Samsung LE23R32B picture fading to white very slowly

[Dannyx]

Good day folks. It's been a while since I've repaired a TV, so now I've got this small one I need a bit of help with. As the title says, the problem is that after it's been on for say 10-15 minutes, the picture begins to very slowly fade to white until it ends up looking really washed out and gray. I took the cover off to get to the t-con board, which is a t230xw01 and immediately noticed the very poor thermal design: at first I thought the metal piece that covers the t-con would also act as a heatsink, like in many other TVs, but no - it's just a piece of metal that stays over the circuit board and doesn't actually contact any of the parts to dissipate the heat, making it pretty much pointless. My main suspect is the AS04-F IC on the right hand side of the board, since it very much appears to be a gamma issue which is very common and often caused by failing ICs in the AS family. What do you guys think ? Cheers.

[dick_barton]

Re: Samsung LE23R32B picture fading to white very slowly

Have you tried blowing air over the chip on the tcon and see if the picture stays. Use a fan or hair dryer set to blow and no heat.

[Dannyx]

Re: Samsung LE23R32B picture fading to white very slowly

Have you tried blowing air over the chip on the tcon and see if the picture stays. Use a fan or hair dryer set to blow and no heat.

No, I have not tried that exact method, although it did cross my mind and did something similar: I took a piece of scrap metal and a relatively thick thermal pad and sandwiched this whole contraption between the chip and the metal cover that goes over the T-con in hope it would dissipate just enough heat to solve the issue...I don't know if it did any good though, because the problem seemed to occur after the same amount of time.

[dick_barton]

Re: Samsung LE23R32B picture fading to white very slowly

It may not be that chip but you could be right that it is a problem on the tcon so perhaps you could narrow down the problem using the fan/air flow.
It may be losing one of the voltages Vh, Vl, Vref etc.

[attainteddragon]

Re: Samsung LE23R32B picture fading to white very slowly

you could also try disconnecting one of the ribbon cables that goes to the lcd panel and see if the screen still fades out. if it still happens, reinstall the side you disconnected and try the opposite side and check again.

[Dannyx]

Re: Samsung LE23R32B picture fading to white very slowly

you could also try disconnecting one of the ribbon cables that goes to the lcd panel and see if the screen still fades out. if it still happens, reinstall the side you disconnected and try the opposite side and check again.

Good call...I guess the idea is to find whether something messes up on the buffer boards.

[dskall]

Re: Samsung LE23R32B picture fading to white very slowly

If gamma problem post your vgm voltages 1-10. Do you have the gammacheck spreadsheet?
I would say you are losing one or more of your voltages on your t-con. This board is well marked for voltages so should be easy to check while picture good and after picture goes bad.

[Dannyx]

Re: Samsung LE23R32B picture fading to white very slowly

If gamma problem post your vgm voltages 1-10. Do you have the gammacheck spreadsheet?

I know the sheet you're talking about, it's in that thread about general repair tips I believe, but no, I don't have it right now. Should I measure the voltages with respect to chassis GND or to that REF test point on the far right (can't see it too well) ? I believe I should take a reading after a cold start when the picture displays properly and then after it messes up as well.

[dskall]

Re: Samsung LE23R32B picture fading to white very slowly

Chassis ground. Here's spreadsheet

[Dannyx]

Re: Samsung LE23R32B picture fading to white very slowly

I tried that today and with the right buffer disconnected the picture is ok - albeit washed out immediately after turning on the set, it IS there. When I connect just the right buffer however, there is no picture at all - it's just a mess like you see in the picture, so perhaps the right buffer is indeed defective. Trying to keep the board cool didn't make much difference either, because the problem still appeared even with a small PC fan over the board. The large chip is only reasonably hot - I can hold my finger on it and it definitely doesn't feel like enough heat to cause any issues. The gamma IC is hotter though. I'll try taking some measurements as well.

[Dannyx]

Re: Samsung LE23R32B picture fading to white very slowly

This is what my numbers look like immediately after a cold start. After the TV's been running for a while and it starts going gray, Voltages 10 to 7 increase by a bit - the higher the number of the test point, the higher the increase is, for instance V10 goes from 1.42 to 2.34, V9 goes from 1.73 to 2.52...the metal housing that contains the lamps also seems to get very hot and since the T-con is attached to it, it's like it's suffering from "thermal runaway" so what I did now was lift the board off the chassis entirely and prop it with some plastic trays from my parts bin to see how this goes....I don't think it will get very far though.

[dskall]

Re: Samsung LE23R32B picture fading to white very slowly

Vg voltages progress from low to high/ high to low. Either way they should increase or decrease in an even manor. Though I think you have more than gamma problems