Samsung LE37A656A1F goes to white screen after 2 minutes!

[cheeky2]

I have a Samsung LE37A656A1F which the screen goes white after a couple of minutes.
 It has the T370HW02 V6 screen in it.
 So far i have removed tcon connectors and powered up board for around 10minutes and then reconnected after powering down to prove whether its the main board (still takes around 2minutes for screen to go white).

 So its looking down to either the TCON or the panel.
 I have heated up the individually the IC's on the tcon board without any difference.
 
 I know the AS15-F IC can fail on the tcon but normally you get solarisation of the colours, but not having much experience with this issue before i am seeking advice on the issue?

Thanks :)

[zomikula]

Does it display a picture before going white.
Is the as15 chip getting hot ?
And how are the vgamma volatges.

When it goes out does the display fade out.. lighter and lighter ?

And are you saying that it goes white with out the tcon connected?

I would say the as15.. it does make the display go white too.
Normally you can see a faint image.

[cheeky2]

Initially the picture of the screen is fine then gradually gets white. The AS15-F doesn't get hot and i haven't checked the voltages yet.
 What should the vgamma voltages be roughly on all test points on the tcon board? I ask as it will be easier to work out for future reference if i have a similar fault in future.
 Thanks

[Turnip]

Hi Cheeky,

Usual to replace the AS15-F as always first suspect for most anything in display problems, and at less than a quid it's cheap.

Admit had a few where the screens were faulty with whiteout with not an AS15 in sight - Mostly small screen stuff with T-con incorporated into screen - Chris.

[downunder]

Hi Cheeky,
Undoubtedly the gamma chip. Could be AS15 but I've come across some AS19. They are not interchangeable.

If you have VGAM test points, say VGAMA1 to VGAMA22 (usually in a group together), you should measure a gradual increase or decrease in volts in the range say 1V to 15V as you check each TP in numerical order. If one or more voltages don't fit this pattern,
the gamma IC is defective. eg 1V, 1.8V, 2.3V, 2.7V and so on is good, but 1.8V, 0.9V, 3.7V, 2.7V is bad.

The gamma IC doesn't necessarily get hot to be faulty, but in some cases it does get too hot to touch.

Bruce

[cheeky2]

Great thanks Bruce for the information :)
 I haven't removed or replaced any as15-f ics so far so prefer to make sure before going ahead and replacing it. If i need to remove ics i tend to use a sticky aluminium foil and screen the surrounding components from the hot air gun! Then use isopropanol to clean up afterwards as the glue underneath the foil leaves a residue.
 
Having that info will certainly help quickly diagnose any future issues as well.

 I will let you know how it goes and results of vgama test point results

 Have a good week and be lucky :)

regards Anthony

[Davy]

Had this with another SammySung model t'was the T'con board.... if you don't want to change the chip Emos will repair the board for you..... they charged around £30 including 1st class post see http://www.lcd-plasma-parts.co.uk/  Be sure to quote the board number.

Dave

[cheeky2]

Thanks.
 I did see that they repair them when looking for a replacement tcon board for it. I will be testing the board later on today.
 Well the results were pretty conclusive!
The first 1-7 pins were between 15.24-14.93
pins 8-14 went from 6.64- 6.49
 The thing was i could see the voltages gradually creep up from the first 7 pins as the screen started to go white!
 Reading the comments below i am going to have a go at it as I am sure i can do it :)

 Thanks for the encouragement as i was just about to send it off!

[Turnip]

Hi Bruce,

Surely change the chip first then theorise later.

AS15  series have most always been the problem with T-cons using this chip.

Mind you, have also read 'pin voltages', but the chip is mostly always duff - Hot or cold.

Quicker to replace it and see how it goes, takes 10 minutes at best - Chris.

[downunder]

Pravda Chris,
What you say is true, but replacing the AS15 is not one of the joys of my life. Don't mind some other kind of chips though.

Bruce

[Turnip]

Hi Bruce,

You're perfectly right as ever, and I avoided having a go 'till I had a whole pile of duff ones to practice on, as new Sony ones are pretty cheap from China, though 'Sammies' sadly aren't.

Didn't much like the idea of hot air gun and tape, though with experience guess it's the quickest way. I currently use liquid flux and solder wick then lift each pin, mind you, all 48 pins take a minute or two.

Clean the board, use a spot of 'super glue' to hold new chip in position - Have a minute or two to get it right B4 the glue sets. Flood area with flux and try 'drag solder' then clean up with solder wick.

First time I tried it, discovered 6 shorted pins on a pin-to-pin check, where could see no solder bridges with the USB microscope - Second one was exactly the same, so hopeful - Chris.

[downunder]

Hi Chris,

Is that what they call British ingenuity? Way too gentle for us colonials. We just heat the IC until you can flip it off with a pointy thing.

Bruce

[Turnip]

Hi Bruce,

Guess you're right, but some of us Brits do things just a pin at a time, as when we go in full force, troubles always ensue.

Guess we're doing the same currently, with the odd bomb here and there.

Suspect outcome dubious, as ever.

Glad just try sort T-Cons - Only faith to try sort 'em - Chris.