Dick Smith GE6824 no backlights plus more

[dkneyle]

One of these cheap Chinese TVs made for the re-badging market. 32 inch. Pulled from the dumpster at the garbage tip. Surprisingly clean, only just dumped I'd say.
The indicator LED changes from Red to Green. No sign of any image even with the flashlight test. All voltages other than backlight come up good. The BL-ON signal is good and remains constant. At power on the backlight give a quick flash, but a check of backlight voltages show a peak at the expected voltage then a quick cascade back towards 0 volts.
So the mainboard appears to be sending out the correct signals to start the TV. For some reason we get the volts for the LEDS but then this collapses. And no sign of a video signal to the panel.
What am I missing here in this diagnosis?

[dick_barton]

Re: Dick Smith GE6824 no backlights plus more

Looks like a classic led fault.

[dkneyle]

Re: Dick Smith GE6824 no backlights plus more

I'd thought because I saw the leds flash on then they were OK. You think not?

[dick_barton]

Re: Dick Smith GE6824 no backlights plus more

No. The flashing leds tend to be symptomatic of led problems. Looks as though you may have some shorted out leds. It could also be poor interconnections between the strips but I think it's a led problem.

[dskall]

Re: Dick Smith GE6824 no backlights plus more

Have you looked with menu up? With bad led's voltage will ramp up till it hits preset voltage and go into protection. If all is good it will not reach cutoff voltage. I have an led tester as backlights are the new plague now. I can light up screen etc, with it.

[dkneyle]

Re: Dick Smith GE6824 no backlights plus more

Even when the LED string is unplugged from the power supply it comes up to voltage then quickly cascades to zero as the capacitors discharge. Is that because it detects an open circuit and shuts off the LED supply?

[budm]

Re: Dick Smith GE6824 no backlights plus more

The LED driver circuit has two protection modes: over Voltage output protection when load is not connected, then over current protection if the load draw to much current.

[budm]

Re: Dick Smith GE6824 no backlights plus more

Can we see the good straight shot of the back side of the board? Also pictures of the whole back side of the TV showing how all the wires are connected.

[dkneyle]

Re: Dick Smith GE6824 no backlights plus more

Stripped the panel down. Found one LED that appears open circuit. I can make all other LEDs fire up when I put about 2.5 volts across them. Interestingly, the diode test function give 0.75V forward conduction for nearly all. A couple are at about 0.85V, and one doesn't read anything although lights up when volts are applied. Would I be right in assuming these different voltage LEDs might be on the way out?

[dkneyle]

Re: Dick Smith GE6824 no backlights plus more

I sweated off the dud LED and replaced with one from another strip for a larger TV panel. Not sure if it's compatible? On the diode reading of my meter I couldn't get a forward bias reading. Anyway, re-assembled, and at switch on I had backlights and a menu. Confirmed therefore I had a panel backlight fault originally I guess? The backlight had a slight flickering to it like a joint about to go open circuit. I wondered about my workmanship on the LED replacement job? Lasted about 2 minutes before it failed. Dropped back into "2 seconds to black" syndrome. Then eventually nothing brought the backlights on.
It's an Innolux panel. I'm seriously thinking of junking it. I reckon other LEDs will fail soon enough.

[dskall]

Re: Dick Smith GE6824 no backlights plus more

Well seems a shame to junk one for backlights. Individual leds are inexpensive. Depends on your reason for repairing. I do it for hobby so would replace them all individually if necessary. Plenty of people have good success with various repair methods. Some say like you the repair doesn't last. I sell mine after and haven't had one come back yet. Need to keep backlights turned down as manufactures drive them to hard so they fail and you buy new tv

[dick_barton]

Re: Dick Smith GE6824 no backlights plus more

I sweated off the dud LED and replaced with one from another strip for a larger TV panel. Not sure if it's compatible? On the diode reading of my meter I couldn't get a forward bias reading. Anyway, re-assembled, and at switch on I had backlights and a menu. Confirmed therefore I had a panel backlight fault originally I guess? The backlight had a slight flickering to it like a joint about to go open circuit. I wondered about my workmanship on the LED replacement job? Lasted about 2 minutes before it failed. Dropped back into "2 seconds to black" syndrome. Then eventually nothing brought the backlights on.
It's an Innolux panel. I'm seriously thinking of junking it. I reckon other LEDs will fail soon enough.

Buy one led strip for this model (ebay/shopjimmy) and then use leds from this strip as replacements knowing that they are the correct leds.
Turn down the backlights and hopefully you should get many months of further use.