Samsung LE40A656A1 total power loss. Help!

[madmatt]

Hi guys, I have the above model tv that I was watching quite happily, when suddenly it turned off. Complete power failure. No light, nothing. I have checked the plug fuse, even tried a different power cable still nothing. I have had the back off and looked at the boards, and there is no obvious defects. All caps look good.
Any ideas? Googling the problem only seems to show the common clicking fault, but this doesn't get that far.
Heeelp???

Look forward to your replies!

Regards

Matt

[sordids999]

Re: Samsung LE40A656A1 total power loss. Help!

https://www.badcaps.net/forum/showthread.php?t=39740

This may help you

[Alastair E]

Re: Samsung LE40A656A1 total power loss. Help!

This is one of the models with that rubbish yellow-glue that carbonises on the PSU isnt it....?

Check for that yellow glue on the PSU and where its found--remove it, also check for burns in/on it too....

That glue is a construction-adhesive, was Never intended for the use TV makers have put it to! Its been around for 30 years or more--and has caused problems All that time!

[madmatt]

Re: Samsung LE40A656A1 total power loss. Help!

Ok, thanks for your replies. Here is a photo of the psu board. The glue doesn't look burnt at all. I haven't checked the fuses on this board yet but am about to(sorry!)
Thought all faults on these very common tv would be well known? Suprisingly can't find an answer to this one!

[madmatt]

Re: Samsung LE40A656A1 total power loss. Help!

Ok, there is a white fuse, T6.3AH250V that seems to have blown!

[madmatt]

Re: Samsung LE40A656A1 total power loss. Help!

Ok, there is a white fuse, T6.3AH250V that seems to have blown!

Does anyone know what would have made this fuse blow?

[budm]

Re: Samsung LE40A656A1 total power loss. Help!

Shorted rectifiers, shorted MOSFETs, shorted ICs, etc.
See SCH PDF.

[madmatt]

Re: Samsung LE40A656A1 total power loss. Help!

Shorted rectifiers, shorted MOSFETs, shorted ICs, etc.
See SCH PDF.

Wow, and ouch! Where do I start? Am getting a couple of fuses today so will replace and try but I guess it will immediately blow. (Hopefully not!)
If it does can you explain where to stick my meter probes(I've only replaced caps in the past and inverter boards for repairs!)

Many thanks for the replies, I really do appreciate it. Be thrilled if I can repair it!

Matt

[Dang]

Re: Samsung LE40A656A1 total power loss. Help!

I personally would be looking for anything obvious after the fuse and checking all components near or along any circuit path related to, if nothing shows up check all other components, those fuses will likely go again so before wasting a pound or so, get the DMM out and check for shorts etc, you'll find your issue in the end, just persevere, Andy.

[tom66]

Re: Samsung LE40A656A1 total power loss. Help!

Worth trying a light-bulb tester across the fuse. Easy enough to build, just need some wire, croc clips, a lamp holder & 100W bulb.

[Ltank]

Re: Samsung LE40A656A1 total power loss. Help!

Replace FS801. Check QP801 Mosfet and QP802 NPN Transistor for short. Also check
DP801 High Speed Switching Diode for short or open. You may need to rmove them from cirduit or remove solder from one leg to test.

[madmatt]

Re: Samsung LE40A656A1 total power loss. Help!

Thanks for the info.
Replaced the blown fuse(bought 2) and as expected, bang!
Will
Follow ltanks suggestion above now. (If I can find these so-called mosfets, as I'm a complete newbie but enjoying the learning experience) as stated above Capacitors and inverter boards are my only repair experience to date(both fixed and still working fine!)

[Ltank]

Re: Samsung LE40A656A1 total power loss. Help!

Mosfets and transistors are attached to heat sinks so they are easy to find. Alot of times you will see a Q number for both mosfets and transistors. Diodes will have a D number and Zener Diodes will have a ZD number, Zener Diodes dont check same as standard or high speed switching diodes (not interchangeable).Look online to learn how to check these parts with a DVM. It takes a littke effort but after while it becomes second nature.