Botched SFX PSU fan swap

geckokarma · Post by **geckokarma** » Sun Apr 02, 2006 9:38 am

Drat! You know that trade off between prudence and expedience? I have come out on the wrong end this time!

I just picked up a Seasonic SS-250SVP. Naturally, with the stock fan, it was still too loud. So I went for the fan swap. Here's a photo of the guts of the Seasonic.

Note that the fan header is mounted on a vertical board, and so the pins make a 90 deg bend. And its not pressure fitted; its glued. That's different than most of the ATX PSUs I see posted on SPCR.

I figured well, as long as I was more or less gentle in removing the header, I should be fine. But no such luck! I carefully pried the header off the board, but the pins came with it! After muttering under my breath, I removed the pins from the header and put them back in the board. They were as loose as could be. Does not bode well.

Figuring the damage was done and what did I have to lose, I decided to go ahead and plug in the fan, close the box, plug eveything in and fire up the PC. Good news: the mobo power LED came on when I flipped the PSU switch. Bad news: when I hit the PC/mobo power button, as I recall the PSU fan kicked on for a split second, then nothing. No activity from the PC.

Maybe its b/c the fan pins have little/no contact. Or maybe I inadvertantly broke something else in the PSU (but I don't think so).

What's going on? Does the PSU circuitry detect that the fan is dead or its circuit is open, and therefore refuse to fully power the PC?

I'd also appreciate opinions on:

Is the PSU probably toast and I'm better off buying another?
If not, should soldering the pins to the board fix it?

Thanks in advance!

IsaacKuo · Post by **IsaacKuo** » Sun Apr 02, 2006 10:23 am

I don't know about PSU's in general, but the PSU's I've used so far don't mind if the fan is disconnected. I prefer running fans at a constant 5v, so I simply rip out any existing connections to a 12v or temperature controlled fan and rig up a 5v connection to one of the molex connectors (from outside the PSU).

Maybe something loose caused a short circuit which killed the PSU or caused it to go into a safety shutdown. I'd try removing the fan and those broken headers entirely, and see if the (fanless) PSU can power up the PC at all. If so, then either consider the benefits of running fans at constant speed or sell that PSU to me.

The main advantage to running fans at constant speed is that it reduces the perceived noise level compared to variable speed fans. A constant flat noise blends into the background, whereas even a very quiet noise which changes (ramps up/down) is noticeable.

m0002a · Post by **m0002a** » Sun Apr 02, 2006 11:29 am

I would not be surprised if the reason the PSU will not boot up is that the fan is not connected. I would definitely try to solder the fan wires.

A few years ago I replaced the fan on a SFX PSU, but I cut the fan leads half way and soldered the new fan wires to the old leads, then covered the solder joints with electrical tape to provide insulation.

geckokarma · Post by **geckokarma** » Tue Apr 04, 2006 6:00 pm

Thanks for the tips.

IsaacKuo, you had it right. I removed the pins and got it to boot.

I'm tempted to run it at 5V... Still I'd like to get those pins soldered so I at least have the option of letting the PSU ramp it up (e.g. in summer)...

m0002a, I like your wire splicing but when I did my hack job I did not yet have (or want) a soldering iron. However, now that I have one I feel I've passed a rite of initiation...

jhhoffma · Post by **jhhoffma** » Tue Apr 04, 2006 7:22 pm

A soldering iron is like the knight sword of geeks today. It gives one a sense of power and determination and the overwhelming urge to go right the wrongs of the world.

...Or fix whatever you just messed up.

geckokarma · Post by **geckokarma** » Mon Apr 10, 2006 2:34 am

This just in: more stink.

I soldered the tips of those pins to the back of the board, leaving some respectable-looking cones of solder. Neither of them touch any other metal as far as I can see. Feeling confident, I hooked everything up, powered on, the fan spun for ~1 sec, but then died: no boot. I then tested with (1) no fan at all and (2) the stock fan: same result.

Clearly the PSU is recognizing all is not well... Does the set of possibilities consist only of a short circuit and an open circuit? Certainly, "no fan" is not a showstopping open circuit, since that did work previously (earlier post). I'm discouraged that running without a fan worked before my soldering, but not after.

Looking at my solder job, it seems more likely it could be an open circuit than a shorted one, but clearly this is counter to the evidence.

Any clues? References on helpful PSU circuitry details?

At this point, my next step would likely be to remove the pins again and try running without a fan (then, if success, power a fan as IsaacKuo suggests).

IsaacKuo · Post by **IsaacKuo** » Mon Apr 10, 2006 4:13 am

You soldered it to the back of the board? Do you mean the side which is up against the side of the PSU's case?

Then I'll bet the short circuit is being caused by the same thing that caused your first short circuit--contact with the PSU case. The PSU case is connected to ground, so anything with voltage that accidentally touches the PSU case will cause a short circuit. Whether that's header pins that are poked too far in or respectable-looking cones of solder...

[edit added:]

This reminds me of one computer where I couldn't get it to power up and couldn't figure out why. It didn't have any case, so I was just testing out how compact I could get the components. I simply rested the motherboard on top of the PSU. No boot! No boot! What the heck? I knew the PSU was good. I knew the mobo was good. Huh? I kept on trying to power it on. Nothing! No boot again! Huh?

Then it hit me. The back of the motherboard? It has more than a few pin tips poking through. What is the probability of a short circuit when I'm resting the motherboard on top of the PSU? Hmm...

Luckily, I didn't cause any damage.

geckokarma · Post by **geckokarma** » Mon Apr 10, 2006 4:45 am

Good thought, IsaacKuo. But its the back of a tiny vertical "riser" board (barely visible in the photo link in the OP). Parallel to the back of that riser is a thin sheet of plastic, I'm sure included as insulation against the board touching the rail.

I did consider which side to solder to -- the back (green) or the front (tan). I've always assumed that the metal that the pins ought to be making contact with is hidden inside the board, but maybe this is naïve. If that is the case, then it could well be tricky to get the solder to touch it. However, as I mentioned earlier, it seems my problem at the moment is not an open circuit. I suppose another possibility is that the pins need to connect to a tiny wire on the board itself, presumably visible ... but anything is hard to see on that little thing wedged in as it is. I admit I'm clueless on PCBs!

The back of the riser has a few other other solder points (e.g. for one of these) but the front has none, so it sure seemed like I chose the right side.

IsaacKuo · Post by **IsaacKuo** » Mon Apr 10, 2006 5:04 am

Well, you've got me. I rarely play around with solder, myself.