Samsung LN40C630 won't turn on

[gingerbreadman]

I have a Samsung LN40C630 LCD tv that won't turn on. I have replaced both the main board and the power supply.
There is a red light on the front the goes off when I push the power button on the remote, but after that the tv is unresponsive.
What should I do next?

[freakaftr8]

Re: Samsung LN40C630 won't turn on

Take a flashlight and look into the screen. See anything?

[budm]

Re: Samsung LN40C630 won't turn on

Pictures of the board? Power supply board P/N BNXX-XXXXX?

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

Thank you for your replies. I looked at the screen with a flashlight, I couldn't see anything.

Attached is some pictures as requested. There is a picture of the part number also.

[tom66]

Re: Samsung LN40C630 won't turn on

Schematic of power board


Across two yellow 450V capacitors, check the voltage before & after power button pressed. Expect 160V~170V in standby, 380~400V run.

Unplug T-con and check if set powers on.

Do not rule out the chance of a dud main board. Very common on these sets.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

I checked the voltages on the 2 yellow capacitors. They were right at what you said they should be. I was checking some of the voltages going out of the power supply though. I only found 3.6 volts on some of the pins, not the 5v, 12v or 13v it specifies.

Unplugging the T-con board didn't seem to do much. But one of the times the red led light wouldn't go off when I pushed the power button on the remote (meaning I don't think the set powered up) and unplugging the T-con seemed to help that. But then after that with it still plugged in it powered up. The buttons on the tv don't seem to work, the only thing that works is the remote.

[tom66]

Re: Samsung LN40C630 won't turn on

What you are saying is you did get it to rise from 160V to about 390V±15V when you press the power button?

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

The voltages went from 160v to 387v when turned on.

[tom66]

Re: Samsung LN40C630 won't turn on

OK, and the 13V doesn't appear?
That is unexpected, because the one transformer generates all the power rails, all the power board does is switch them on using QM851,852.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

I just rechecked it. On the pins that are supposed to be 13v it only reads about 3.6v.

[tom66]

Re: Samsung LN40C630 won't turn on

Can you see diode DM852 on the heatsink near the 13V, 5.3V, etc. output connector? Test the voltage on both ends with red probe, and black probe on chassis.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

I attached a photo with a red circle around the one I think you're talking about.
If that's the one I can't see how to reach it with my test probe.

[tom66]

Re: Samsung LN40C630 won't turn on

You're right. Looks difficult. You might have to solder a lead to that pin to measure it while the board is attached to the chassis.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

Do you mean to solder a lead to the under side of the board and then re-install the power supply to test it?

[tom66]

Re: Samsung LN40C630 won't turn on

Yes, probably best to do both leads at once so you can test both.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

I removed the board to solder the leads on it and found out that both DM852 and DM853 were pushed through the board and the circuit board was broken around them. So I guess I'll be looking for another power supply.

[tom66]

Re: Samsung LN40C630 won't turn on

Not necessarily. Such damage is often repairable. If you show us a picture, we may be able to judge if that is the case.

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

Okay, here is a couple pictures of the damage. Let me know if you need different pictures.
Thank you for all your help so far. I appreciate it.

[tom66]

Re: Samsung LN40C630 won't turn on

Looks quite fixable.

First of all identify why that occurred, the only reason it could have occurred is the heatsink was pushed down, but this is not normally possible due to solder tabs. Check they are all soldered in place and that none have slipped or broken.

Then, solder wire links to the respective copper areas. To get a good place to solder you will need to remove the solder mask from the board. This is what gives the board its green colour. A small blade or flatheaded screwdriver works well. Just scrape lightly on the appropriate area and you will reveal the inner copper. Once you have a bit of copper exposed, solder as indicated in the diagram.

Blue areas: expose the copper
Red areas: solder a wire

[gingerbreadman]

Re: Samsung LN40C630 won't turn on

I soldered those wires on. The tv powered on and seems to work great! Thank you so much for your help Tom66!