Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

[Jooo]

Ok, so I got this LC-Power LC6550G power supply, which does not work properly.
It turns on for 1 second, just enough for the fan to turn a little.
I tested it connected to a motherboard, and with no load at all, and with a CD drive connected to Molex connector.
Every time it just turns on for second.

The 5VSB line measures 5V all the time.
12V line measures 12V for a short time when trying to turn on, but then goes back to 0V.

The previous owner said "Even though I removed it today from use, the computer it was in often had problems cold-starting when not being used for a long time"

Here's some pictures of identical PSU
http://i.pcworld.fr/139431-lc-power.jpg
http://i.pcworld.fr/139441-lc-power.jpg
http://i.pcworld.fr/139431-lc-power.jpg

I hope some of you can help me trying to fix this power supply, I will appreciate it

[tom66]

Re: Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

I have had this issue before, it often turns out to be a bad capacitor on the output side.
Going by the general build quality, I'd put that at a low 300W maximum. No way it's 550W capable.

[Jooo]

Re: Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

All caps are atleast visibly good, they are mostly Teapo, which will do fine for my use
I'd not like to replace all the caps and then find out that it's still not working.
Can any specific cap cause this? 5vsb cap?

I know that it is not capable of doing it's rated wattage, it will explode somewhere around 400 - 430W load.

[rogfanther]

Re: Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

Have you tested the secondary diodes for shorts ?

[Wester547]

Re: Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

That looks like a Huntkey, which besides the use of half bridge topology (bipolar transistors), Chinese capacitors, the dishonest rating, and lack of OPP, actually looks like a decent build to me. FCon is a very common choice for secondary capacitors in Huntkey power supplies so if there are FCon capacitors in there it's possible they've failed, if not some other very low end brands they used to use - BH and KSC come to mind. Actually, if I'm not mistaken, I might have spotten a small, blue BH (CD288?) capacitor right next to the voltage doubler (by the passive PFC - the heat from it must have not helped - it looks like it's easy to remove as well, so if it isn't necessary for the operation of the PSU, I don't think removing it would hurt... but then your PSU might not have that near its voltage doubler as it isn't the same one as the picture). I think 300W is a good limit for it too. I'd say it would be a good PSU after it's recapped (though it could have a self-oscillating, two-transistor +5VSB circuit with feedback).

[Khron]

Re: Need help to fix a LC-Power LC6550G 550W power supply: turns on for 1 second

A shorted rectifier is a good possibility - just had that happen to me yesterday, on a 600w Solytech i was recapping. Before that, all was fine. After i finished the recap, it wouldn't stay on more than a second.

Culprit - somehow the -12v diode got shorted A UF3003. Replaced it with a UF5408 and all is fine