Samsung GQ50Q60AA and VGH shortage

[kevin_allein]

Hi, have a Samsung GQ50Q60AA, that went into protection. I measured CKx lines, found no problem, but noticed on the left side from the back of the TV, that the VGH had a ~5 KOhm resistance against ground. I cut the VGH trace on the left panel PCB to the Panel and now the TV is no longer going into protection, but shows a picture with a vertical black line and some small horizontal bad lines. Please see the image.
I am a bit surprised, since 5 KOhms do not really seem to be a short.
Obviously now the left (always seen from the back of the TV) part of the panel now has no connection to VGH. I ordered one of those little DC DC convert kits from China to feed in a programmable VGH, but that has not arrived yet. Will that fix that issue ?
I have seen a couple of videos on Youtube for short killers for CKV lines. I guess that should not be done for VGH ?

[nomoresonys]

Something seems wrong, was there a video or or something that suggested cutting the VGH trace?

[kevin_allein]

In the meantime the DC / DC converter boards from China arrived and I tried to install it today. Attached you see the cut of VGH and the new wire, that inserts the VGH voltage from this little China board. On the other side of the TV panel VGH is 24.6 V, so I adjusted that converter to 24.6 V as well. However the image on the screen is absolutely identical.
I performed some more measurements and found something really strange: When measuring the original feed of VGH above the cut I saw a negative voltage, something I would expect from VGL. On the other side of the panel as stated above VGH is 24.6 V. Unfortunately performing multiple measurements I slipped with my probe and a small spark was created. Now the negative voltage is gone, the 24.6 V is still there and the picture still looks like above.
Has anyone ever seen something like this ?

[Diah]

well well well.... yours DIY was just gute.. LOL sadly you killed rail..
but how it come the idea to you using DC to DC... at which Data Freq.. VGH VGL aren't VCC.
go back tracking yours shorted rail from u ribbon to LVDS to MB .. so you bring it back what you are missing and dont forget to uninstall yours DIY

[Diah]

BTW from yours Photo look you have short to chassis between CK2 CK3 test points

[kevin_allein]

There was a little solder spot on that picture, but it did not really generate a short.
I removed the DC/DC converter, but I am confused about your suggestion to "tracking your shorted rail". You mean the one, that was negative voltage before and is now dead ?

[Diah]

You mean the one, that was negative voltage before and is now dead ?

of course this rail what ells ! usually will end at MB if the contact pins of LVDS and U ribbon are fine

[Davi.p]

Don't listen to certain stories, VGH VGL are normal supply lines and the output of a normal dc dc converter..
can you show where did you do this "cut"? I see only a missing diode..

[Diah]

its useless to answer stupid one... then explain to us how the VGL / VGH function via Discharge Pump Converter ( Oscillator ) to switch on off T gate on screen..

[kevin_allein]

on the unmodified TV there is a ESD protection diode and above a golden circle test point. The test point and the pad for the ESD protection Diode are connected by a thin trace. I did cut this trace.

[kevin_allein]

@Diah: I did not understand that last post: "its useless to answer stupid one... then explain to us how the VGL / VGH function via Discharge Pump Converter ( Oscillator ) to switch on off T gate on screen.."
Was that directed at me ?

[Diah]

@Diah: I did not understand that last post: "its useless to answer stupid one... then explain to us how the VGL / VGH function via Discharge Pump Converter ( Oscillator ) to switch on off T gate on screen.."
Was that directed at me ?

its not to you... its to the one who put his nose in this threat.

[Davi.p]

So the test point is connected to the Mountain or valley (lcd panel)

[Davi.p]

frogot the "?"..

[kevin_allein]

Here is a YouTube Video of a similar case. He measures a negative VGH and uses an external DC/DC to supply correct VGH. In his case it fixed the problem. In my case it did not.

https://www.youtube.com/watch?v=Ew74UMLXMwY

[Davi.p]

"Pensonic"?? this is a plague.. it remains "Penis-onic"..

My guess is that these type of faults generates by oxydation on a certain part, before i was suspecting tcon circuitry, after some tests i think different , the degraded part is within the panel, (we can talk about this maybe later..), now the important is that circuit has more resistance than factory product, for the ohm's law you have to increase slowly the VGH to get rid of it until the pixels gate triggers to lit and bright colour.. if VGH is not enough maybe also VDD must be increased.. this is probably not a permanent modify, is to only study the case, when my tired legs responds a bit i will test some also on mine, but the real cure is another.. always my opinion..

[Diah]

"Pensonic"?? this is a plague.. it remains "Penis-onic"..

My guess ..

go guess and bit om soccer or lotto , don't guess on electronic repairt... its always KNOW HOW are

[Davi.p]

Another report to staff, it's incredible you are still here.. these are the users of today.. sadness..

[kevin_allein]

I am pretty puzzled by what I found now: From the 96 pin connector VGH goes directly to R44 and here I still measure 24.6 V. The VGH test point however seems to be connected through a trace to the very left of the scalar board and than directly to the Panel. So it seems like there is a short in the panel between VGH and VSS/VGL ?