Sharp LC-52LE830U no backlight

[73buick]

Getting the one long one short blink. If I do the force start, I get picture, but no backlight.

With above and LED connector plugged in, meter on LED1-4+ starts at 40VDC (maybe higher, but that is after 5-10 seconds after the force start) and then slowly drops stays around .1VDC. LED1-4- show 0VDC.

With unit off, ohm reading on LED1-4+ are about 2.7MOhms, LED1-4- around 1.9MOhms.

LED connector unplugged, ohm readings off PSU board pins the same. Power reading, this time on LED1+ I caught it starting at about 120VDC, but again slowly was dropping.

Bad PSU board? I should be getting steady high VDC (150-200 I assume) out of the LED+ pins from it with the LED connector off, right?

[R_J]

Re: Sharp LC-52LE830U no backlight

The actual voltage depends on how many led's and there configuration. The led supply also detects if there is a problem and shuts down if it detects a fault.
You need to have your probes on the +led then turn on the tv as the voltage will come up then drop if an error is detected.
You can not check the led strings with a ohm meter. I would suspect you have one or more bad led's in the panel.

[budm]

Re: Sharp LC-52LE830U no backlight

How about the Voltage readings on the LED- (Cathode return) for each LED -? You will have to leave the probe on the pins while turning the TV ON.
Pictures of the boards an what we are dealing with?

[73buick]

Re: Sharp LC-52LE830U no backlight

Here is the board in question. Just did this test. Plugged in, lamp error flash. Meter on LED1+, 0VDC. Leaving probe on LED1+, did a force start. Meter stayed at 0VDC. Tried on LED2+ as well, same thing.

[budm]

Re: Sharp LC-52LE830U no backlight

"With above and LED connector plugged in, meter on LED1-4+ starts at 40VDC (maybe higher, but that is after 5-10 seconds after the force start) and then slowly drops stays around .1VDC." So you were getting 40V on the LED+ and now you are getting Zero?

[73buick]

Re: Sharp LC-52LE830U no backlight

The first time I wasn't measuring right away. Not sure if that would make a difference. I am going to test again both ways to be sure.

[budm]

Re: Sharp LC-52LE830U no backlight

You need to leave the probes in place before tuning on the TV, then you will watch the meter to see how high the Voltage jumps up to when the TV is turned on and how low it goes down to after 10 seconds.

[73buick]

Re: Sharp LC-52LE830U no backlight

Okay, did it again. These readings are going from lamp error state to forced start up state. Probes are set on pins from the get go.

LED1+: Takes 3-5 sec from the relay click to jump to 140VDC for a second, then starts dropping. After about 10 sec, its around 20-40 VDC and still dropping.
LED2+: Same
LED4+ Same

LED1-: Again about 3-5 sec from the relacy click and jumps to about 70VDC for a second and starts dropping right after.
LED4-: Same

With LED connector off, +/- pins stay at 0VDC.

[73buick]

Re: Sharp LC-52LE830U no backlight

Bump. Bad LED?

[budm]

Re: Sharp LC-52LE830U no backlight

Okay, did it again. These readings are going from lamp error state to forced start up state. Probes are set on pins from the get go.

LED1+: Takes 3-5 sec from the relay click to jump to 140VDC for a second, then starts dropping. After about 10 sec, its around 20-40 VDC and still dropping.
LED2+: Same
LED4+ Same

LED1-: Again about 3-5 sec from the relacy click and jumps to about 70VDC for a second and starts dropping right after.
LED4-: Same

With LED connector off, +/- pins stay at 0VDC.

You have four LED strings so what happen to LED2-, LED 3+, LED3-?

[73buick]

Re: Sharp LC-52LE830U no backlight

Sorry, same readings for the others, too.

[budm]

Re: Sharp LC-52LE830U no backlight

1) So to be clear, all four LED (-) Cathode return of the LED strings pins shows 70V after the relay clicks and then drops down right after. Correct? 70V reading on the Cathode return lines are high, typical value is around 20 ~30V range.
Need to do more investigation.

[73buick]

Re: Sharp LC-52LE830U no backlight

Okay, so I went and tested everything again. I had my intern doing it before and wanted to just do it myself. I did each test twice to confirm readings. So starting with TV unplugged and LED connector plugged in.

Plug in TV, lamp error flash and 0VDC on LED1-4 +/-.

Force power on: Relay clicks. LED1-4 +/- will jump about a tenth of volt for a second. After about 25-30 seconds, LED1-4 + jumps to 140VDC for a second, then relay clicks again, voltage drops by half and continues to drop and lamp error flash returns. LED1-4 - jumps to 70VDC for a second, and does the same thing.

One thing to note, when I first was testing this last week initially, before I had the back off, I could force power it on and it would stay on. It wouldn't click back to lamp error after 30 seconds.

[73buick]

Re: Sharp LC-52LE830U no backlight

Bump. I have an LED tester on the way, too, just in case.

[73buick]

Re: Sharp LC-52LE830U no backlight

Okay, so I believe I confirmed bad LEDs. Using the LED tester, I unplugged the LED connector and tested LED1+/- through LED4+/-. LED1,3,4 are tested at around 70-72VDC and I could see areas of light brightening up on the screen. LED 2 at first went to around 85VDC, then after a few tests the tester just would drop from the default 327VDC to maybe 323VDC, a couple times would flucuate from 130 to 260 and back and forth, so I am assuming that LED string is bad.

[budm]

Re: Sharp LC-52LE830U no backlight

Yep.

[73buick]

Re: Sharp LC-52LE830U no backlight

Okay, so I got the new LED strip in. Plug in, still on lamp error. Do force start and it turns on and lights up good. I can go into menu settings, etc, looks good. Unplug and plug in again, still on lamp error blinking. Force start, go into menu and do a reset. No change. Look up and see it probably needs to go into service mode to reset the lamp error code. Instructions I find online and in the service manual say to push Vol- and Input buttons on TV, then hit power and keep the first two pressed until I see the K icon show up. I have tried over a dozen times now, the K never shows up. The turns on, but no K icon. I tried once doing with TV unplugged first, but that just made it go back into error lamp mode. One thing I did notice is sometimes the touch buttons haven't been responding, but I don't know if that is just a normal thing if maybe the get touched too many times and it locks itself out for short time b/c when it does that, if I just wait 10-20 sec, then they work. I thought maybe I need to use the remote (I don't have it presently), but the service manual says to use the buttons on the tv.

[vinceroger69]

Re: Sharp LC-52LE830U no backlight

have you retested the 4 led strips with your led tester what readings are you getting now

[73buick]

Re: Sharp LC-52LE830U no backlight

All test same now, 70-72V using the LED powersupply/tester.

[budwich]

Re: Sharp LC-52LE830U no backlight

I think your issue is indeed, you have to get into the service menu to reset the counters. Your "words" on the process for getting there give me the impression that you are "hitting" the power button.... that's not what you have to do, you have plug into power while holding down the buttons that you indicated. That should get you there. Without resetting the error counters, your set will always be in "error" as a factory reset doesn't do anything for the counters.