"Dick Smith" 55" LED backlight issue - model GE6880

[nomoresonys]

Thanks for the followup Dagav.

[dagav]

For others encontering this fault, the solution for this TV-set was reprograming the eeprom on the mainboard.

[dagav]

+5V stby ok

[dkneyle]

Have gone trough the thread, and tried to find some tip, for the JVC - LT-50E73, without luck. Despite the rather old thread on TV5001-zc02, I hope some can give some clue about a JVC - LT-50E73 TV stuck in stby,(no reaction either on remote or buttons on TV), and with no backlight, with this powerboard inside. Voltage missing on the main connector is on/bk. On Led connectors voltages are 0, on all outputs, and no difference if they are connected or not. My ledstrip tester says 300V, open circuit, on both strips, so they are faulty. But can it also be a faulty motherboard since the TV is stuck in standby?

Dagav, if your LED tester says the panel LEDs are busted, then what is the point of going further? Those testers are pretty good at firing the LED string if there's nothing wrong with them. From what you have described, I'd certainly also suspect a failed mainboard if you aren't getting any turn backlight on voltage signal. I assume you have +5v standby supply?

[dagav]

Have gone trough the thread, and tried to find some tip, for the JVC - LT-50E73, without luck. Despite the rather old thread on TV5001-zc02, I hope some can give some clue about a JVC - LT-50E73 TV stuck in stby,(no reaction either on remote or buttons on TV), and with no backlight, with this powerboard inside. Voltage missing on the main connector is on/bk. On Led connectors voltages are 0, on all outputs, and no difference if they are connected or not. My ledstrip tester says 300V, open circuit, on both strips, so they are faulty. But can it also be a faulty motherboard since the TV is stuck in standby?

[nomoresonys]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Good point dkneyle, nothing worse than a tv that can't even produce decent color, not worth messing with.

[dkneyle]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Yes, in my case it turned out to be a failed LED rather than power supply issue.

Anyone following my post in this thread, here are my thoughts. These VERY CHEAP DSE/Kogan TVs use really cheap and nasty low grade panels. I shorted out the dud LED to get the panel operational again. When I did so we had a vertical line. Obviously the panel surgery had caused a panel contact to slightly come away (even though we'd been as careful as we could in performing the operation). A slight tweak of the panel and it comes good, another tweak in the opposite direction and it's back again. No strength in the frame whatsoever.
The colour rendition is woeful. Reds are more a magenta. Greens are a lime-green. (I've had this with other Kogan TVs and I've actually sent them back for a refund because they look so bad.)
My advice? Scrap the TV. That's what I did today with the second one. No point wasting time trying to get it operational. Advertised the boards for sale as second hand parts.
By the way, identical model numbers, but different T-Con and LED strips. Probably entirely different panels.

[dkneyle]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

TL431 can maintain a constant current of 100mA and TL432 of 50mA

Thanks Dick for your input.
Which then doesn't really explain how FamilyMan's workaround got his SMPS operational, since it isn't really anything to do with voltage thresholds?
And from a manufacturing viewpoint, why specify TL431 on one part of the circuit and TL432 on another, since they are basically the same device? And then why substitute TL432 with another part rather than TL431, since they are obviously available to the manufacturer as they have been used elsewhere on the board. All very weird.
I've ordered one of these new clever constant current output LED testers. I'm pretty sure I'm going to find I have failed LEDs rather than any problem with the PSU. These cheap re-badged Chinese TVs use inferior panels and I know from past experience the LEDS do not last. But as I've got two TVs I can salvage some LED strings and swap and get at least one going. I'll update this post to assist other Aussie's who are trying to repair these Dick Smith TVs.

[dick_barton]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

TL431 can maintain a constant current of 100mA and TL432 of 50mA

[dkneyle]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

I've currently got two of these in with identical fault. I've followed this thread for advice.
I changed the snubber diode (which did not measure any resistance fail) as others reported. Changed out with a 600V fast recovery snubber I had on hand without any luck.
Then I started to look at Family Man's post about the TL432 device. Now what I can't understand is why use a TL431 and TL432 in different parts of the circuit. My reading of the datasheets and elsewhere suggests they are interchangeable, adjustable down to about 2.5V. So why specify two different types on the schematic and why then substitute a different part?
I've got a heap of new TL431s on hand, so I might experiment and see what happens.
Of course, it might too be that I have failed LEDs in both TVs (highly likely) and I'm going up a dry gulch with all of this?
(I think I'll invest in a backlight tester - especially given how often I want to know if I have faulty backlights - probably beats having to pull the panel apart.)

[nomoresonys]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Some images there, might help, that's if your model number is same as the OP: https://www.google.com/search?q=GE68...w=1280&bih=645

[chrise]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

I am trying to figure out what is wrong with my power board and I noticed Q111 is completely missing from the board. There appears to be solder from where one may have been attached. Does anyone know if this is present on the boards you have worked on? Hoping that possibly someone has some pictures or an old board laying around they could peek at.

[chrise]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Thanks budm, you're a life saver

[budm]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Hi, I know this is an old post but I am having the same issue. I cannot find the schematic for the board mentioned and the link in the first post no longer works. Does anyone have a schematic they could share with me?

Luckily I download and save the file.

[chrise]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Hi, I know this is an old post but I am having the same issue. I cannot find the schematic for the board mentioned and the link in the first post no longer works. Does anyone have a schematic they could share with me?

[nomoresonys]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Nice work FamilyMan.

[FamilyMan]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Well, for what its worth, this is my experience.
I collected one of these off the kerbside cleanup, no backlight. Went through and tested each backlight LED in turn and found two bad ones. Since it is fed essentially by a current source, I just shorted out those two with a piece of wire and put it all back together and it worked for 12 months. I put up with the fact that there are two widely separated slightly dim areas of backlight. I'm the only one who can see it. It worked that way happily for 12 months or so.
Then the backlight went out again and I immediately suspected another bad LED, so stripped it down and it all checked out ok. I even went to the trouble of creating a new test 140V power supply, and all the LEDs came up just fine.
Anyway, to cut a long story short, went through all of the issues in this forum to no avail. In my case it turned out to be U204, on the schematic as a TL432 2.5V shunt regulator. But mine had fitted a MB432A https://pdf1.alldatasheet.co.kr/data...TC/B432AM.html, which you might assume is a TL432 equivalent. But no, it is a 1.25V part, not a 2.5V. I twigged to this because the reference pin was sitting at 1.3V and the part was conducting, so I assumed it was stuffed, but it all checked out ok. Anyway, this causes no end of havoc with the feedback because the voltages are out by a factor of 2. The wonder is that it worked at all, but I suspect the main feedback is via the OB3354 mechanism which isn't so voltage reference sensitive. However, in the initial case I think the backlight voltage was low by a factor of two and so I think it was more prone to triggering the fault and killing the backlight.
So, without a proper TL432, I retained the MB432A and fitted 100k to R237 (vacant), put 2k2 in parallel with R235. and replaced R232 with 47k to make the feedback values correct for a 1.25V reference. I have no idea if that was all necessary, but that is what I did. And with all of the boards back to make the power on and adjust signals correct, up it came.
YMMV.

[joezzz]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Hi guys, I have the same scenario .... I went ahead and changed over the FR307 to no avail. Back light goes out after about 20 minutes ,,, then turned on again it goes off after approx 12 minutes,,,,then again after 1 minute .....then just flashes all the time voice works ok ..



i have used a fan for cooling and have since soldered all the connections on the board to no avail . I bought this set on the 29th of july 2016 now this...any advice guys..

PS strangely it was turned on by my niece and worked for hours until I turned it off..


any ideas guys

[streetford@hotmail.com]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

Hey Rockit711,
I am fixing the same tv for a friend. I also need to replace D112 as mine has the FR307 part in it. Did the FR607 do the job ok or did you go with a different one?? Thanks... if not for your determination no one would be fixing these

[rockit711]

Re: "Dick Smith" 55" LED backlight issue - model GE6880

check D112 (large diode on the primary side of the LED transformer circuit) it was a "FR307" on mine. it resulted in the same "flash" then nothing as you describe. May need to be de-soldered to get a good test on it. Also do a resistance check on it in case it has partially failed (as mine had).


If that isn't it then I'd recommend looking at pin 9 of the OB3354 chip (its the 16 pin SMD one just to the left of the LED connectors you have marked in your picture).

Pin 9 is the fault pin, it will trigger if the driver detects a failed LED (short or open) and shut down the backlight.

if pin 9 has triggered (high output from memory) then it means the fault is almost definitely a failed LED(s) in the backlight and you will have to isolate the failed LED and replace.