Faulty PSU or something else?

D_Brasted

D_Brasted

D_Brasted

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10 Oct 2003
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438
Hi,

I bought a Corsair HX620W back in May 2008. Around July my 3.3V rail began to drop, causing instability and forcing me to RMA the PSU. I received a new PSU a few weeks later, installed it with no problems, and have until recently been perfectly happy with it.

In the last couple of weeks I've purchased a second-hand 7600GS, which at first ran with no problems at all. It was a nice step up from my old GeForce2. :) However, a few days ago I began to get stability problems, with random BSODs and occasional restarting. At first I thought it was the new card, and updated DirectX and the gfx drivers (to 94.24, recommended as the best for the 7600GS on the NVidia forums), but it didn't help. The crashes became more frequent, and now included the monitor turning off by itself - I could only turn it back on by restarting the computer.

Still thinking the problem was the card, I reinstalled my old GF2, which has been ultra-reliable for years. No joy - still the crashes, restarting, and monitor shutting off. And in addition the computer would occasionally lock up, requiring another restart. On a whim I checked Asus Probe (I know it's inaccurate, but it gives a rough idea) and my 3.3V voltages were once more being reported as hovering around the 2.6V mark! So it's probably not my new gfx card causing the crashes - it's my PSU. Now the rail's dropping so low the computer won't even start up, or if it does it just locks up, even in safe mode.

I'm going to RMA the PSU again - however, I'd be very grateful if anyone can suggest any ideas as to why only the 3.3V rail has dropped. The other rails are all within spec. Could anything cause the PSU to degrade like that? Or is this a common issue with Corsair PSUs/the HX620s?

For your information, I'm running a P4 2.6Ghz, Asus P4P-800 Deluxe mobo, 2 Gb RAM, 2 IDE hard drives, DVD drive and CD writer (both IDE). It's not like I'm heavily stressing the PSU! :)

Thanks.
 
You really need to test the PSU in another PC to be sure but it could be the mobo as that's what predominantly uses the 3.3v line. No idea why it would initially be fine and then tail off unless the mobo is slowly killing the PSU.
 
Can a mobo slowly kill a PSU? I've always thought if there was a problem then it'd just go "pop" and kill the PSU the moment you turn it on... And why only the 3.3V rail? Unfortunately I don't have another PC to check the PSU in.
 
Well it could if the mobo is somehow shorting the 3.3v line, the PSU would then be trying to power correct the low volts which in turn would put it under strain.

Thing i can't really get my head around is why if the above was the case it worked fine initially :confused:
 
D_Brasted said:
Is there any way I can easily test whether the mobo's shorting the 3.3V rail?
Click to expand...

Well no and strictly speaking it's not really shorting as else things would go pop.

Try removing/unplugging all unnecessary stuff, so things like case fans (not the CPU fan though :)), extra HDDs, CD/DVD-ROM, even extra sticks of RAM and boot the system up with the bare minimum and see what happens to the 3.3 rail.
 
I was using Asus Probe. I can't check anything now in XP, as the crashing's so bad the computer won't even start up properly... possibly it'll hold together long enough to check the BIOS.

All the other rails were stable, and within spec, so would disconnecting anything connected to them make any difference to the 3.3V rail? I don't really know enough about how PSUs work, but it seems from my problems that it's only the section of the PSU that's delivering the 3.3V that's gone wrong.
 
Yes it would help as power correction sort of steals power from the other rails, well it doesn't but the rails are linked so that when 1 rail goes up it will have an impact which will force another down. Sort of difficult to explain but if you get rid of other stuff from the equation it helps eliminate the removed components.

If after disconnecting things the 3.3v improves then add each component back 1 at a time and monitor to see the impact, make a note of the volts and how they vary as you go along.
 
Jump start PSU and check voltages with multimeter.

Could be also something in motherboard.
Increasing number of errors, crashes and eventually immediate crashes after fresh install were symptoms when motherboard of friend's PC probably cooked up its capacitors or some IC.


IAmATeaf said:
Well no and strictly speaking it's not really shorting as else things would go pop.
Click to expand...
Ehem...

An output short circuit is defined as any output impedance of less than 0.1 ohms. The power supply shall shut down and latch off for shorting the +3.3 VDC, +5 VDC, or +12 VDC rails to return or any other rail.
Shorts between main output rails and +5 VSB shall not cause any damage to the power supply. The power supply shall either shut down and latch off or fold back for shorting the negative rails. +5 VSB must be capable of being shorted indefinitely, but when the short is removed, the power supply shall recover automatically or by cycling PS_ON#. The power supply shall be capable of withstanding a continuous short-circuit to the output without damage or overstress to the unit (for example, to components, PCB traces, connectors) under the input conditions specified in Section 3.1.
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
 
I've just disconnected all but the primary IDE drive - so no secondary, and no CD/DVD drives. BIOS/Asus Probe reports the 3.3V rail as fluctuating between 2.6V and 2.9V - only just enough to power the GeForce2 gfx card I have in there. So considering that the computer booted up okay just now, it would appear that my problems are definitely to do with the PSU not supplying my 3.3V rail with enough power.
 
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