Sharp LC70LE747 Flickering - darkening gradually to the right side

[SmartSarah]

Dear,

I can not pinpoint the following problem on my Sharp TV LC70LE747E.
While the left side of the screen is not affected at all the right side of the screen gradually fades to a kind of dark. I can best describe this darkness like a totally worn out CRT display or a gamma correction totally out of range. This darkness flickers like a flame, a dark one tough.
Sometimes when I restart the TV it disappears for a while.
The problem worsened over time the last few months.

I've replaced the t-con module without success. The problem remains.
I've checked as good as possible for bad contacts cables and ribbons by moving them and applying contact spray. No difference.
I've checked on poor joints or some mechanical failures on PCB's by ticking on them with the grip of a screwdriver. No difference. Wiggling the panel doesn't make any difference either.
I've heated all pcb's with a hairdryer, no impact. I've cooled the pcb's with freeze spray, no impact.
I've checked the 2 output voltages PNL 12V and UR 13.2V on the power supply to the main board and the t-con board. They are steady and spot on.
I've done a factory reset. No effect.

Since the problem worsened over time it could relate to a degrading capacitor, but that's just a wild guess. I just hope it's not the panel itself since that's not worth repairing / replacing.
Can anyone here give me a clue what I should try next?

Kind regards,
Sarah

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

from first thought via yours description the LED backlight issue. but will be better if you upload photo of the issue

[dskall]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

The video on bad side is good or bad or just getting dark?

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

The video goes bad as well, vertically misplaced.
Sometimes when I power the TV off for 10 minutes and back on, the fault disappears and it won't return during that session. A short power cycle never does the trick.
The video in attach doesn't show the vertical erratic behaviour but it happens. For this reason I think I may exclude a backlight issue.

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

bring the BL setting 35% or less see if the issue remain after you power off and on straight

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

BL goes from -16 tot +16 on this set. I brought it down to -8, no effect. Even after power cycle. Did the same BL to -16 and power cycle. No result.
I noticed something weird tough. After powering off there remains an still ghost image on the troublesome side for 5 seconds.

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

you need to put the original T-CON back
read page 33 at service manual

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

i can see the effect with darkness are not sup line or block on screen... but it had effect to uncertain wide image.. this couldn't be panel as its block, but BL could be... please measure all voltage on BL socket at PCB between LED+ & LED-

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Need to wait before it goes bad again. There is no problem right now.
The voltages on the 3 led strings are identical now. Depending on BL level between 130 and 191 Volt. Assumingly normal.

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Need to wait before it goes bad again. There is no problem right now.
The voltages on the 3 led strings are identical now. Depending on BL level between 130 and 191 Volt. Assumingly normal.

maybe because u reduse the bl setting !!!

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Therefore I've set BL to where it was initially.
Anyway to be continued.

[dskall]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Ok, looks like center from video. Can you look from back and see if backlights flickering?
If not t-con, then likely panel.

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Small update
In order to measure the BL voltages I hooked up a small multi-meter with it's tilt-stand hanging on the power board.
Since then the TV worked normally.
So bad joint close to the upper part of this board? Earlier measurements with the same multi-meter setup gave me a similar impression but after a while the error returned, so I left the theory.
Now, after measuring the BL tensions, hanging the multi-meter on the board and applying some mechanical pressure on the backlight connector in order to make good contact, the error remained away.

So I took the power board and re-soldered all pcb joints in the power lanes starting from the LED+ connector down to the two diodes on the secondary side. This includes a power diode, a transistor, a coil, some resistors and bridges. This for the 3 LED backlight circuits. From experience I'm aware that "hot" power components might de-solder themselves. Some of the joints looked suspicious but I honestly can't tell if they really where troublesome. Since we started using low lead solder, good joints don't shine anymore!
So far, problem gone!!!

Anyway, I'll observe situation for a few weeks before I feel confident I've definitively hit it.
If the problem stays away, I'll call it off. Meantime, many thanks to Diah who gave me adequate directions.

Cheers

Sarah

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Perfect work Sarah. thanks for following up.
yes you are right about the low lead solder.. this why if i want to check joint point solder always do it under magnifier to be sure they are fine.

[nomoresonys]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

that symptom worsen over time, can be a good indicator of bad joint/s for sure also bad cap/s as you mentioned, well done.

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

Bad news. The problem returned.
Backlight
- BL voltage on the 3 strings are identical, 190VDC and stable
- Looking from the back the backlight illumination is steady
I can't get my head around the following: when the TV starts without symptoms it will probably stay without problems (24h or more if you like), when it starts troublesome it won't recover, whatever I do. It's like something interferes with the boot sequence.

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

can we see the PCB from top and downside. as well the socket of BL. ?
190V i found it so much... what did the print chart on PCB say?

[Diah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

BTW. please Inter adjustment mode.. .. so we can see if there are any error registered at page 1

Entering and exiting the adjustment process mode
1) Unplug the AC power cord of running TV set to force off the power.
2) While holding down the “VOL (-)” and “INPUT” keys on the set at once, plug in the AC power cord to turn on the power.
The letter "K" appears on the screen. This state is in Inspection mode.
3) Next, hold down the "VOL (-)" and "CH (down )" keys on the set at once.
Multiple lines of blue characters appearing on the screen indicate that the set is now in the adjustment Process mode.
If you fail to enter the adjustment process mode (the display is the same as normal startup), retry the procedure.
4) To exit the adjustment process mode after the adjustment is done, unplug the AC power cord to force off the power.
(When the power is turned off with the remote controller, once unplug the AC power cord and plug it in again.
In this case, wait for 20 seconds or so after unplugging.)

[dskall]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

I don't think this is a mainboard problem. You eliminated T-con. I would focus on side COF's. May have a bonding issue.

[SmartSarah]

Re: Sharp LC70LE747 Flickering - darkening gradually to the right side

The included video is during a reasonable start-up.
(Don't be mislead by the colours my camera made out of it.. The start-up logo is red on black and not white on blue as the video apparently looks like.)
The photo is one of the worst frames taken out of this video.

With reasonable start-up I mean the right side doesn't fade to much, does flickers and jumps only briefly. This is a good start and during the adjacent session it won't give a kick.
If it keeps jumping during the presentation of the start-up logo, than it's bad and will not recover during the next session. I'll need to leave it off for a long time and hope next start-up is better.

BTW
The BL voltage depends very much on the image setting. 130V is a low setting I tried yesterday, 190V corresponds with the dynamic setting I usually select and it is indeed really bright.