Philips 42PFL3405H/12 very bright, white picture

[yohnsee]

Hello everyone.
I need a little help from you.
This TV was working fine, up until last week. Then it was not turning on.
I narrowed down the problem to mainboard. As I was unable to solve it on component level, I ordered a mainboard for it. A local guy sold me, from his broken screen set. But in my TV it gives this strange picture, as you can see on the attached photos. I measured the following voltages on the T-con connectors with screen ribbon cables attached and without them.
Vcom: 16.3V
H_vdd: 8V
Tcon_Vcc: 3.3V
Tcon_vdd: 16.5V
Vdd_odd: 28V
Vdd_even: -5.3V
These values are within 0.2V with screen attached to t-con.
Also, there is no change in this symptom if I connect only one side of the screen.
Is there any way to be sure, wether it is LCD screen failure or mainboard?
I am not 100% sure, the mainboard I bought is working fine.
P.S: I checked the service menu, and the display code is right for this set.

[budm]

Re: Philips 42PFL3405H/12 very bright, white picture

Looks like bad Gamma Voltages.
You need to list the Gamma Voltages.
We cannot tell from your pictures as where the T-CON board is.

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Looks like bad Gamma Voltages.
You need to list the Gamma Voltages.
We cannot tell from your pictures as where the T-CON board is.

Thanks, budm. Tomorrow I list the VGammas.
The tcon is integrated onto the main board, 3. picture, upper left corner. From there, the 2 white ribbon cables goes directly into the buffer boards (I hope I say it right, the 2 very narrow, long pcbs on top of the display) from there, only cof goes to the lcd display.

[petehall347]

Re: Philips 42PFL3405H/12 very bright, white picture

i take it you tried turning the brightness down ?

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Yes, I have. I don't have any black on the screen, the startup logo is also the same white-on-even whiter as the rest.

[ducky29]

Re: Philips 42PFL3405H/12 very bright, white picture

Try changing the display code on the service menu and match it to your screen.

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Try changing the display code on the service menu and match it to your screen.

Thanks ducky29, in the first post, I mentioned, that I matched the display code with the sticker on the chassis. Or should I try random 3-digit numbers?

[ducky29]

Re: Philips 42PFL3405H/12 very bright, white picture

Thanks ducky29, in the first post, I mentioned, that I matched the display code with the sticker on the chassis. Or should I try random 3-digit numbers?

Sorry didn't read the whole thing. Looks like a panel fault based on the 2 screen photos that I saw.

Does it change if you let the tv running for some time?

Try the menus, if you look closely, does it leave marks, shadows after closing the menu? If so the panel/ tab bonding faulty.

Or Try a factory reset or a firmware update.

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Looks like bad Gamma Voltages.
You need to list the Gamma Voltages.
We cannot tell from your pictures as where the T-CON board is.

A very big THANK YOU, for putting me on the right track. Indeed, the gamma voltages were wrong. Vgm1 to Vgm5 every reading was the same, 16.2V. So I suspected the gamma IC (U7051) MAX9668. Luckily, I have a donor board laying around, I swapped this IC quick. See photos, this is the result. I call this progress. The left side is perfect, the right side needs more work. If you have any idea, what could it be on the right side?

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Sorry didn't read the whole thing. Looks like a panel fault based on the 2 screen photos that I saw.

Does it change if you let the tv running for some time?

Try the menus, if you look closely, does it leave marks, shadows after closing the menu? If so the panel/ tab bonding faulty.

Or Try a factory reset or a firmware update.

Thank you ducky29, I try every other option before I call it a display failure. I made a small progress, please see pictures above.

[yohnsee]

Re: Philips 42PFL3405H/12 very bright, white picture

Please take a look at these 2 pictures.
I turned the TV over, to make better quality shots.
I don't know, what could be still wrong on that side, but as I see a pattern in the problem, I want to think it is not a bad lcd panel.
Since my last post I've done the following:
Measured every pin on the wrong side with DMM, voltages are the same with screen attached and without. Signal waveforms were not tested.
Swapped U7052 (Level shift IC), no change.
Currently waiting on a new motherboard, to see, whether am I right or not. And because I don't have enought knowledge to solve this on component level (yet).