Samsung TV Power Board bn44-00440b

[Bluekazoo]

Trying to repair this bn44-00440b board for my Samsung TV.
The TV was in use when it died, just clicked off.
No indication of power at all.
I found that the fuse at FS801S had blown.
The fuse was replaced, and immediately blew when the TV was turned back on.

It was suggested that there was a short to ground somewhere on the board.
Using the continuity mode on my multi meter I tested from a grounding screw to many points on the board.
I did not find a short.
I could not find a schematic for this board, and looking at other posts on here no one else has either.
Since I'm really using this repair to learn more about PCB repair I decided to bypass the fuse.
The MOSFET at QP802 did not survive that experiment.
I removed that component, and checked for a short to ground, again I can't find one.
Just looking for some advice.
I would just replace the MOSFET, and try again, but I'm concerned I'd just end up cooking something else.

[neilc6]

Re: Samsung TV Power Board bn44-00440b

If the fuse is blowing, you should be able to measure a short (may be very low resistance) on the other side of the fuse to ground. You can use hot ground as well which is the negative side of the big caps. You may be able to measure a short on that FET. There should be some videos on youtube on testing FETs. Again low resistance would indicate it is shorted and failed. It doesn't have to be zero ohms. Dust between high voltage pins can also ignite which is why some boards fill the space with silicone or glue.

[nomoresonys]

Re: Samsung TV Power Board bn44-00440b

Need to clean that dust off if you haven't already, dust is a major killer of electronics.

[Bluekazoo]

Re: Samsung TV Power Board bn44-00440b

The FET did fail, it's the component in one of the pictures. Nice little hole in it.
The dust did end up getting cleaned off a while ago.

[yokoono]

Re: Samsung TV Power Board bn44-00440b

I advise you to call an electronics technician for repair. You have too little knowledge to repair. There are too many burned components related to PWM and PFC circuits. In addition, the working voltage is very dangerous (400V).

[Bluekazoo]

Re: Samsung TV Power Board bn44-00440b

Thank you for your concern yokoono, I am aware of the voltage involved. It is printed clearly on the caps and board.

[yokoono]

Re: Samsung TV Power Board bn44-00440b

A real electronics technician, if he has found the burnt fuse, does not replace it and checks if it has been fixed. A real electronics technician checks WHY HE BURNED. Possibly you have burns: rectifier bridge, mosfet, integrated controller, resistors, diodes, optocoupler, possible mosfet, controller on the PFC circuit and related components, etc.

[nomoresonys]

Re: Samsung TV Power Board bn44-00440b

Repair kit there, you never know if they have all the parts you need to fix it but it also gives you a good idea of what parts to check: https://www.ebay.com/itm/Samsung-BN4...UAAOSwvNpegzQ~

[nomoresonys]

Re: Samsung TV Power Board bn44-00440b

Maybe build a simple dim bulb tester to keep from blowing up your parts and fuses, one of many threads there and youtube is loaded with how to vids: https://www.badcaps.net/forum/showth...voltage+tester

[nomoresonys]

Re: Samsung TV Power Board bn44-00440b

There's a whole powerboard there, 33 bux, don't know anything about them never used the site, says wholesale so I don't even know if they sell to the public: https://www.abctay.com/wholesale-sam...ute-p-843.html

[nomoresonys]

Re: Samsung TV Power Board bn44-00440b

There's a board on ebay for like 57 bux all toll but seems a bit high for a 40 inch tv powerboard.

[budm]

Re: Samsung TV Power Board bn44-00440b

"Using the continuity mode on my multi meter I tested from a grounding screw to many points on the board.
I did not find a short."
Just for learning and FYI when testing testing the circuits.
The cold side circuit ground is usually connected to the ground screws/board mounting screw.
The Hot side circuit ground is not connected to chassis, the ground ref for hot side circuit will be the negative leg of the main filter cap.
BTW, using continuity mode, most meter will beep when testing continuity up to 100 Ohms, which does not mean dead short circuit, need to look at the Ohm reading too.

[thommyX]

Re: Samsung TV Power Board bn44-00440b

https://www.ebay.com/itm/SAMSUNG-LN4...-/163042099229

hope it helps.

LG Thomas