Sanyo brightness problem

[HotHead]

Hi
TV model is a sanyo DP42848
It has a brightness problem. You can barely see the image or tv menu. I've tried resetting the colors, brightness, tint ect and still the same problem on any source input.
Seeing i have sound, i can still see the image and the tv does not shut down and after reading some and reading some more would it be logical to suspect the t-con board t420gw01 v2 to be at fault.
More so the ic chip as15-f?
When the tv is on this chip gets real hot! Can't touch it for more than a half second. Is this the chip that controls brightness,color,tint ect? I beleive i read there is a way to test this with a multi meter but i am not exactly sure what to test or what the results would mean.
Any help is appreciated as usual. I have posted some pics as well.

[tom66]

Re: Sanyo brightness problem

The AS15F controls image colour and brightness, in a way, yes.

To test it, you can use your meter to measure the points VGAMA1 through 15 marked near AS15-F chip.

Put your multimeter on 20V mode, and test each point with the red probe on the point, black probe on chassis or other ground point. Then post your results.

[Moreno83]

Re: Sanyo brightness problem

I fixed a Grundig LCD that had the same problem. It were 3 capacitors that were bulged. I replaced them and the screen was good again.

[HotHead]

Re: Sanyo brightness problem

Thanks for the quick replies...
Moreno83, what board were these caps on and where were they located? A visual inspection on my boards show no signs.
Tom66, here are the results from testing the VGMA 1-15.
Starting with 1 and ending with 15
5.82
5.37
5.37
5.37
5.37
5.37
5.37
5.37
5.37
5.37
5.90
6.30
7.31
7.31
7.28
No idea if this is good or bad!?

[tom66]

Re: Sanyo brightness problem

That chip is definitely failed, I have never seen one that bad. The numbers normally should go from about 0V to 15V or 15V to 0V, monotonically (i.e. increase or decrease ONLY.)

[HotHead]

Re: Sanyo brightness problem

Well getting the chip seems to be easy enough. There are numerous sellers. In your opinion would you think there are more faulty parts causing the excessive failure in this ic?
Also if you don't mind me asking another question...why weren't the VGMA 16 through 22 important, I figure they are test points for the same ic?
I guess my big question now is replace the ic(and try my hand at smd soldering) and hope there is nothing else wrong or buy a complete new board(at a higher cost) and hope it functions.
Any advice?

[tom66]

Re: Sanyo brightness problem

My error. If you like you can test VGAMA16 to 22 too. I was thinking of another TV, regardless though the results so far indicate it is bad.

The chips appear to fail without obvious cause - however they do fail a LOT! When working they don't run that hot, about 45C. So it doesn't seem to be temperature.

Removing the IC is the hardest; putting it back on is fairly easy.

[HotHead]

Re: Sanyo brightness problem

You are spot on! 16 through 22...
16. 7.26
7.27
7.24
7.22
6.85
6.83
22. 6.87

Ordered the chip and will wait a long 3weeks. Now like you said the hard part...! Removing the old chip. :-(
Sooo feel like ordering a hot air desoldering station but can't justify the cost. No idea when I'd need it again...but it's tempting. Lol
Gonna look for solutions. I guess I have time.

[bammbammfran]

Re: Sanyo brightness problem

For removing the chip
you can use a plain 1000w heat gun Just cover the rest of the board with a couple layers of tin foil so that you do not heat up and damage the other parts nearby
Add flux to all the pins first, when hot enough, you will see the solder glisten.
Then it can be reinstalled with a good soldering iron

another not so professional method to remove them if you do not have hot air, is cut the pins using a brand new exacto type blade and cutting the pins right at the chip where they enter with straight down pressure and slight rocking of the blade (front to rear not left to right) do one to 3 pins at a time. you will feel and or hear when you go through.
do two opposite sides, then use a soldering iron to move the cut pins from the board
then do the other two sides

[DLinkOZ]

Re: Sanyo brightness problem

I've used the exacto knife method, but with light scoring alone one side at a time (at the top, as mentioned, where the pins enter the IC itself). Multiple light cuts until it breaks through, so as not to push down too hard and cut the board (and possibly a trace). Once all four sides are freed and the body of the IC can be removed, it's an easy task to use an iron to whisk away the remaining legs from the pads.

[HotHead]

Re: Sanyo brightness problem

Ok so I received the ic as15f and swapped it out with the old one.*
I used an exacto and a combination of the two methods mentioned to remove the old piece. First I scored all the legs close to the ic itself and then snapped each one while rocking the exacto back and forth. Went fine until the last leg. Instead of cutting through, the pad came away with the chip. Oops! (note to self, Dont Force)
I ended up following the trace and soldered a wire between both points. Not so easy...those things are darn small!!
I should of snapped a pic or two before closing it up but forgot.*
Tv has been working fine for the past two days.*
I thank you all for the help.*