Led tv Polaroid MHDV3911-s7 Half an image

[Karn]

This is my first post, although many of you have already helped,me fix a few plasma's with blown caps etc.by following other posts, but I thought
I'd try and fix this led tv, but I am in need of guidance.

Tv Model Polaroid MHDV2911-s7 39"LED TV

Inside back cover chassis label T390HVN01.0 /MA3394233100014

Power supply board TV4205-ZC02-01 / KB-5150 / M16/G42332/02

Main/Av board MSDV3223-ZC01-01

Bottom buffer boards VP3A25B02FZZ-281100 1309 T390HVN01.0 / T390HVN01.0 XL / FX-5539T01S02-32F-0000N0P-00509-07

I believe both JVC LT-40C540 and Panasonic TX-39A300E are similar/may share same boards ? Cheap tv

Problem as can be seen in first photo is that the right side of the screen, when looking at it appears black/ no picture but backlight is showing but no image.
Left hand side of screen shows menu image with vertical lines present.This is all whilst no signal connected to the tv.

All I have done so far is disconnect ldvs cable from main /av board to lower buffer board. This gave me 2 seconds to black across the screen.

I then disconnected the left hand side connector to the bottom buffer(brown flexible cable ? Lvds?)
This gave a whiter screen, with less noise in it but still with some vertical lines present.(see photo)

No further testing has taken place as I cannot find a service manual online?
Please advise me on the following and correct my lack of knowledge in trying to fix it, I thank you all.

Does it appear that this screen is ok/or possible tab problems?(guessing this from vertical lines?)

Is there a t-con board hiding somewhere or is it built into bottom buffer boards? I guess this from following the cable from main /av board? am I correct?

Looking at the many pathways on the av/main board, pcb under the heatsink to the lvds cable to the bottom buffers , I guess I need to test that
(a) the signal & power is being generated on this board &
(b) it is then going from the bottom right buffer (where there is a splitter cable) to the bottom left hand side buffer board.

I see many test points on the bottom buffers boards, VGA8/VGA9/SDA_GM/FLP1/Ycomu etc. but I am lost as what voltages and what I am looking for and which to test etc, can anyone help me gain more knowledge. I do have a cheap mm and smart smd tester, plus peak atlas esr tester & scr tester and also a hot air station, but still very much a beginner in all of this apart from fixing a few blown caps etc.

Please ask if you need any further images, many thanks in advance Kris.

[tvtimmy]

Re: Led tv Polaroid MHDV3911-s7 Half an image

The panel is bad.

[Karn]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Thanks for the quick reply tvtimmy. Can anyone advise to further my knowledge if I am correct in thinking the following ;

(a) the image signal & power is generated on the av/main board for this tv

(b) that ldvs signals are going to the first bottom buffer board, but are not then being shared to the other bottom buffer board? Could be power signal to this buffer? hence lack of any image on one side.

Many thanks chris

[angelos]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Some panels get a +12V supply to that board that is attached to the screen. This aught to be the timing control board. On this board Other voltages are generated for the COF IC's to operate correctly. I know that you get VGL and VGH and these are normally VGL= -6V and VGH=+26V, This is mainly for your grey scale. Then there is Vcom etc. On some manufacturers boards these test points have different names like the VGL would be called Voff and VGH would be Von.
Just maybe you have a surface mount cap somewhere on your TCON board that is short circuited causing a voltage drop but most times it failure of those COF Tab bonds, those IC'S on the ribbons.
To zoom into the test points on the panel you need to get the input of more experienced ones on this forum. Good luck..

[Karn]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Many thanks for that information Angelos, thats the sort of knowledge I need to know. I will have to examine these bottom buffer boards closely to see if there is anything visible blown & if there are the same test points on main/ av board, right bottom buffer & left bottom buffer.

I am probably wrong, but I am thinking signal and voltage for timing is getting to the right buffer but after that it all goes wrong, where the signals split & thats why I only have image to one side?

If anyone has a manual showing these test points I would be most grateful, just trying to improve on my fault tracing abilities.

[Andrew F. Ali]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Even if you get the signals and voltages back up to sent to the dark side of your screen and per chance you do get a full image. The other side has those vertical lines that would still be visible and so you would not have a TV that would be friendly to the sight for easy viewing.

[Karn]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Hi Andrew, now its been confirmed that its a bad panel, its just a case of how far I can try and trace any faults, like blown smd components/cof etc. on the bottom boards, as I know one side is receiving the signal it would be nice to be able to trace it to the faults. Now its more of how much this tv can teach me .
Having no schematic and voltage readings makes it so much harder, I suppose I will have to try and see if there is any difference in voltages /if the signal spits before the bottom buffer boards, as I am now guessing it perhaps splits on the main/ av board before going to the ldvs cable? Wish me luck,any help appreciated, Kris

[Andrew F. Ali]

Re: Led tv Polaroid MHDV3911-s7 Half an image

OK. I now understand. Yes this is a good way to learn. Feel free to ask me and the forum any questions you may have to assist you. Good luck.

[Karn]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Many thanks, well I am stuck on where the t-con & power signal is generated from? If you look at my av board photo, you will see a big heatsink & I guess chip underneath, leading to the left,the ldvs cable to the bottom buffer boards. I am thinking I need to start testing here, I think it shows C111 to C 136 on the connector/pcb traces. Anyone like to guide me here?

Have seen Budm's guide on t-con boards so know I shoulds be having some different voltage reading etc. Will have to remove av/board to see if legend underneath?

Its the first tv I have opened that doesn't have a visible t-con board and no schematic. I think they are just a cheaper re-badged tv. Can anyone identify from the chassis id or say if the JVC/panasonic schematics are similar?

Cheers Kris

[Karn]

Re: Led tv Polaroid MHDV3911-s7 Half an image

Just a quick update to all the techs that new what was going on here. Yesterday I had an hour to spare so I thought I would go and test voltages from main to bottom buffers, having found some AUo pdfs for the lvds outputs etc. I thought I would also take a closer look at the cof/ tabs as thats where I was directed to by most people. So on taking a closer look , I could see what appeared to be damage to the cof/tabs. Zooming in on my phone and then later with a hand scope I could see damaged & broken tracks?
If you look at my photo's, I believe this was caused by the broken screw mounts to the back panel, when I first took this tv apart I noticed it had been opened before and a few of the screw mounts were missing ? so I guess someone tried to tighten them and snapped the plastic inside the tv, which rotated on the screw and crushed the novatek cof/tabs?

But thats not all,so I obviously disturbed the cof's/tabs and so on switching the tv on to check the 4 12 volt signals on the ldvs from main to bottom buffers. I smelt burning and quickly shutdown, but not before I had blown fuse F1 on the bottom buffer & I think a few other smd's lol

So the tv will go into my spares cupboard or be converted into a light box.

Many thanks to everyone for their help, until the next time Kris