Samsung LNT4061FX LCD - Black Screen?

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

They use two main AC fuses (one for the Line and one for the Neutral) due to the fact that this board may be used in EURO Countries which the HOT and Neutral can be reversed.
I would check the bridge rectifier before putting in another fuse or you can use 75~100w in place of the fuse to see if the lamp will stay on bright without dimming down after few seconds, which will indicate shorted circuits exist.
I made this when i do my repair works.
https://www.badcaps.net/forum/showpo...&postcount=112

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

Bud,

Would I need to test this rectifier out of circuit, as show in this video?
https://www.youtube.com/watch?v=i4jTHhXuKLA

Also, I'd like to know what kind of iron he has there. I'm not sure mine can desolder that quickly or easily.

Thinking about working on this just for learning. I bought this set for $20, against my better judgement, because lately I've been mostly just buying cracked screens or stuff I think I can handle.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

You can test the bridge using OHM MODE (without removing it from the board for now) since we are looking for damaged diodes that are shorted out and has low Ohm. Check the resistance between the two inner pins, then the resistance between the two outer pins, report the readings.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud,

on the two outer pins of the bridge i have about 6 megaohm. Inside two pins, about 400K ohms

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud? anyone? thanks

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

It's been awhile, I will have to read the whole thread again later on to see where we were at.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

OK, remove the fuses FM801, FM802. In stall the two Main AC fuses FS801, FS802, apply the power, the FS801 and FS802 should not blow.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud,

sorry about the delay in response again. I got sidetracked with other sets, and had to get my new soldering iron going (still just the weller, but hotter and new tip). I should be able to work faster now.

Removed those two fuses which were soldered into the board. I think the same fuse is blowing FS802, while FS801 is not blowing. This is with the TCON completely disconnected. At first , I couldn't remember if the old fuse FS802 was already blown. So, I replaced it with a clear body fuse. Big flash/burn.

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

paging budm

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

So fuse FM801, FM802 are not installed, right? Just the two main fuses.
https://www.badcaps.net/forum/showpo...6&postcount=27

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

bud,

thanks for the reply. yes, i desoldered and removed FM801 and FM802. I may have burned the PCB a bit around those, but I think the traces are still intact. FS802 keeps blowing , while FS801 stays OK. Now, I did use a glass fuse, and I think that might be a fast blowing fuse. Not sure if that makes a difference.

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

OK, remove the PFC MOSFETs QP01S, QP802S.
Check the resistance of the cap CP813, CP814.
Did you make any kind of fixture to put a lamp in place of the fuse so you will not keep blowing up the new fuse?

[tucocaps]

Re: Samsung LNT4061FX LCD - Black Screen?

i haven't made the lightbulb tester, but it looks like I'll need to do this. I'm a bit confused on the simplest way to make. How do the connections to the circuit from the bulb work? I see your pictures of the box, and the bulb, and switches, but not how it connects to everything in use.

Can I just connect wires with alligator clips to each side of the fuse, and then to the light bulb socket?

[budm]

Re: Samsung LNT4061FX LCD - Black Screen?

"Can I just connect wires with alligator clips to each side of the fuse, and then to the light bulb socket?" Yes, just make sure yo use good alligator clips that will stay on and not coming off easily which can cause lots of damages if it makes contact with other circuit.