Bad caps? Or something else?

[Tom41]

My work PC has recently started showing symptoms of 'bad caps' - constantly and randomly rebooting itself, not going through POST when pressing the Reset button etc. I found that inside the PSU, the fan had stopped working - but replacing the fan didn't help. Only when I replaced the whole PSU itself did the problem disappear.

Do you think there were bad caps inside the old PSU? I looked, and there didn't seem to be any doming on the capacitors. One of them had a little bit of yellow-brown stuff on the top, but that could just have been a glue spillage (yellowish glue that holds other components in place).

The guy in the computer store said it was because I was trying to run a Pentium III CPU off a 250W power supply - and you need at least 400W for that kind of chip. If it wasn't the PSU, perhaps the motherboard is slowly failing, but I don't see any doming or electrolyte spillage on there...

[Rainbow]

Re: Bad caps? Or something else?

Probably some of the caps in the PSU were damaged from the heat.
400W is bullshit, when P3 was introduced, most PSUs were 200 and 250W. There are ~150W PSUs in small desktop systems.

[MD Willington]

Re: Bad caps? Or something else?

Agreed.

I ran my P3 733 from a 235W power supply, the "guy" may want to reconsider his opinion with fact.


The guy was looking to make a sale....

[Chris1992]

Re: Bad caps? Or something else?

I am responsible for a PII-400 Klamath sys with an Astec 145W. I'm also responsible for a Celeron 733 (iirc) with a 90W. 400W requirement for PIII is BS.

[PeteS in CA]

Re: Bad caps? Or something else?

What you have in your system in general may be more relevant - "extra" memory (can you have too much? ), added drives, stuff powered by the USB port, etc..

[Chris1992]

Re: Bad caps? Or something else?

Pete has a very valid point that I missed. The PII 145W sys I mentioned has 1 stick of PC100, 1 HDD, 1 CD-ROM, and 1 floppy, along with an All-In-Wonder and 3 more expansion cards. Still is pretty stable. The Celeron 90W I mentioned, has 1 stick PC133, 1 HDD, 1 CD-RW, and a floppy. Very unstable.

[einhverfr]

Re: Bad caps? Or something else?

Regarding PSU's. It does sound like a cap issue in the PSU.

However, let me explain something about wattage of PSU's. The required wattage is going to depend on a number of things including the number of hard drives and/or CDROM's you may have running at once. If you have an underpowered PSU it will usually give you consistant problems while booting or when running many drives at once.

150 an absolute minimum for a small desktop system and one can often find these to be underpowered if any extensions are made. However, I have at least one server for a business running a Sempron and 2 mirrored hard drives (with many writes) on 250 watts. This system also has 2 512MB sticks of DDR RAM the integrated video card, but no keyboard or mouse, and no CDROM. The only issues we have had with the power supply has been with fans crudding up and failing (this is an environmental issue apart from electrical supply and I believe is related to specifics of the dust composition in this building).

[einhverfr]

Re: Bad caps? Or something else?

One more thing.

My guess is that you had an overheating PSU due to the fan failing. This happens. I have seen it happen before for a customer.

With ATX power supplies, this will inevitably cause two secondary issues: The first is that the power output goes bad resulting in all the symptoms you are describing. The issues are that the caps and/or transformer core are overheating and hence the power is not being filtered and/or converted properly (I think-- I am no electronics wiz yet).

The second is that various components in teh PSU will fail due to the added heat. This includes capacitors, integrated circuits, the main transformer, and the like.

In these cases, I have usually replaced the PSU simply because although they aren't that hard to recondition, if the stability of the system is important, I don't want to find more damage later.