Samsung LN32D403E4D - Jumpy/Double Image

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Think this is the device


If it's working, and conducting, voltage between B-E (outer two pins) should be approx 0.7V.

...and it's not a 1117; replacing it with one may cause damage...

Is VSS definitely positive? I suppose it could be what SAMSUNG call VCOM. It would not cause jumpy image.

Jumpy image could perhaps be caused by VGH/VON or VGL/VOFF going bad.

Weird that a 1117 caused no issues and same symptom?

Actually the VSS was a negative voltage -7.43v

What is VGH/VON VGL/OFF?

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

VSS therefore must be VOFF/VGL as I thought. So -7.5V approx is fine for that. Try and find the +20V to +30V supply. It will be on there somewhere.

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

VSS therefore must be VOFF/VGL as I thought. So -7.5V approx is fine for that. Try and find the +20V to +30V supply. It will be on there somewhere.

Would it be labeled something?

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Yes.

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Found these:

VONE: 27.6v
VOFF: -11.3v
VSS: -7.43v
HAVVD: 7.50v

All tested with original N2 diode back in

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Any good? Also, why can't I find more than one tab bond on this. Doesn't make sense there'd only be one for the entire panel

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Those look reasonable.
I'm guessing it's an unrepairable fault.
As for one bond, it's a new direction LCD TVs are going in. All the panel drivers (all 4,098 columns) fit into one bond now to save money.
Previously I've seen as few as two, never just one until now.

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Ah. Why do you think hitting that diode with the freeze spray caused the image to attempt to go normal?

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

It's not a diode, it's an NPN transistor. Perhaps you were cooling the tab too? I forgot about that, it is odd. Would help to get a scope out and check the various signals.

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

I directly cooled the tab too and picture was only affected by cooling the transistor. Don't have a scope

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

What happens to VOFF and VONE if you cool that transistor?

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

VOFF: -18.54 when sprayed and quickly goes up and stabilizes to -11.37
VONE: stays the same when sprayed at 27.6V

Voltage drop across the transistor from B to E is -0.6v

Also when the voltage at the base of that transistor drops to -6.67v is when picture is 85% better (when freeze sprayed)

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

I'm tempted to try adding a resistor before the base of the transistor to drop the voltage down to around -5v and see if that gives a better picture? Lol

[newtothis]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Its worth a try

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

How would I calculate right value resistor to use?

[newtothis]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Oh I am sorry I am having a bad day and not thinking.

A resistor will not work... Resistors reduce current not voltage.

To drop voltage you need a regulator

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Actually a resistor could work by loading down that output. But I would only consider that a temp fix and replacing that transistor is likely the permanent solution.
So, -18V, picture poor (expected: very lucky LCD panel doesn't fry!) and -11V, picture OK? Or other way around?

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

Other way around, -18v when it's cooled and the picture is trying to rejoin into one image

Is that transistor definitely bad? I measured -0.6v across base and emitter

[tom66]

Re: Samsung LN32D403E4D - Jumpy/Double Image

That is well beyond what I would expect for most LCD panels! It is possible this Samsung does it differently but I would be surprised.

If you have an NPN through hole transistor lying around you could probably do a quick check and put it in place of the existing one. Link to the datasheet and we can see if it will work.

[ohmmy]

Re: Samsung LN32D403E4D - Jumpy/Double Image

So I have no idea what happened, but now the picture is way worse!

The gamma chip is super hot to the touch now but the measured voltages from it aren't all over the place, they give steady lows/highs

If I cool that same npn transistor now, there's no affect. Here's a pic