Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

[TheForgottenKing]

Hello everyone, first time posting here so I hope I'm doing everything right.

I just came into possession of a Sharp Aquos LC70LE755U. It was free for me, so with the stand and power cable I only have $30 in this. As such, I'm trying to repair it for cheap.

It works most of the time perfectly, except for an issue with what I think is the power supply. After anywhere from 10-30 minutes of usage, the screen backlight will flicker briefly, and the sound will completely stop working. The sound doesn't start working until I unplug the TV, wait a few seconds, and plug it back in. In addition, at lower brightnesses, the screen backlight flickers randomly.

From my research I've gleaned that both the backlight and speakers are hooked up directly to the power supply board, and now I'm wondering where to start looking as to repairing it. I'm also trying to get a board for cheap and just swap it in.

[dick_barton]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Some photo's of your circuit boards could prove useful.

Have you taken any power supply voltage measurements.

When the backlights and sound go off does the remote control still work.

With a bright light shone at the screen (at an angle) can you see if the picture still there.

Does the led(s) on the front flash?

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Some photo's of your circuit boards could prove useful.

Have you taken any power supply voltage measurements.

When the backlights and sound go off does the remote control still work.

With a bright light shone at the screen (at an angle) can you see if the picture still there.

Does the led(s) on the front flash?

I'll disassemble it tomorrow before work, and try to get some up-close pictures. Is there any areas of interest?

I haven't taken any voltage measurements. I'll try to do so but the intermittent style of the problem might make this difficult.

The remote control continues to work, and the TV continues to properly display an image. The backlight and image stays on, it's just a quick flicker and the image continues to work after.

[alfatv]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Remove power board and check solder joints. I can't guarantee the problem is there, but this is one of the first things to try.

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Remove power board and check solder joints. I can't guarantee the problem is there, but this is one of the first things to try.

Will do this as well. Would it be worth trying to heat the board in an oven to reflow the joints?

[R_J]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

will do this as well. Would it be worth trying to heat the board in an oven to reflow the joints?

NO, DO NOT do this to the power supply board!

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Remove power board and check solder joints. I can't guarantee the problem is there, but this is one of the first things to try.

Will do this as well. W̶o̶u̶l̶d̶ i̶t̶ b̶e̶ w̶o̶r̶t̶h̶ t̶r̶y̶i̶n̶g̶ t̶o̶ h̶e̶a̶t̶ t̶h̶e̶ b̶o̶a̶r̶d̶ i̶n̶ a̶n̶ o̶v̶e̶n̶ t̶o̶ r̶e̶f̶l̶o̶w̶ t̶h̶e̶ j̶o̶i̶n̶t̶s̶?̶

NO, DO NOT do this to the power supply board!

Will not do this. Pretend I never said that. Is there a particular reason this is a bad idea?

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Unfortunately I was wrong about my statement of the speakers being attached to the power board, they are attached to the main board. I've attached an image of the block diagram.

[dick_barton]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

I would take the voltage readings at the power supply connector PD pins 1 to 24 when the set is working and again when you lose the sound.

Have you checked if audio is still available at the headphone output when you lose the speaker sound.

[nomoresonys]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

For re-flowing solder joints on powerboard if needed, just grab a 10-15 dollar soldering iron from a local hardware or a big box store, some even come with some solder included.

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

I've attached images of the power supply, main board, and tcon board respectively. Please do specify if you want a closeup, but I don't see anything immediately obvious.

[Diah]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

you wrote " at lower brightnesses, the screen backlight flickers randomly"

can you upload focused clear photo on the label print chart of the backlight sockets L1 & L2 on the powerboards.

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

LED pinout:


Pinout to the board:


At this point I've bought a cheap replacement power supply just to test if this one is the problem. I'm hoping it's not the main board.

For anyone interested, I'm using this manual.

[Diah]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

At this point I've bought a cheap replacement power supply just to test if this one is the problem. I'm hoping it's not the main board.

LED flickering never being powerboards neither mainboards. or bad soldering too..the LED self are the issue.. one or more of them have spark , which result complete picture flickered and sound cut off too , later on let the reset LED Flickered even at low backlight level. it could be too at one of its sockets behind the screen

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

LED flickering never being powerboards neither mainboards. or bad soldering too..the LED self are the issue.. one or more of them have spark , which result complete picture flickered and sound cut off too , later on let the reset LED Flickered even at low backlight level. it could be too at one of its sockets behind the screen

Where should I look, and what's the process for checking the LEDs? And why would this cut off the sound at the same time?

[Diah]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

Where should I look, and what's the process for checking the LEDs? And why would this cut off the sound at the same time?

cutting the sound could be happened as i think because you were using the tuner as source... if you use HDMI signal or usb media it will not happened.

spark will effect on signal of tuner. if this signal disrupted it will cut sound... look like bad receiving areal signal. if you use external signal such HDMI or other i mentioned before... i dont think the sound will cut off. just the led will keep flickering as you have now... try and test.

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

cutting the sound could be happened as i think because you were using the tuner as source... if you use HDMI signal or usb media it will not happened.

spark will effect on signal of tuner. if this signal disrupted it will cut sound... look like bad receiving areal signal. if you use external signal such HDMI or other i mentioned before... i dont think the sound will cut off. just the led will keep flickering as you have now... try and test.

The sound issue occurred over both HDMI and 3.5mm, I've been using this with a PC and laptop. I've got a new power board and will test that, I suspect it might be an issue with something that powers the 13V rail which seems to power the speakers.

[Diah]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

The sound issue occurred over both HDMI and 3.5mm, I've been using this with a PC and laptop. I've got a new power board and will test that, I suspect it might be an issue with something that powers the 13V rail which seems to power the speakers.

at which resolution..?

[Diah]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

well, i think the best way copy movie on usb flash drive and play it direct on the tv.. to terminated any out source could be the reason.

[TheForgottenKing]

Re: Sharp LC70LE755U - Intermittent backlight flickering and loss of sound.

at which resolution..?

1920x1080, I'll try a usb movie once I reassemble the TV.