Westinghouse LD-4680 - no power - seems to be stuck in stanby

[Dgtech]

I read another post here about these sets. The post said to disconnect the ribbon cables and power up and reconnect one at a time. I tried this method first. There is no response. I got 19 volts on the board in a few spots.

Only one 1117 regulator is being powered at this point.
Q25 has 5 volts in and 3.3 out.

Is there any way to trick this on?

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

The voltage is only present on Q25 when ribbon cable con 10 is disconnected. That's the one on to the right.

[tibimakai]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

On mine, I had the same exact problem, as with the 4665 model. Bad ribbon cable at the LED strip.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Which ribbon? See pic.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

I tried the method of removing both ribbon cables and got no LED status at all. Is there a way to jumper something to tell the main board to go into power up mode?

[selldoor]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Picture of the power supply? any clues on the connectors from it to the logic/main board as to what the pins are?

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Is there a service manual somewhere for this set? I will play around with the ribbon cables a little more when I get the chance. I just wanted to check some test point voltages or something. I hope it's just the ribbons. I just didn't take it all the way apart yet. Is it hard to get down to the LED strips?

[ecking767]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Which ribbon? See pic.

the ribbon in the picture are not the LED ribbon cable

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

The ribbon cables in question are the two on the 2nd picture in my first post right?

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Ok...update.

I disconnected both ribbon cables and reconnected power. Checked screen with flashlight and there was a menu. I don't know about my confusion from before.
So... to make a long story short, the ribbon cable that goes into connector con 10 is grounded on all pins.
For anyone following this post in the future, one of the meter leads touches the aluminum chassis and one touching the pins of the ribbon cable with the meter set to ohms. Zero ohms is a short. Bad

Now I must fix the short just as those on the other threads did for similar sets.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

I have never gone this far with a tv. Where is the other side of the ribbon cable? I don't see the led light bar or strip.

[selldoor]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

May be a bit late for this but I think this is a way of testing Led backlight
to save taking it apart if its ok.

http://www.technibble.com/forums/showthread.php?t=38262

[budm]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

http://www.shopjimmy.com/westinghous...or-ld-4680.htm
Looking at the picture of CON10, that is the Return side of the LED (Cathode) which will be connected to very low Ohms current sensing resistors to ground to maintain constant current.
If the LED assembly is shorted to the chassis, you should be able to take the resistance reading on the Anode side which is connected to CON11. So pull both white ribbon cables off the CON10, 11 and then probe each exposed conductor on the ribbon cable against chassis to see if any one one of them had shorted to the chassis.
BTW, what DC voltage do you get on the two legs of those two green caps sitting between the CON11, 10?
P/N of U25, 26?

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

I have to go back down and check those voltages Bud.

Here is something interesting - Refer to the pictures below.
I took these pictures to show that the ribbon cable has some sort of ground. Here's the thing though, with the set standing like this, If I slightly push the screen forward (not much), the resistance will increase/decrease. I have done this directly from the ribbon cable - disconnected from the board. I just wanted to show in the picture a good test point to test this theory.

I will try to light this thing with that site that Selldoor suggested. Although, I would have thought that if the one side was grounded, in any case, with just the anode tied high from the board's supply voltage, the lights should have come on being as it would have had a complete circuit.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Quoting from another post found here:

https://www.badcaps.net/forum/showth...t=22932&page=4

I have just picked up one of these for $40 and I have fixed it already.
Thank you for pointing out where the problem is.
I think that I may have found the real problem. The two ribbon cables at the LED strips wrap around the LED's aluminum strip and the ribbons short out right there.
I have applied some tape under the ribbon cables and the TV runs perfectly.
Remove only the bottom black plastic from under the panel, no need to take the whole screen apart. The metal clamps have to be removed also, because the panel has to be lifted a bit to remove that black plastic piece.
Nice easy fix, using a bit of tape

I'm going in... Thanks for the help all.

[budm]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

"I took these pictures to show that the ribbon cable has some sort of ground" Those two white flat ribbon cables that go to the LCD panel LED strings should show no resistance reading between the conductor on the end of the cable and the chassis (cables not plugged into the sockets CON10, 11), they are isolated from the chassis, if you can read any resistance at all, then there may be a cut in the cable some where and it is making contact with the metal chassis. So you are getting close to where the problem is.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Here are the pictures that I forgot to include in my post above. They show the different resistance readings.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

Problem found - just as people found this same problem before. I never saw pictures of the exact failure point in other posts. Therefore, here they are. What a crappy design flaw.

I don't know how this TV ever worked at all.

In the one picture, you can see the protective insulation tape sliding off of the side of the ribbon connector. This is very sad.

You can also see my fix. I used a blade to cut very thin strips of electrical tape to apply to the aluminum chassis point where the ribbon cable folds over top and reaches the connector on the other side. Afterwards, I checked the resistance to chassis ground, much higher resistances now.

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

I powered up, the lights came on. I'm looking at it from backside with the unit face down on my work desk. I put it all back together and start to program channels to find another problem. LOL

I'm wondering if maybe I can loosen up a screw that maybe I over tightened for the clip that holds the panel in.

Either that, or maybe I didn't put the ribbon into the connector quite right. I will try a little later.


Thanks for all who chipped in. Any suggestions for this issue? Anyone correct this before?

[Dgtech]

Re: Westinghouse LD-4680 - no power - seems to be stuck in stanby

I just realized, that was the side with the worse connector. That was the one with the tape peeled off exposing the conductors. I'll play a little with it later on and report back.