Samsung LN52A750R1FXZA Turning on and off

[powerblackout]

I have a LN52A750R1FXZA that turns on, the backlight turns on, I hear the little startup chimes, then the TV switches off. This loops indefinitely.

Here is a video demonstrating the issue and what happens when I disconnect the main board from the PSU.

https://youtu.be/0Z0mq7BCWU0

td;dw unplugging any combination the cables make the TV not react at all when power is supplied.

I tried removing the transistors from the board to check to see if all of them are working. With my DMM I tested that they were.

None of the capacitors on the board show any signs of bulging.

When I re-installed the transistors I realized the leads were a bit dusty. I used some deox-it on them, but when I plugged the TV back in the Q1815 transistor started sparking! I quickly unplugged the TV. I reflowed the solder points and made sure there were accidental no solder bridges. There are burn mark between the middle leg and the two outer legs. I tried it once again, it sparked again, and one of the fuses on the PSU popped.

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

https://www.youtube.com/watch?v=n54IurMvr6o good video on testing power supply, is usually where I start testing with those conditions.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

Ah ok I should have jumped the wires to make it turn on without the main board connected. Just unplugging wouldn't have done anything.

Any reason why the transistor sparked on me? I don't want to just buy another one to have it also fail.

I took an air compressor to the board and got every bit of dust and deox-it. I double checked my solder points for the transistors too.

The spark happened UNDER the board, I could see the light through the PCB. It was directly under the transistor.

Here's a picture https://i.imgur.com/nqdhWHG.jpg

This happened AFTER I removed and reinstalled the transistor. I tested the transistor after and it is no longer working.

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Not sure, you think you may have put that transistor in backwards?

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

https://www.youtube.com/watch?v=4v8DcqCNG4A video on testing powersupply, I meant to post this first.

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Ah ok I should have jumped the wires to make it turn on without the main board connected. Just unplugging wouldn't have done anything.

Any reason why the transistor sparked on me? I don't want to just buy another one to have it also fail.

I took an air compressor to the board and got every bit of dust and deox-it. I double checked my solder points for the transistors too.

The spark happened UNDER the board, I could see the light through the PCB. It was directly under the transistor.

Here's a picture https://i.imgur.com/nqdhWHG.jpg

This happened AFTER I removed and reinstalled the transistor. I tested the transistor after and it is no longer working.

Some tvs the backlights will come on by just unplgging the mainboard from the powersupply board, others need to be jumpered.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

Thanks for your help!

I found a used board on ebay for $15. I'll try swapping them out and see if that fixes it.

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Thanks for your help!

I found a used board on ebay for $15. I'll try swapping them out and see if that fixes it.

I think thats a good plan, if it don't work, can always try more testing, can do more testing while you wait for the board too, up yo you.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

Can I do any testing with the fuse blown and both transistors near it shot?

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Can I do any testing with the fuse blown and both transistors near it shot?

Would be tougher, probably need a schematic and start checking right from where the power first comes into the board and trace it out from there, checking everything.

[budm]

Re: Samsung LN52A750R1FXZA Turning on and off

https://www.cnet.com/forums/discussi...itself-320011/
Once you get power supply running again.

To fix power supply board I will need good clear pictures of the whole top and bottom side of the board and closed up of the location where you see the sparks.
Power board P/N BN44-???????
If you can upload the pictures here will be best.

[freakaftr8]

Re: Samsung LN52A750R1FXZA Turning on and off

Try disconnecting the LVDS cable from the tcon board in in power back up.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

https://www.cnet.com/forums/discussi...itself-320011/
Once you get power supply running again.

To fix power supply board I will need good clear pictures of the whole top and bottom side of the board and closed up of the location where you see the sparks.
Power board P/N BN44-???????
If you can upload the pictures here will be best.

I can't get the screen to display anything, I don't think I'd be able to supply a firmware update through the system.

I have attached a back and front and a zoomed in section on the spark area. I removed the transistors already. Now that it's the 4th time I've removed it (after the initial sparking) I've torn a trace off lol.

Power board is BN4400201A

[budm]

Re: Samsung LN52A750R1FXZA Turning on and off

That section is the Inverter section.
http://www.shopjimmy.com/catalogsear...?q=BN44-00201A
You can try fixing the power supply board or buy a replacement.
I do not know how bad the damages are but here is the schematic:

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

Ok got the replacement power supply installed. I noticed this power supply had puffed up capacitors, which I replaced with good looking ones from the old board. Same issue though!

[freakaftr8]

Re: Samsung LN52A750R1FXZA Turning on and off

So did you try disconnecting the LVDS cables from the tcon board like I mentioned earlier?

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Ok, make sure you plugged in all connectors when you tried it, easy to forget one, then if no backlights, unplug tv, unplug connector from powersupply to mainboard, turn it on and see if you have backlights.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

Same symptoms when I disconnect the white ribbon that runs between the main board and the tcon board.

[powerblackout]

Re: Samsung LN52A750R1FXZA Turning on and off

I hear the chimes, backlight comes on, sits for 10 or so seconds, then the power clicks off. Continuously cycles.

[nomoresonys]

Re: Samsung LN52A750R1FXZA Turning on and off

Ok you already tried it, so I guess just leave everything plugged in and check for expected voltages on new powersupply, looking for blu on about 3 v or so but they all need to be there and correct for proper operation of course.