Samsung LNT4061FX LCD - Black Screen?

[tucocaps]

Hey Everyone,

I picked up this set a few weeks ago. I think it will be another parts salvage, but I'm wondering if I can troubleshoot.

When I picked up the set, I think the screen was just white when the set was turned on (or flashing white). Upon testing again, I notice I can see the backlight through holes in the back of the panel, but the screen is black.

The set does seem to function, and will play sound on playback.

Panel doesn't appear cracked, but I guess I can't say for sure. When I tap on the front of the panel, I can see the flashes of white from the backlight.

Would the TCON be suspect in this case?

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

Yes, you need to check the fuse and the voltage on both ends of the fuse on the T-CON board.
Please post pictures of the boards also.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?



Thanks Bud. Here is the T-CON. I took a look at your guide, but not sure where the fuse might be on this one? Also, what's the easiest way to test for voltage, and what range here?

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

Check FP1 (it has UC printed on top) which is next to the left of CP1 capacitor.
The DC voltage on both ends of the fuse when TV is turned on should be either 5V or 12V (BLACK probe on the chassis).
http://assets.shopjimmy.com/media/ca...bn8101870a.jpg

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

Whoah! Thanks for the fast reply Bud. Will try to check that now.

PS. That tabby on your photobucket page is a cool looking cat!

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud,

well my probes/meter aren't very good, but it looks like i got 15V on one side of the fuse, and nothing on the other.

so can that fuse be bridged temporarily, or is it fried because something else on the t-con is bad? i have a bunch of t-cons around here now, but my guess is not any that will work with this one.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

OK, it circuit after the fuse end which you do not get the DC reading may have problem that draws too much current and caused the fuse to blow, or the fuse just weakened.
But are you sure you are getting 15V which is too high, you should recheck it again.
You can also use the Ohm meter to check the resistance between that end of the fuse that does not show voltage reading and the the chassis to see if it shows really low resistance.
You can also try using 3A fuse by solder the wire to each end of the fuse and then solder the wires to each end of that blown fuse.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

hmm I might try the solder 3a auto fuse idea. i actually replaced one of these pico fuses that way in a marine computer once.

not sure on the 15volts, but my meter is really cheap and low quality. also the battery was going dead on this one i think. maybe i'll replace the battery and read again.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

I use pico fuse also in place of the SMD fuse, just have t bend the legs.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

Well, I think I may have made it worse

I couldn't see me soldering that 3 amp fuse with my limited solder skills, so I decided to try bridging the fuse.

When I powered back on, I heard what sounded like the PS clicking on/off about every second. So, I decided to lift up the set and see what the front looked like. Didn't realize I had the T-CON cover loose on the chassis. It fell and arc'd across something on the PS board. Blew my GFCI. Learning

Looked at the PS, and found a blown fuse right next to the cord input. It's a 250V canister fuse. So, I scavenged one off another board. Powered on again. This time that particular fuse didn't blow (still tests OK with Ohm meter), but I saw a small spark on the PS , and then nothing.

What I'm wondering is if bridging the fuse on the T-CON did this, or my idiot move of arc'ing out the PS with the cover from the T-CON did it. There is a small burn mark on one of the PS heatsinks, so I know I arc'd something.

Thanks for any ideas!

[vinceroger69]

Re: Samsung LNT4061FX LCD - Black Screen?

we all make mistakes part of learing i guess but now you have probably caused a lot more damage can you upload a picture of the area on the psu where you saw the spark.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

Thanks Vincer. I will upload a picture of the supply. It blew the other fuse after that second spark. It seems there are two fuses close to the power cord input. I'm reluctant to put a new fuse in there, as I think it may blow. Although I am curious as to why the same fuse didn't blow the second time.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

That heatsink on the power supply board probably is at line potential which is another reason I tell people not to touch any part of your body to the power supply board. Blowing the main AC fuse is due to the T-CON shorted circuit in the primary side of the power supply when it fell.
The clicking sound you heard before the board fell down is probably form the power supply was turning on and off due to short circuit on the T-CON board whuich was the reason for the fuse to blow in the first place.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

thanks bud. is the set able to power on with the t-con completely disconnected? the t-con for this set is kinda pricey, and i'm thinking about just salvaging parts if I can. Of course, now I'm not sure what I have, so I'll need to test more.

I'm not entirely sure I understand everything you said, but I think you are saying it's safe to assume the t-con is otherwise "fried", or was fried before I started?

Here is picture of the PSU, and the area by those fuses (first one that blew is removed). I think you can see the burn mark from the arc that happened.

[/ATTACH]

[vinceroger69]

Re: Samsung LNT4061FX LCD - Black Screen?

its probably blown the bridge rectifier as a guess, i will let budm explane how to run a test i hate trying to explane things.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

OK, it did touch the HOTSIDE HEATSINK.
At least now we know that the T-CON is bad for sure did to the blown SMD fuse.
Now we need to fix the power supply board, so here is the diagram, the bad news is that when the T-CON touched the HOT HEATSINK, the fault current flow through the Ground wires of the LVDS cables then to the chassis safety ground so there may be some damage on the main board also which is not good.
There are two fuses, one is for the MAIN AC fuse, the second one is for the backlights inverter circuit. If the one for the inverter circuits is blown, then you have even more problem.
You are going to have to check the MOSFETs in the inverter section, the bridge, the MOSFETs in the power supply section.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud,

that sounds really complicated. you think i can check all that? still trying to pull up this pdf. it has some special language pack.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

does it mean anything that the main fuse appears to have blown before the inverter circuit? in the picture I sent, the first fuse that blew was removed. Not sure which one that is.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

"does it mean anything that the main fuse appears to have blown before the inverter circuit?" I do expect the main AC fuses (two of them) closed to the AC INLET to blow when the T-CON board made contact with the heatsink.
The other two fuses are those red cylinder looking case.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

You mean the t-con cover? I think basically that piece of metal made contact. I guess I'm wondering if there would be any point to replacing that second fuse, since the other one didn't blow after I replaced it. I don't know how much the fuses cost, but I don't have any , except on boards to scavenge.