Last night I put together my first build. It was quite an interesting experience, time consuming but worth it. I haven't got to around to actually hooking up the cables though. The scariest part was pulling down the CPU lever.
So anyway as the subject says I'm confused about the PSU installation.
My case is an Antec 300 and the PSU is a Corsair 650HX. It looks like this:
I have always seen them mounted with the fan facing up when it is a bottom mount case unless the case has vent holes in the bottom under the power supply to suck in fresh air. I have the antec 902 and it is also a bottom mount and had this very same question when I got to putting everything together. Almost 100% of the responses I got told me to mount it with the fan facing up unless there are vent holes underneith the power supply. Piece of advice when your building and you have the fan facing up: cover it with something in case you drop a screw so it doesn't fall in the power supply. Not exactly sure why your holes aren't matching up though...
With a bottom mounted PSU you have the two options that you described above. On modern PSUs the large fan on the bottom is an intake fan to bring cool air into the PSU and the smaller fan at the rear is an exhaust fan to expel the hot air.
If you have the PSU mounted fan-side down then it can draw cool air in from outside of the case and help keep the PSU cool. This approach makes more sense to me personally, however the Antec 300 (I also have this case) does not come with a fan hole at the bottom of the case for this approach. I plan to mod my case and install a 120mm fan hole, grill & dust filter and also install some higher profile feet so there is more clearance for air to be drawn into the case. The dust filter is important since dust will settle on the surface of wherever your system is sitting and you don't want this in your PSU. Also, common sense will tell you not to sit your system on carpet if you choose this method.
The alternative is to have the fan facing upwards which has the effect of drawing hot air out of the case which may help cool other components in your system.
If it were me I'd mount it fan side up for now simply because you aren't going to drawing cool air into your PSU with no fan hole in your case - you're more likely to just pick up dust from the inside of your case that has settled on the bottom. It's up to you to decide however, whichever suits your needs best.
Although, are you 100% certain that you can only use two of the screws? You should be able to hit all four of them with a standard ATX PSU - I know I did with my Antec 300 case. Four is a lot more secure than two and the last thing you want is a PSU that's on the wobble under load.
I kept it in the face up position since the case does not have any holes in the bottom as you guys said. I didn't know such cases existed but it's fine.
Regarding the screws, the top two are perfectly aligned with the holes, but the bottom two don't have any holes. I put in two screws anyway, the screw head slightly touches the chassis so I guess it's better than nothing.
Last night into the early morning I continued with the build, particularly the cabling. Boy, that was an UNPLEASANT experience. The cables are so hard to maneuver inside the case, I especially had an issue with the EATX12V plug.
It was positioned at the back of the case behind the HSF. I guess I should have bought a smaller HSF since it took me like an hour for just that plug but I guess live and learn. And the front panel audio wire BARELY made it. You would think the motherboard would logically have that on the front of the board, but no.
It doesn't look very pretty but I grouped them with those whatchamacallit locking strings and nothing is near the fans. I also taped the back/top Tricool switch to the case.
I didn't have time or energy to actually hook it up to a monitor yet (I'll do that today or tomorrow), but I powered it up. The board lit up in several places as it booted and then the lights disappeared. According to the manual the test is good so I suppose I'm OK. All the fans work and no apparent problems. I was actually pretty impressed by the noise level, you can barely hear it with all the fans.
One thing that bugged me though is that there is no POST beeps. For a while I thought I messed something up until I did a google search and found that this case doesn't come with a speaker to make a noise. I guess that's what the board lights are for. I've been used to beeps for the past 20 years just seemed odd.
Anyway, just thought I'd post this in case it helps anyone.
I was probably the slowest computer builder.
Next step is the OS and should be set.
By the way, does anyone know if I can monitor the GPU fans? It's a Gigabyte Nvidia GTX 460, it has two small fans on it. It kinda looks cheap, would be nice to check if they're functioning without having to open the case up every week or so.
Oh and speaking about the GPU, when I put in the PCI-e power connector, it was a 4+4 pin but there was also a 2 pin hanging off of it. I couldn't find any place to connect that and the manual doesn't mention it, so I guess that's OK?
Thanks again guys, Toms Hardware was a great resource.