Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

[socketa]

This was in a case that had being stored for a while.
It didn't appear have enough power to spin the CPU fan. (although the CPU fan spun up when i plugged in another PSU and also when i plugged the original PSU back in)
But i noticed that the PSU fan wasn't spinning,
So i checked all of the rail voltages, and they were in spec.
Took it out of the case, and all was good, except for the PSU fan not spinning
Heating the thermistor, that's on the secondary heatsink, with a hair dryer, didn't activate the PSU fan.
Plugged PSU back into the motherboard, turned it on, and then it shut down after several minutes (PSU got too hot?).
Now the 5VSB is 6.1V

It's got a TOP222 chip, so i searched for that, and found this:

I worked on one psu that had a TOP222. They have an aluminum cap going to the control pin - for frequency or timing. The cap had gone HI ESR, but the 5vsb simply stopped and went to zero. Somewhat of a "critical" cap but does not go overvoltage when failing.

So, it looks like the chip is probably OK (i checked the cap anyway, and it tested good)
I also checked the standby ouput cap, it has good ESR and capacitance. Tried another capacitor, just in case, but standby is still a steady 6.2V.

I was going to test the TO-92 transistor to see if that was what was causing the fan to not spin, but now have to get the standby running propely first.

Any thoughts as to where to check next?

[socketa]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

on the other side of the heatsink was the other capacitor
LXJ 10V 680uf - measured 760uf and 0.2 ohms ESR - No bulging at the vent
i'll recheck the standby , and update

[socketa]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

Looking at the datasheet, and considering the temperature, that cap looks ok enough.
I tried a couple of lower ESR caps, and they just pushed the voltage up another 0.1V
Noticed that there is 110 oms to ground, and thought that that was a bit low for minimum load
So looked a bit more, and noticed this on the daugther board.
I guess that they didn't switch glue colour, and the the brown 'glue' is the contents of the leaked capacitor.
It's not vey conductive ~ 20Mohms
Will update after cleaning it up

[Per Hansson]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

Well, take note that this chip is not a fixed 5v regulator.
So any failure in the feedback path (they call it "control" in the datasheet) could make the 5VSB higher or lower, depending on what component failed...

[CapLeaker]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

The top222 is just a 3 pin device. Source, drain and control. You got to look at the whole control circuitry on both (hot and cold) sides. There is an example on the spec sheet.

[PeteS in CA]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

Is there a 3-terminal regulator in the secondary circuit for the 5VSB? E.G. a 7805 or an LM317?

[socketa]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

Is there a 3-terminal regulator in the secondary circuit for the 5VSB? E.G. a 7805 or an LM317?

Not that i can see.
I replaced the leaked cap, but still no improvement,
so took the daughterboard off, and noticed another crispy brown blob on the TSM111CN supervisor chip and adjacent area, and it had eaten away at the PCB coating.
Seems like a portion of the contents of the leaking cap, dripped sideways (or the case changed orientation duing the leaking), landing on to the top of chip, and then on to the PCB around the chip's pins
So maybe the leaked electrolyte was creating some capacitance?
I tried to unsolder the chip with an iron so that i could check if there was any more damage to the PCB; but and got frustrated with it, so cut it off and have ordered another one - which wasn't a paticularly good idea because there was no damage, so the chip didn't need to be removed.
Will update when it's back together
I removed a 100ohm, minimum load resistor, so as to clean up the electrolyle

[socketa]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

Yep, it was the supervisor chip
Replaced it, and now all voltages are good...
The fan runs for a couple of seconds if the NTC switch isn't hot enough (actually it never gets hot enough)
The The fan wont come back on when running when using a hair dryer on the NTC 'switch'
Maybe one of the transistors is on it's way out?
so i paralleled the NTC it with a 2k pot, and ajdusted it to the point where the fan just comes on
It's a real tight range, on the pot, where the fan will run lower than 13V or not at all.
and sometimes when i get it to run lower than 13V, the fan wont come back on (without adjusting the pot) after i switch off the PSU

Why's one side of the fan connected to -5v
Shouldn't the fan be connected between 12v and ground?
i don't think that 12v rated fans should be running at 13v

[stj]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

bypass all that shit and let the fan run as it's makers intended

[socketa]

Re: Liteon PS-6251-2H8 - Top222 - 5VSB >> 6.2V!

na, i like the reving sound, and it can save me 2 cents a day if the fan's not running when it's cold
got it working anyway - the trim pot that i was using was faulty (probably due to me overheating it)