Samsung LN37A550 Repair

[vinder1]

Recently my Smsung LN37A550 has developed a problem where the picture starts to fade to white and I am hoping one of the forum members can kindly help me make a preliminary diagnosis. The tv starts normal and the picture is fine for several minutes before the picture starts to fade as if a heavy fog came in. You can still see the picture but it is now obscured by this white haze. Sometimes the picture goes back to normal after a while but always reverts back to the white haze. Turning it of and then on again it will start normal but soon the problem will come back. The only other symptom is that the TV has been difficult to turn on using the remote in the weeks proceeding this problem. This weekend I plan to start taking it apart to check if I can diagnose the problem. I would greatly appreciate any advise your forum members can provide to help me solve this problem.

Best Regards
Al

[stj]

Re: Samsung LN37A550 Repair

open it, take good foto's of all the circuit boards.

[tom66]

Re: Samsung LN37A550 Repair

This looks like it could be a gamma IC fault, can you supply a picture of the T-con board? The difficult to turn on problem could be unrelated and caused by bad capacitors.

[vinder1]

Re: Samsung LN37A550 Repair

Tonight I opened the TV up and all I see is two bad capacitors on the power board CB852 1000 uf ans CM859 470 uf. I also took pictures of the boards for the board members to review. I was not able to detect any damage to the boards but I am not an expert. Any advice on how to proceed would be greatly appreciated.

Best Regards
Al

[budm]

Re: Samsung LN37A550 Repair

OK, on the top right of the T-CON board by the connector, there are test pads for testing the GAMMA Voltages: VGMA1~22. Please take the DC voltage and list each readings for us to see. I suspect U201.

[vinder1]

Re: Samsung LN37A550 Repair

Thanks for your reply. As requested by budm Below are the voltage readings for the VGMA test pads.

12v pin into T-con board 11.64 v

VGMA 1 15.57 v
VGMA 2 15.46 v
VGMA 3 15.38 v
VGMA 4 13.05 v
VGMA 5 11.98 v
VGMA 6 10.80 v
VGMA 7 10.18 v
VGMA 8 9.99 v
VGMA 9 8.43 v
VGMA 10 8.20 v
VGMA 11 8.05 v
VGMA 12 6.65 v
VGMA 13 6.59 v
VGMA 14 6.31 v
VGMA 15 5.05 v
VGMA 16 4.82 v
VGMA 17 4.35 v
VGMA 18 3.56 v
VGMA 19 2.90 v
VGMA 20 0.51 V
VGMA 21 0.38 v
VGMA 22 0.32 v

Please let me know if this makes sense and if any other information is needed.

Best Regards
Al

[tom66]

Re: Samsung LN37A550 Repair

It does appear that the gamma IC is bad i.e. U201 as budm said. If you are good at surface mount rework, replacing the IC is easy. Otherwise, you will have to get your T-con repaired, or replace the T-con with a new/used part.
I would also replace the bad capacitors as while they are unrelated to the image fault, they will eventually fail completely stopping the TV from powering on at all.

[vinder1]

Re: Samsung LN37A550 Repair

Thanks for the help. Yes I think I can do the repair but I am still trying to find the IC on the board. Please let me know where it is located.

Best Regards
Al

[vinder1]

Re: Samsung LN37A550 Repair

Sorry I just found it. Is their a part number for this IC? Their appear to be no numbers on the chip

Best Regards
Al

[tom66]

Re: Samsung LN37A550 Repair

You will first have to remove the pad over it, then clean the top adhesive with a little isopropanol. Typically, the part number is something like AS15-F, and all AS15 chips will interchange with each other. You can buy them on eBay for a couple $ each.

[vinder1]

Re: Samsung LN37A550 Repair

Thanks tom66. when I lifted the thermal pad (not sure if this is for cooling) it came apart and lifted the numbers of the chip. So I will look for AS15-F and that should work.

Best Regards
Al

[tom66]

Re: Samsung LN37A550 Repair

One trick for revealing the numbers is to use a piece of chalk and draw on the IC. The numbers should appear in the chalk.

[vinder1]

Re: Samsung LN37A550 Repair

Thanks tom66. Unfortunately the chalk did not work. Maybe somebody knows the exact chip number?

Best Regards

[tom66]

Re: Samsung LN37A550 Repair

This post:
https://www.badcaps.net/forum/showth...light=LN37A550

seems to indicate it is an AS15F chip

[budm]

Re: Samsung LN37A550 Repair

Same as this one:
https://www.badcaps.net/forum/showth...ng+LN37A550P3F

[vinder1]

Re: Samsung LN37A550 Repair

After replacing AS15-F on the T-con board and replacing the caps on the power board I put the TV back together but unfortunately this time their is no picture at all just a black screen. Sound is no problem and the channels are there. A friend of mine who replaces chips everyday did the AS15-F for me and I am pretty sure He did it right. Any ideas on what may have gone wrong?

Best Regards
Al

[budm]

Re: Samsung LN37A550 Repair

Do you still get the backlights? Also re check the LVDS cable and the fuse and the voltage on both ends of the fuse on the T-CON board. Something was not done right some where.

[Shinju]

Re: Samsung LN37A550 Repair

Or the chip is defective as we have seen in the past here

[vinder1]

Re: Samsung LN37A550 Repair

Thanks for the replies

The backlight is still working and I detect 12v at the T-Con board where the cable attaches. At the connection I checked the test pads and all show a voltage 1.07 to 1.27 v and a bit higher on the second row 1.21 to 1.45v not sure where the fuse is located. Nothing on the board looks like a fuse. Any help locating it would be appreciated. The 21 check pads for the gamma IC have similar voltages as before the IC replacement. The chip could be bad and I could replace it again if necessary. Any help would be appreciated.

Best Regards
Al

[tom66]

Re: Samsung LN37A550 Repair

Looks like the gamma voltages are still bad, it is possible you got a bad board/chip.