Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

[dicky96]

Hi guys
I have this Samsung 32" TV here UE32C6530UWXXC

It powers up, goes - back into standby - powers up..... and there are a couple of clicks coming from a relay on the PSU during the power on off cycle.

However sometimes it will power up and stay powered up - it does this maybe once in every 10-20 times i try it.

When it is powered up I have lines down the whole screen - it looks like a TCON or LVDS problem. However reseating the TCON and LVDS cables doesn't help to improve matters

I get the same problem on either side of the screen with just one TCON cable connected

When the set will stay powered up I have a window slowly moving around the screen saying 'Check Signal Cable' which is to be expected as I have no video source connected. The areas of the screen where this has moved from turn black, no lines in these part of the screen once the window has moved.

I initially thought I have a PSU problem, but the 12V, Audio Power and 5.4V lines are present all the time, even when the set is cycling into standby, it's just the backlight LEDs going off. All the caps on the PSU look OK.

However this also looks like a TCON problem.

I made a short video here https://youtu.be/UtxZbolvlCY as it is easier to show the problem than describe it.

Pics also attached

Rich

[diif]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

C series image issues I look at the BGA on the main board.

[dicky96]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

Thanks diif

There are three large BGA on the main board which have hard rubber foam type pads on them. I pushed down on all of them firmly with my finger then powered up and got a good picture. However when I tried to stand the set up the fault came back.

Applying pressure while the set on it seems the problem is more likely on the BGA nearest the top of the set although it is so sensitive I can also clear the fault pushing down firmly on the largest one in the middle.

Holding down on the one nearest the top with moderate presure does seem to give a stable picture. I have a hot air station but couldn't work on a BGA this size.

Maybe applying some sort of shim between the back panel and the BGA to maintian pressure on it would get it working but I am not sure how reliable it would be

Has anyone tried this technique on a BGA?

Cheers
Rich

[tom66]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

Maybe applying some sort of shim between the back panel and the BGA to maintian pressure on it would get it working but I am not sure how reliable it would be

Has anyone tried this technique on a BGA?

Cheers
Rich

It wouldn't be reliable. It would be like trying to hold together your mum's best china with a vice grip. The solder joint is cracked; you need to reflow it.

[dicky96]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

OK. I have a hot air rework station and can give it a go. I've tried this on MAG 250 iptv boxes with some success.

What is the grey pad stuck to the top of the BGA chip? Would that melt and and does that have to come off first?

I thought it was some sort of rubbery plastic thing but it is hard and rigid.

[diif]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

It doesn't melt, I think it's some sort of ceramic, grab with pliers and twist off.
It needs to be removed as it will do it's job and absorb the rework heat.

[dick_barton]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

I believe that if you are going to reflow the BGA IC it is better to heat the underside of the board to around 120 degrees, low enough for components not to fall off but hot enough so that when you heat from above it will not warp the circuit board. Use thermocouples to measure the temperature top and bottom so as not to overheat the IC.

I've never been successful but others may offer you their method.

[dicky96]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

Yeah the ceramic grey thing came off with a bit of waggling. The BGA still worked with same fault as before i removed it.

Unfortunately I don't have a preheater plate - but I do have an electric oven I can set to give bottom heat only

I just tried without preheater or oven first. I only have a WEP 858D rework station which isn't the most powerful of things and I took my time gradually warming that area of the board before concentrating the hot air directly at the target and I struggled to get the top of the BGA above 210C measuring with an infra red laser thermometer. So that wouldn't be quite hot enough.

I will let it all cool down and see if it is still working. I could then try warming the board in the oven to 120C and see if I can get the BGA hotter, nothing much to lose here I guess. I did explain to the owner the cause of the fault and the possibly destructive result of trying to reflow it given the equipment I have available

*update*. It powered up and worked fine for about 15 seconds - then the fault came back same as before. Applying pressure to the bottom corner of the BGA gives a clear pic.

[tom66]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

The ceramic grey thing is a heatsink for the CPU, an inadequate one at that, but that's Samsung value engineering for you.

[dicky96]

Re: Samnsung UE32C6530UWXXC lines down screen and standby cycling. PSU or tcon fault?

An update on this one:

I tried setting my oven to 120C and warming the board up for 10 mins. I then gave the dodgy BGA a good warming with my hot air station but still struggled to get the temperature above 220C according to my laser IR thermometer.

After cooling the board was tested but now I have a blank screen. So I guess I wasn't very successful with trying to reflow a BGA either.

Rich