Samsung LE37B551. White picture

[Davy]

Have Samsung LE37B551, you can just about see the picture and on-screen menu but they are far too bright.

The PWM on pin 3 to the inverter from the main board doesn't alter any, voltage or waveform when viewed on a oscilloscope no matter the brightness setting.

Checking on the bench it did fire up OK a second or two then gradually turn to 'excessive white', just like some CRT screen faults.... it only did this once.

Anyone know how to reset the CPU and if a manual is available thanks.

Dave

[Turnip]

Hi Davy,

Wonder about the screen used, as some are a bit suspect with this problem, but not usually 37 inch so far.

Chris.

[downunder]

Hi Davey,

That sounds like a faulty gamma chip on the T Con.....AS15G, H, or U. Remove the T Con cover and see if it's got one, a smallish 48 pin postage stamp. A very common fault on a host of brands. Not easy to replace unless you've got good soldering skills, otherwise a replacement T Con could be the go.

Bruce

[Davy]

Hi Chris and Bruce, thanks for quick reply.

Dunno what brand the screen is it's on my mates bench, he's not a TV engineer, can only see a couple of components on the Tcon, the bottom assembly needs be removed to get at.

I'll have a look tomorrow when I pop round, must be loads of Tcon boards kicking about, might even have one myself, well and truly buried in this set.

I thought with no PWM activity voltage or waveform wise from the main board to pin 3 on the inverter/psu board (all in one) when the brightness is altered.

Chris, when you say screen are you meaning when a part of it goes dark? I've never come across this fault myself..... could be a clue here if I say the picture does look ghostly no doubt one of you guys are right.

Thanks again for your help, I appreciate it.

Dave
 

[downunder]

Hi Davey,

I get your drift, T Con is under the pedestal mounting hardware.
Can see the CCFLs being turned on to such brightness levels as to cause an over-bright picture. The inverter protection senses average current used by the CCFLs and would activate protection.

My money's still on the gamma chip.            Bruce

[Turnip]

Hi Davy,

Would agree with Bruce if I knew what he was on about - He's so technical for an Aussie.

Only mentioned as small screen versions are well known for panel problems - Chris.

[Davy]

Had a good look at it, and the PWM does work as it alters the back lights when you adjust the back light setting - ain't the brightness as I thought, altering the brightness makes no difference at all.

Still dunno what screen it is, studying the picture, guess I could describe it as 'milky' the contents being being very feint, and the blue just about distinguishable so guess I too will got for Bruce's suggestion on swapping the Tcon.... changing the chip should not be all that difficult, noted there's some SMD electrolytic's on the board seeing them makes me think another board is more viable.

Thanks for the 'heads up' I appreciate it, let you know when I can get my hands on a Tcon or swap the chip.

Regards all, Dave

[Davy]

Bruce is spot on... t'was the gamma chip, thank you all and regards

Dave