Samsung 933HD stripes in image

[magneh]

Hello,

I have a Samsung 933HD with weird stripes in the image.
First two pics were taken with some seconds of difference, and we can see that the stripes change.

I've checked the voltages of the power board, they are all OK.
I've also disconnected the screen from the mainboard, and the bulbs and inverter are OK, as the screen presents itself white and with no picture as supposed.

The problem should be in the mainboard probably.
Can I mesure voltages in LVDS connector to troubleshoot?
Maybe those IC's with alu dissipators are the source of the problem...

Any thoughts?
Thanks!

[tom66]

Re: Samsung 933HD stripes in image

Do the stripes move for any given image, or are they fixed?

[magneh]

Re: Samsung 933HD stripes in image

Do the stripes move for any given image, or are they fixed?

Mostly they are fixed ... just some lines change but 90% are fixed. (depends on input, as you can see the stripes are different in this photo compared to Ext1 as in 1rst picture of 1rst post)

Another photo added with TV tuner selected.

[magneh]

Re: Samsung 933HD stripes in image

Hello again!

Should I consider mainboard is bad and try to get a new one?
Or is it a waste of time and should I scrape lcd and power supply and forget it?

[magneh]

Re: Samsung 933HD stripes in image

Well, since I dont want to spend what people ask for a new mainboard,
I removed the heatspreaders to see the IC's underneath it.

the 2 smaller ones are samsung memory chips, and the bigger one a Samsung DNle BGA.

Could this BGA be the issue?
Connected the power supply with mainboard and power button, and without screen so I could mesure some points labeled.

Dunno if it's due to the fact of the screen not being connected, the 5V panel didn't present.
Also mesured the voltages on the points nearby , all 0V.

The set turned on without the screen connected, but didnt turn off. Had to unplug it.

Any thoughts?

[magneh]

Re: Samsung 933HD stripes in image

UPDATE:

Now I connected the lcd to see if there was any difference, and the screen didnt light up.

The bigger heatspreader was hard to unglue ... did I damaged something when removing it?
Weird ... now the set doesnt power off pressing power button and the screen doesnt light up...

All 5.1V and 15V were present on the powerboard , just checked it.

[tom66]

Re: Samsung 933HD stripes in image

My guess, LCD panel is bad.

[magneh]

Re: Samsung 933HD stripes in image

It was "good" before removing the heatspreaders...

At least it turned on with backlight and image with problems as in the photos...

Figured out that it turns on on the button of the set but doesnt power off ...

But with the remote it turns off! weird...

[tom66]

Re: Samsung 933HD stripes in image

What I meant is the previous symptoms with the lines. That is almost always caused by bad LCD panel if the lines are mostly static.

[magneh]

Re: Samsung 933HD stripes in image

What I meant is the previous symptoms with the lines. That is almost always caused by bad LCD panel if the lines are mostly static.

Ok.

But this issue now with the screen not even lighning up, is it the mainboard that gives the command to turn the bulbs on?
Or the power supply should do it by herself , even if main is NOK?

Now I even dunno if the power supply is still good...

[tom66]

Re: Samsung 933HD stripes in image

The main board will send PS_ON, to turn the power rails on, and then BL_ON, to turn the backlights on. In some small monitors sometimes there is only one ON/OFF signal which turns on both backlight and power, or the power rail is always on.

[magneh]

Re: Samsung 933HD stripes in image

The main board will send PS_ON, to turn the power rails on, and then BL_ON, to turn the backlights on. In some small monitors sometimes there is only one ON/OFF signal which turns on both backlight and power, or the power rail is always on.

How can I find the BL_ON signal?
What I can understand is after removing heatspreaders, mainboard stopped sending BL_ON to the power board.

Correct?

[tom66]

Re: Samsung 933HD stripes in image

Yes, that would appear correct. Is there a legend on the other board? Maybe indicating what pins what supply/signal is there.
BL_ON can also be BK_ON, ON/OFF, BLON, BL, VBL.

[magneh]

Re: Samsung 933HD stripes in image

Yes, that would appear correct. Is there a legend on the other board? Maybe indicating what pins what supply/signal is there.
BL_ON can also be BK_ON, ON/OFF, BLON, BL, VBL.

It could also be BLEN?

[magneh]

Re: Samsung 933HD stripes in image

Hello!

Mesured BLEN and I have 0.01V ... not good.

Is it possible to find a schematic of this mainboard?
Or should I just try to follow the path of this signal ?

Thanks for any inputs!

Cheers!

[selldoor]

Re: Samsung 933HD stripes in image

It is not good if the BLEN is supposed to be pulled high for ON. If is pulls LOW for ON then
there is another problem.
Suggest you disconnect the main board and test again to see if it starts as high.
If it starts as LOW then with a 300-500 ohm resistor jumper 5v to BLEN and see if they come on. ( On some sets you also have to jumper DIM to 5v using a resistor.

Chances are that Tom is correct in saying the panel was bad and now you have probably
partly pulled the chip with the heatsink off the board.

[magneh]

Re: Samsung 933HD stripes in image

Ok , so I've traced down BLEN signal, and it comes from a resistor I think labeled 472 (mesured 4,71k oHm) who connects to IC1022.

5V are present on IC1022, and appear on one side of resistor (?) 472, but on the other side (before pin of BLEN) I only get 0.01V.

Here's a photo with these points and tensions.

EDIT : Mesured values @ startup , it allways shows 0.01 from the moment power supply turns on in BLEN pin

[tom66]

Re: Samsung 933HD stripes in image

That would appear to be a "pull-up" resistor. It is tied permanently to a 5V supply. Then, it is controlled by the nearby transistor Q1012. When that transistor is turned ON (base-emitter >0.6V) the BLEN signal will be pulled low, turning off the backlight. (This is an inverter circuit.) The resistor adjacent, also 472 value (4700 ohms) should be checked. Voltage on the end closest to the transistor should be ~0.6V with BLEN off (0V), and 0V with BLEN on (5V)

[Shinju]

Re: Samsung 933HD stripes in image

Have you tried a heat reflow? not sure why one would want to remove the heat sinks from the chips but my guess is something got damaged in that process as someone has stated.

[magneh]

Re: Samsung 933HD stripes in image

That would appear to be a "pull-up" resistor. It is tied permanently to a 5V supply. Then, it is controlled by the nearby transistor Q1012. When that transistor is turned ON (base-emitter >0.6V) the BLEN signal will be pulled low, turning off the backlight. (This is an inverter circuit.) The resistor adjacent, also 472 value (4700 ohms) should be checked. Voltage on the end closest to the transistor should be ~0.6V with BLEN off (0V), and 0V with BLEN on (5V)

Hello!

Well picked up some readings.
The resistor seem OK .

For what I understood , I got 0.7V on the end closes to the transistor, and then it's normal to have BLEN off right?
Which element would be responsible to push those 0.7V to GND, having BLEN ON?
Thanks!