Aja on 11/9/2008 at 06:36

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Actually it does more than just that -- after I shut down the computer, two unwanted things happen: a strange loud pulsing noise emanates from the speakers, fading in after a minute or so and staying indefinitely, and the case and CPU fans all twist slightly in time to the pulse (it's a little ballet!). For the past few months I've been hitting the I/O switch after shutdown, getting pretty sick of that. Any ideas?


Not sure if it'll help, but here's the specs:

AMD Athlon XP 2800+
Asus A7N8XE Deluxe motherboard
Radeon 9800 Pro graphics
Antec SmartPower 400 Watts

I already tried disassembling everything and cleaning the contact points; no luck.

baeuchlein on 11/9/2008 at 22:10

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As Bikerdude already told you, it is verly likely that this Power Supply unit is defective and about to fail. What you see and hear appears to be caused by the PSU. It is allowing variable electric currents to enter your computer and power up the fans as well as the sound card for a fraction of a second, then turning them off again. If you're very unlucky, this PSU could damage anything in your computer as well as whatever sits between your sound card and the speakers (some HiFi equipment, usually). I can not even rule out that it might cause a fire (by igniting itself), although the chances are small that this happens.

You better pull out the power plug whenever the computer is not in use (I've had one PSU emit smoke and burnt smell when it was only plugged in, the switch was in the "off" position!), and you should only use the computer with that PSU if it is absolutely necessary.

If you have another PSU that you can put into this computer for testing purposes, you could do that and verify whether the sounds and spinning fans go silent then. If this is the case, that proves that your PSU is the cause of the problem.

If, however, the strange things still happen when you have another PSU inside the computer, then the old one seems to be okay, and something else causes all this. A defective power switch (the one usually found on the front of the computer case, not the one usually found on the back of the PSU) could cause such problems as well, although I think it is very unlikely.



I wonder whether a more powerful one would be necessary. A more powerful PSU usually means more power wasted. I have removed a 250 W PSU from an older computer today and put in a 235 W PSU instead. Now, the same computer only uses about 60-90 W - it used 80-110 W before!

bikerdude on 12/9/2008 at 07:51

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You couldnt be more wrong....

1. it not what size PSU you have its what you have plugged into it that determines how much power is used..
2. also older power supplies are not very efficient, that old crap 250w you mentioned is probably only making 60% efficiency, where as the 500w I put the link up for would exceed 80% - this means the newer psu will actually use less power. Fyi - the old psu you mentioned may have a better efficiency rating than the one before hence the power figures.
3. also arent you forgetting the most obvious point, his system needs a minimum PSU of 400w, putting anything less in not an option.

Aja, trust me just get a new PSU and preferably something slightly more powerful.

biker

baeuchlein on 18/9/2008 at 14:10

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That's not entirely correct either - the PSU is not the thing which determines how much power you need, but it partially determines how much power is actually used. That's the efficiency you mentioned.



Unfortunately, the efficiency of a PSU varies with its load. So, if you place a 500 W PSU in a computer that only needs 250 W, and then you place the same PSU in another computer which needs 400 or 450 W, you may get two very different efficiency values. That's why the advertisement you linked to lists efficiencies with the words "typical load" in brackets.

I have read (but not exactly verified myself) that a PSU's efficiency is usually at its highest when its load is near the maximum. Thus, a 500 W PSU in a computer using just 250 W is usually less effective than the same PSU in a computer using 400 or 450 W. So unless the computer magazine I read is totally wrong (which usually is not the case), one should select a PSU by checking how much the computer really needs.

Meanwhile, I put the 250 W PSU (mentioned in my earlier post) with the apparently lousy efficiency into a second computer which used the 230 W PSU before. This computer now uses about 140 W while it used 130 W before. Apparently, the 250 W unit suddenly is very effective in that second computer which needs more power.



I am very certain that this computer does not need a minimum of 400 W, but rather a lot less. It will, of course, run with that 500 W PSU you mentioned - and it would run very well with even a 1000 W PSU. But whether such a PSU is actually needed is another question.

The second computer I mentioned above can be run with a 230 W PSU. I did that for several months now without any sign of a PSU running hot or the computer being "under-powered". Actually, I calculated power use before I put in that 230 W PSU.

This computer, however, is very similar to the one Aja mentioned. An AMD Athlon XP 3000+, currently running at 2200+, a Radeon 9550 graphics card, an ASRock K7VT4A Pro mainboard, one DVD drive and two hard disks are the main components of this system. As I said, this thing needs 140 W, and that's measured when two programs cut, edit and compress movies while a third one does the same thing for a large audio file. Furthermore, Thief 2 was running to give the graphics card something to do.

Of course, Aja's Radeon 9800 uses more power than my 9550, and his AMD Athlon 2800+ will probably use a bit more power than my "under-clocked" 3000+, but these changes cannot mean that Aja's computer would use more than twice the power my computer needs. A Radeon 9550 uses about 32 W (according to Sapphire's internet pages), and another page I found did not actually measure what a Radeon 9800 Pro uses, but measured a P4 based computer with a 9800 Pro running a benchmark at 1024x768 resolution and with Anti-Aliasing and whatever - and the whole computer only used about 210 W.

Therefore, I seriously doubt that Aja's computer ever needed that 400 W PSU, let alone a 500 W monster. And if the magazine I read actually is correct when telling me a PSU's efficiency usually is low when the computer uses much less power than the PSU could provide, putting in a 500 W monster would likely mean a lot of power wasted.

Of course, one would have to calculate the exact power demands on the main power lines (+3.3 V, +5 V, +12 V) to determine which PSU would satisfy these demands, usually ending up with a PSU which is somewhere above what the computer would need in theory. But I don't think anything more than a 350 W PSU would really be needed here.

Call this post a pointless lengthy babble about uninteresting stuff (Aja has already decided not to buy a PSU, but rather a new computer), but I want to debunk this common myth that today's computers need 400 or 500 W PSUs to run. It costs you more money to buy these PSUs and it may cost you money again to pay your bills if the machine you build uses more power that it really needs to function.

Aja on 18/9/2008 at 18:52

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Technically the graphics card only requires a 300W PSU. So I thought I was playing it safe with the 400.