Samsung PS50a410 - no picture

[turbzz]

No Picture - just back lite



Have check PS voltages etc all are good

the logic board is blink ok

If you pull the top three ribbons on the Y sus you get the usual black half screen and the same goes with the bottom no dancing colour box etc like if the buffer boards were gone.


Thought it may be the eprom needs to be reset ---- just a thought??

If so how should this be done



Other than that any suggestions??

have another with the logic board not lighting up or blinking?? can these boards be repaired?

Cheers

[tom66]

Re: Samsung PS50a410 - no picture

Do you get any light from the screen in a dark room?

Are you saying when one of the boards is unplugged you get a picture on the other half?

It is common to sometimes have only a lit screen or scrambled picture on one half if one board is removed, because the boards are synchronised.

[turbzz]

Re: Samsung PS50a410 - no picture

Yes the screen is back lite you can see it come on when you start up but no picture has sound

Yes when you unplug the three top ribbons you get a black top screen not the lite screen and visa versa with the bottom three cables to the y sus board to the left hand side of the tv looking from the rear

Normally if you do this to a buffer board you get picture when you unplug the faulty one

all the voltages check out so Im at a lose



any other samsung plasma is a bit easier to diagnose. had a few of these and always at a loss


if you normally do this on a

[tom66]

Re: Samsung PS50a410 - no picture

You may have a Z-sustain/X-main issue. Do you get sound?

[turbzz]

Re: Samsung PS50a410 - no picture

Yes have sound

will change chanells blind etc

all voltages are good would it be a mofset

[turbzz]

Re: Samsung PS50a410 - no picture

there is sometimes a buzzing from the ysus

[turbzz]

Re: Samsung PS50a410 - no picture

ps thanks tom for the posts

[tom66]

Re: Samsung PS50a410 - no picture

Try plugging in a known working DVD player with playing DVD. Press Input until you get sound. Make sure to plug in the video cable as well as audio - most Samsung TVs won't make any sound without video.

[turbzz]

Re: Samsung PS50a410 - no picture

Yes am getting sound but no picture as well

[tom66]

Re: Samsung PS50a410 - no picture

Good. This means the X-main is most likely the issue. There is one further check you can do. Do you have a digital multimeter?

[randtek]

Re: Samsung PS50a410 - no picture

Here's a trick that may help you. It will immediately tell you if you have a main board problem, or a panel drive board failure. You said the LED on the digital board is blinking good, so this is a pretty good indication that your digital board is functioning properly.

1) Unplug the TV from AC.
2) Disconnect the power supply cable going to the main board at the main board end.
3) Look at the legend on the power supply board to determine which pin is PS-ON, usually pin 1. Stick a wire in this pin of the connector cable you disconnected from the main board, and short it to ground.
4)Disconnect the LVDS cable going from the main to the Digital board.
5) On the digital board find 4 test point pins sticking up from the board in a square pattern, about 1/8" across. Short these pins together.
6) Plug the unit in to AC.

This process will generate test patterns from the digital board. If you see the test patterns begin to cycle on the screen, you know everything is working properly except your main board. If you do not see the test patterns, you have an issue in the panel drive circuitry.

[tom66]

Re: Samsung PS50a410 - no picture

Thank you for that trick Randtek - I've never heard of that before (then again, I've only repaired one Samsung plasma, the other four were LGs and one was a Panasonic.)

[randtek]

Re: Samsung PS50a410 - no picture

You're welcome Tom. There is a similar technique for LG plasmas. The only differences are, there is no need to ground or otherwise connect to any pins of the power cable connector, and instead of 4 pins on the digital board, there are 2 holes in the digital board that are test points. They are labeled "Ext-Gen" on most sets. These holes get shorted together, and then plug in AC. It can be tricky to short the holes, and keep a reliable connection, so we have a tool we devised for the LG sets. It consists of an old alligator clip, and two small pieces of wire soldered into the ends of the jaws. See the image below.

[turbzz]

Re: Samsung PS50a410 - no picture

Good. This means the X-main is most likely the issue. There is one further check you can do. Do you have a digital multimeter?

Yes do have

we repair alot of samsungs but this model has me stumped everytime


as for Randtek thank you for your insight

with the digital four pins do you keep it shorted together whilst power is plugged back in?

Cheers

[turbzz]

Re: Samsung PS50a410 - no picture

The other set is the same model but had a vertical line down the panel at the fourth ribbon though it is not showing any picture now either no blinking on the digital board

[tom66]

Re: Samsung PS50a410 - no picture

Since you service a lot of these TVs do you have a scope?

[turbzz]

Re: Samsung PS50a410 - no picture

yes

though Im having issues with it at the moment

hence the questions here

[tom66]

Re: Samsung PS50a410 - no picture

yes

though Im having issues with it at the moment

hence the questions here

If you do get it working, check the Z-drive FFC and the Y-drive waveform. You should use a 10X 600V rated probe and set your scope to 5V/div (50V/div at 10X.)

[randtek]

Re: Samsung PS50a410 - no picture

Yes do have
With the digital four pins do you keep it shorted together whilst power is plugged back in?

Cheers

Yes, that tells the digital board to generate test patterns. Remove the shoret after unplugging the set when you have completed the test.

[turbzz]

Re: Samsung PS50a410 - no picture

No test patterns on either unit

there is no lvds from the main board / power supply to the tcon/ digital board