn't clear with some specific symptoms.

Here is a new video with the defect. The background should be black and not tinted blue like that.
https://youtu.be/NRPO67Wahj0

this first time you mentioned the behavior of the screen same at standalone test... then panel issue or its driver at its T-con... try hard reset from service menu

[jonah1024]

this tell as i said T-CON and panel are fine... replace MB

Why though? 🤔 When the color test happens with the panel receiving only power and no data from mainboard, the defect is still there on all colors. To me this limits the problem to T-con… when T-con also receives data as well I get image, I can navigate menus and so, but everything is smudged as per pictures.

I am trying to understand the process and logic. Maybe I wasn’t clear with some specific symptoms.

Here is a new video with the defect. The background should be black and not tinted blue like that.
https://youtu.be/NRPO67Wahj0

[Davi.p]

Not much strange, the ext. psu has more current, tcon components can draw more current due to excessive resistance on oxydized parts, some IC has built in temp. guard and a error shut down happens.. the fault is oxydation as i have said..

[nomoresonys]

Any guesses as to why the inductors on driver board are buzzing, do you think it's because something from mainboard isn't getting thru correctly?

[Diah]

I really can’t fathom this:
If I power the Tcon with 12v from TV PSU I get the color test mode (burning mode)

this tell as i said T-CON and panel are fine... replace MB

[jonah1024]

I really can’t fathom this:
If I power the Tcon with 12v from TV PSU I get the color test mode (burning mode)
If I power the Tcon externally, nothing happens on screen (only backlight is on which is wired to TV psu).
I’m using a 12V 3A power brick to power externally since I don’t have a proper lab psu.

I’ve checked the input voltage on board and there seems to be a drop to 11.8V or so. I then used a variable boost converter to get 12.2V on board but nothing happend.

[jonah1024]

Diah
I upgraded the TV using the usb flash method:
(allupgrade_6488_NUX_U.bin and UMC_KMODE.txt) but after the upgrade the issue persisted. The firmware updated from V4.58 to V4.86

what firmware are you referring to?

Iona

[jonah1024]

Hmm this is getting really interesting.

Mainboard is a T.MS6488E.U703
it has a MStar 6488 chip

[Diah]

stop playing with panel t-con... yours issue at MB / Firmware section. show yours MB brand name.

[jonah1024]

Used a separate 12V PSU and tapped into the fuse that normally takes the 12V from the LVDS and the DC-DC ICs and inductors still heatup .
I noticed that the color test mode doesn't start this way, only the backlight is on.

[Davi.p]

what i clearly write, try esternal PSU to ensure internal one is ok, if same heating happens, that is not ok, then the fault is within tcon, second job try cure every oxydized part, don't know exactly how, try dry deoxy spray, for the truth i can't tell you all, also renewing solder joint is a second pass, try every inductor resistance, try freezing on them, locate the problematic one and replace it if needed.. my guess is this set is been outdoor for long and has severe oxydation on almost all the tcon, needs a special treatment, sorry i cant reveal all tricks now..

[jonah1024]

Currently I made it so that the T-con is only receiving the +12V and GND lines from the LVDS (used tape). Is this ok? TV goes into color test loop if powered on.
What should I do now? Try and desolder the corroded inductors?

[Davi.p]

Wait.. don't touch things now... the heating is a new element, also the oxydation i see.is.another element, take an external power supply and supply tcon with its 12v, quite probably power supply is feeding bad the screen, the piece marked with arrow in last pic is an inductor from a sm dc dc converter.. second possible answer, one of the choke inductors is badly oxydized and feeds badly the rest of the tcon (vdd signal, source voltage, maybe are suffering also source cofs and thats why discolorated image)

[jonah1024]

I did the freezing can test with the tv in color test mode with no change in the aspect. I applied froze all the ICs including the main one, the DC-DC ones and the spi,

1) I also did some continuity tests on all capacitors to see if anyone is shorted but not one is. There's only a ceramic part that's bigger than all capacitors but I think that's also an inductor (I marked it with an arrow). I also tested the inductors and all of them have continuity.

2) What I also noticed is that one or two of the inductors is buzzing.
The two inductors circled in red are the ones that seem to be buzzing, not sure if it's one or both since they're pretty close and touching them doesn't help distingusihing. The left beige ceramic one is silent.

3) All the IC's (especially the DC-DC) are really heating up so that ipa evaporates almost instantly, is that normal? I don't have thermal camera unfortunately.

I'll proceed with your next instructions with the RT6939 IC solder in the meantime.

Thanks!

I've attached some closeup pictures of the inductors, the bottom of the RT6939 IC and a video with the whole board closeup.
Closeup Video: https://youtube.com/shorts/DMK1J5xcO0s

[Davi.p]

1) first photo i see spi rom quite distant from Samsung main.chip, appears not to be controlled by him, maybe Samsung is a CPLD and has its own internal memory, but since it is protected i guess it is not there the misfact
2) chips Richtek RT6935 & 6939 are most suspected, both has probably internal registers, has also down side several tiny traces, one of them maybe for Gamma purposes, i would remove solder on those pins and put some other, starting with rt6939..

[jonah1024]

The two DC-DC chips I suppose? cause the main SAMSUNG chip on the Tcon board is protected by some kind of resin.

[Davi.p]

yeah, i supposed this is a difficult case, not sure of any thing, but what about the others IC?
correct myself: sure about this is a tcon/panel issue.. 80% sure this isa bad soldering issue.. continue diving into trouble and you'll get success.. turn on tv, wait fault to happen, take freezing can with little hose, spray very few on components one at a time starting with bga or qfn IC