DSE GE6877 problem with LEDs???

[maxvalutech]

This is one of the cheap sets given to me "sound OK but no picture". I immediately suspected tcon and sure enough this has bottom mounted bonded screen driver combined tcon. But in testing set something strange in that standby (which seems normal) the main caps read 368v and steady. At switch on their voltage starts fluctuating quickly anywhere between 180 - 330v however the 5v and 12v points are good and the leads to LEDs steady at first one 79v and 25v next one 79v and 0v. At no time does screen flicker or show signs of life. I'm not well up on the LED circuitry but the readings don't look right although they are steady whilst main caps fluctuating madly. What are your thoughts.

[budm]

Re: DSE GE6877 problem with LEDs???

Hmm, the power supply has no PFC Voltage booster (I do not see PFC Inductor) so I cannot see how the Voltage measured right between the two legs of the main filter caps can be as high as 368VDC unless your incoming AC; at 240VAC the Voltage on the cap should be around 240VAC x 1.414 =339VDC, so may be your incoming AC is much higher than 240V? 368VAC x 0.707 = 260VAC incoming.
Can we see good clear straight shot pictures of the whole top and the bottom side of the power supply board?

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

Thanks budm and the high voltage we have seen before. I know we sometimes get around 250ac but anyway I used another meter now and this time in standby the main caps fluctuating up to 346v then down then up again so seems to be turning on/off in standby. Set turned on main caps are now reading zero!! But LEDs own power circuit with stable 79v but no lights.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

Pics

[Andrew F. Ali]

Re: DSE GE6877 problem with LEDs???

Appears to be a bad string of LEDs. Do you have a LED Backlight Tester?

[budm]

Re: DSE GE6877 problem with LEDs???

Thanks budm and the high voltage we have seen before. I know we sometimes get around 250ac but anyway I used another meter now and this time in standby the main caps fluctuating up to 346v then down then up again so seems to be turning on/off in standby. Set turned on main caps are now reading zero!! But LEDs own power circuit with stable 79v but no lights.

It think you have measurement error, impossible to have 0V on the main cap and still have 79V on LED power supply. The power supply only has ONE power Transformer to supply all the Voltages so 0V to drive the Transformer primary winding driver circuits = 0V output.

[budm]

Re: DSE GE6877 problem with LEDs???

What is the Voltage ratings for those 3 yellow caps by LED connectors?
So far it looks like you have open circuit in one of the LED string, the one that read 0V on the LED connector.
You can swap the two LED connectors to see if the 0V reading will follow or not.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

No backlight tester Andrew and yes I'm thinking a led strip gone oc. But have been caught recently with two sets I was sure had led problem when they didn't - wasted effort to dismantle only to find all good! Also the circuitry in the ones I've looked at have all been different - with the voltage constantly available to leds at set turn on as in this case why don't LEDs display? I can only think the circuit is left open waiting on the main to activate closure of the circuit (to earth) via PSU.
Anyway whilst awake and fresh this morning and for budm this is what I measured.....
Set in standby, all connected, red led on.
Main caps fluctuating wildly 0-340v, led connectors 60 & 17v. 60 & 0v all steady
Set turned on, all connected, blue led on.
Main caps slower fluctuation 0-33v, led connectors 78 & 34v. 78 & 1v all steady
Main board disconnected, set powered up, no standby led.
Main caps steady at 348v, led connectors 55 & 15v. 55 & 0v steady.
When led connector leads were swapped the voltages stayed with their lead.
The lone black cap near led connectors reads the same top voltage as on the connectors. Cant see its details as that side stuck down. The yellow caps are rated 80v 82uf so would seem to be part of that circuit although voltage rating is low in that case.

[Andrew F. Ali]

Re: DSE GE6877 problem with LEDs???

So with the Main Bd. disconnected from the PSU the backlights came On and stayed ON and all other supply voltages were good. If that is so then I would think the PSU is OK and the Main or T-CON Bds have a problem. If the T-CON Bd. is separate from the X-TAB Source Bd/s you could probably try disconnecting the T-CON Bd. to see if the set will power up.

[budm]

Re: DSE GE6877 problem with LEDs???

No backlight tester Andrew and yes I'm thinking a led strip gone oc. But have been caught recently with two sets I was sure had led problem when they didn't - wasted effort to dismantle only to find all good! Also the circuitry in the ones I've looked at have all been different - with the voltage constantly available to leds at set turn on as in this case why don't LEDs display? I can only think the circuit is left open waiting on the main to activate closure of the circuit (to earth) via PSU.
Anyway whilst awake and fresh this morning and for budm this is what I measured.....
Set in standby, all connected, red led on.
Main caps fluctuating wildly 0-340v, led connectors 60 & 17v. 60 & 0v all steady
Set turned on, all connected, blue led on.
Main caps slower fluctuation 0-33v, led connectors 78 & 34v. 78 & 1v all steady
Main board disconnected, set powered up, no standby led.
Main caps steady at 348v, led connectors 55 & 15v. 55 & 0v steady.
When led connector leads were swapped the voltages stayed with their lead.
The lone black cap near led connectors reads the same top voltage as on the connectors. Cant see its details as that side stuck down. The yellow caps are rated 80v 82uf so would seem to be part of that circuit although voltage rating is low in that case.

That is not making any sense to me to have Voltage fluctuation of 0 ~ 340V on the main cap.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

The backlights never came on Andrew and the readings make no sense to me either budm other than the main caps seem to charge/discharge and only when mainboard is connected but the fluctuations are so fast and all over the place so it is difficult to see any pattern to it. At the same time led voltages are steady so cap/s there are holding charge!!! I will pull it apart and check LEDs as I think if 2 strings are there then the readings should be the same and they aren't.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

I finally pulled this screen off the set and got down to LEDs but the white reflective paper is well glued down in places and is brittle so it just started tearing when I gently tried its removal. However from what I could see there is no sign whatsoever of any LED or strip having a problem. This set is not worth much time or effort let alone funds. Am putting it back together and along the way will test with feed to screen tcon long board removed as suggested above (missed that earlier I'm sorry). Other than that then main must be the problem if those LEDs are as OK as they look.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

By the way did you notice 11 LEDs x 4 strips and 2 feeds. Couldn't see the actual wiring but strips horizontal so each row 1 x 6 and 1 x 5 ???

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

No difference with tcon lower board disconnected and same results with voltages being LED leads steady readings and main caps all over the place and yes even 0 voltage reading seen (maybe dmm getting flummoxed!) until main boad lead disconnected then PSU normal. Off to the tip it goes sans PSU.

[budm]

Re: DSE GE6877 problem with LEDs???

May be you need to try another meter since no way the main cap can discharge that fast to go to 0V and charged back up fast, there will be lots of inrush current when cap is charging up from 0V, and other circuits that get the Voltage from that main filter cap cannot be steady when the main supply Voltage swings wildly like that.

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

I have used 2 meters on this one budm the first (post 1) does seem to over read by about 7% when I've compared the two on different sets. There is something very strange in circuitry as LED voltage does remain stable/steady while main fluctuates very quickly but I didn't then check the minor voltages at all since first time. The PSU is OK I believe as it acts normally as soon as main is disconnected. Can never find out any info on these generic sets with store brand and that seller went bust a couple of years ago. Its in dump now.

[Amraks]

Re: DSE GE6877 problem with LEDs???

Did you do a recap?

[maxvalutech]

Re: DSE GE6877 problem with LEDs???

No to recap as the PSU worked as it should when isolated from main. No circuit info for main and those boards put me off as soon as I see one.