Hi all, I have a friends CPU which I said I'd take a look at, see if I could fix it. Its symptoms were, when you push the power button the fans spun for about a second then everything dies. I think the power supply unit is gone, but I'm unsure why and this could be a problem.

My plan is to just replace it because I don't have any testing equipment at the moment, so I won't be able to find out what exactly is wrong with it (unless its something obvious like a loose wire or a blown fuse, but that's if I'm lucky and I'd rather not risk opening it when I have no way of testing)

I've put another PSU in the machine, and now when I press the power button it powers up and stays up (yay). But, I have a blank screen to look at (nay). Even though the outputs of both PSU's are the same on the actual box, there appears to be an extra set of wires that powers a certain bit of the board (the on-board peripherals maybe?). Its square shaped and has two black wires and two yellow wires. Like I say with the new PSU, this adapter is missing, I'm guessing that I could take the adapter off the old PSU and with two spare black and yellow wires fit it to the new one?

I'd really like to get this machine working for him as, he paid for me to see a rock concert, and it would be nice to return the favour.


Okay these are the specs;

Intel Pentium D processor
Foxconn P4M8907MA-KRS2H; motherboard
Old PSU ISO-400PP
New PSU ATX-1123B

The New PSU has less wattage only 230 and the old one is 300, but they do have the same amount of outputs, and there isn't much inside that machine, One Sata drive and one Lan card, that's it, no graphics or sound card and I don't think he plans to put anything in it either.

I also have a spare PSU that belonged to a Dell PowerEdge 1400 (missing the square adaptor too from what I can see).

Any advice for this would be excellent.

In a nutshell there several versions of ATX power supplies. That missing connector provides 12V for P4 motherboards. IMO get a power supply designed for P4s. There are adapters available but the 12V rail in this ATX-1123B model may not be designed for the current load required.

Not sure on specifications of the Dell or if this model still uses a proprietary connector but I would not use it either.

Thanks for the reply, I guess he'll need a new PSU then. I wish I could find out what's wrong with this old one though, it may just be that the fuse is blown, which could be a sign of something more serious. Which in turn, means a new PSU will not last long.

I might be able to do a few tests without a multi-meter, but I would prefer one.

A standard test...

If you disconnect all PSU connections with the exception of a fan or HDD you can unfold a paper clip and use it to short the green and one of the black leads on the power plug-in for the motherboard. If the fan or HDD spins, the PSU is producing power. Try both or all of the black ground connections before giving up. Good Luck

Hi

I recommend you take a look at
http://www.playtool.com/pages/psucon...s.html#atx12v4
Lots of nice pictures.

As a rule I don't recommend using a 5.25" drive to Molex 4 pin connector since most older ATX power supplies cannot deliver sufficient current on the +12V rail, or +5V rail (or other supply rail combinations).

I recommend that you verify from any documentation what wattage supply you require. Paying special attention to the max wattage that you are likely to draw from not only each supply rail, but each combination of supply rails. (It is possible that the old supply was under-rated and died due to over loading, although any cause of failure is possible). Then obtain a replacement supply that meets your needs.

If the machine is manufactured by Dell, a large corp, or has a custom supply then you should check the vendor's www sites (or reliable equivalent information source) to determine the correct replacement. Old Dell Optiplex (G series) PC (for example) used custom manufactured PSUs with some connectors that look like normal ATX power supply connectors, however they are wired in a different manner, using a standard ATX PSU without modification to the wiring can result in the destruction of either or both the PSU and the system.

***DANGER***

Unless you are a suitable experienced qualified licensed technician NEVER EVER attempt to open and repair a PC PSU. They are switch mode power supplies. THEY CAN KILL YOU.

Internally the only parts that are generally replaceable (by a licensed qualified technician) with appropriate safety equipment is the internal fan. Due to their complexity, low purchase cost, unstamped components, high density construction, and the time involved is affecting a diagnosis and repair, PC PSUs are generally not repaired and are replaced (with a few exceptions - due to scarcity, known generic faults, etc).

There are various tests that can be performed without opening the PSU.
They will require a dummy load on the output leads of the PSU (unloaded PSUs will not operate normally and may fail), a length of wire to turn the PSU on, a multimeter to measure the supply rail voltages.

Switch mode power supplies can fail for all manner of reasons,
(Aging components/overload on the output side/poor construction/poor quality components/poor design/etc) the list of possible causes is almost endless.

The lethal nature of the PSU is the reason why: it is fully enclosed in a metal case (and yes the metal case is an RF shield), and that the fuse is INSIDE the case (and not user accessible). If the fuse has blown there will be a reason. PSUs are modular by design and as a rule NOT designed to be repaired. the usual course of action is to replace the supply with a correctly rated replacement PSU.

Hope that helps

Chris

I typically test power supplies with a power supply tester.. http://www.aerocooler.com/shop.cart?...rod_id=PWCX124
These give a quick [ PASS / FAIL ] for a power supply so I don't waste time troubleshooting a system. Cost is minimal so if you work on systems this is a good item to have in your tool box. .

Just because a system will power up doesn't necessarily mean all rails from the power supply are working.

The old pentium Ds did tend to drink at the electron fountain quite heavily, so you have to be careful...but, as you say, there wasn't much else in the box. 230 does sound very light and, if you take into account the fact that some cheap power supplies can't even supply their rated power out of the box, 230 is cutting things fine. (My usual 'rule of thumb' is that if I can count up 200 Watts that the machine needs, I multiply that by 1.5 to get the power supply rating that I want...with reputable, branded power supplies you don't need to be this cautious.)

There are power calculators scattered around the internet, which might help in assesing the total load.

The extra connectors initially came in when graphics cards started using mega-current, but, soon afterwards, some motherboards started requiring the extra connector or they wouldn't boot. Check your mobo manual for details, to see if yours is one of those.

farslayer's idea of a power supply tester is a good one, and I keep intending to get myself one, to throw in the toolbox...

cgtueno thanks for the link, that's exactly what I need, that 4-pin connector dubiously named ATX12V or P4, with a 24-pin main power connector, I can't seem to find what ratings I should have though. The supply that came out was 300watts, and this is a store bought PC, so I'm guessing its components should be correct. I've just checked the back of the CPU, and I've found a CE sticker warning of static etc, and it says its a "Hi-grade computer" Output 300w. I know someone giving away exactly this, a 300w ATX power supply with the P4 connector, but they live miles away, I shall have to ask my friend if he's willing to pick it up.

True and like I say, it doesn't have the ATX12V adaptor that the CPU needs, so I know that rail isn't being used. The new power supply is good though, my problem is, its the wrong type.

This could've been the problem then, I don't know much about PSU's (obviously) but I'm guessing an ISO-400PP isn't exactly the best, and since the PC was sealed (you couldn't even install a graphics card without breaking warrenty) then I'd have to guess that the 300w rating that I've found on the back of the PC, is for the PC 'as is' and maybe that power supply didn't live up to its standards.

Thank you all again for your help. (especially that first link, I love to learn!)

Okay, so I've managed to find a power supply with the "P4" 4pin connector, a FSP400-60THN-P. The only thing is this one is 400W, will it fry the Foxconn motherboard? The old PSU had a max rating of 300W, but I've read that wattage is not the most important thing, and indeed if your using a cheap supply that's not terribly good, then you'd aim for a little higher anyway. I'm eager to try this out, but don't want to risk damaging anything. Is it good to go?

Any help developing my understanding, would be great.

Yes it should work fine.

the power rating 300W, 400W, etc.. is an indication of the maximum amount of power the supply can provide if needed. not an indication of how much power it will 'force' into the motherboard..

'Sealed' PCs do tend to work on the day that they were sold, so the power supply rating would have been adequate then, but someone, eg, upgrades a graphics card, that may not continue to be true. (And having a warranty that forbids you from opening the box is a really bad idea for the consumer.)

The new PSU will only fry the motherboard if the motherboard has a short circuit. So, it shouldn't be a problem (I would need to revise that statement if the mobo has been putting out smoke signals), but no absolute guarantees.

If you are interested in the actual power consumption, there are various power rating calculators scattered around the internet (you put in the spec of your PC, it tells you how much it will draw), but they tend to be a bit approximate; do not believe that these things are accurate to the watt, for example.

Thanks farslayer, I wasn't too sure and I thought it best to play it safe, this thing can probably boot from usb, so I think I'm going to have a little fun before I give it back!

I know I couldn't believe it! I was talking to my brother about it and he said it's quite common, I think it's ridiculous. What happens when you want to upgrade the ram, or put in a graphics card? Or do... anything that involves opening the case? It has an empty PCI-Express slot, but You can't use it unless you pay someone to 'fit' whatever it is that you want fitting... which 'they' can probably supply you with (of course)! "Oh and it has to be one of our guys that actually fits it too!" I wonder how many "support" centres there are filled with sales people, hmmm so you want to upgrade the ram... Or how much they charge per call-out for someone to come round, open your case and reseat something? Okay I'm guessing that's what the warranty is for, but who ultimately gets charged for this?

Madness, and I may be a little over the top here, but I'm used to the open source society! Openness and Liberation!

Okay, so I just tried out the 400W PSU and the computer booted fine, straight into Windows, uhg. So I rebooted and was just about to change the boot order to usb, when I got a little sidetracked with the bios and all the pretty options, like CPU Health, which I took a look in. Inside I found the temperatures and noticed the processor' going up, not 'fast' but fast enough for you to want to watch, and it just kept on going. I turned it off before it reached 65c because I saw the alarm in the bios had been set to 70c.

I left it to cool down for a bit and rebooted to see if it happened again and it did. This time it tripped the alarm, I wanted to see if it would level out, but it didn't. I let it cool once more so I could check to see if it had been over-clocked, nope, FSB is at its lowest setting. On the same screen it does have spread spectrum, something to do with electromagnetic interference, and this is set to 15%, I'm not sure if that could cause the processor to overheat, I'm guessing its unlikely? I did also noticed one of the sticks of ram isn't registering. Could this be the problem? A bit hopeful, maybe? I didn't want to keep pushing it, so I haven't tested this.

There is a switch on the back of the PSU that toggles from 230 to 115, I'm guessing that's volts and to do with the input?

This could very well be why the previous power supply is shot, or non working at least. Would something like this blow the PSU's fuse? Everything else in the PC seems fine, nothing else is hot at all, the processor feels a bit warm but its hard to tell exactly how hot it is, when its behind a fan. All the fans incidentally, do actually seem to work and appear fine.

The only things I can think of, is again something's not quite right with the power, or it could be a heat sink problem, but I'm not terribly sure at all?

How would I go about trouble shooting this?

Spread spectrum is likely to be either unhelpful or irrelevant at the moment. Turn it off until you get things working correctly.


a problem, but unlikely to be the problem.

Yes, and getting this wrong is serious.

Yes (if it was set wrongly). Maybe do rather more damage.

The possibility of a heatsink problem needs eliminating. A crap (technical word) heatsink compound that has dried out, or a heatsink that has been disturbed so that the interface is no longer in a good state seem likliest. (Given that you've looked at it, the other likely options of fan not working or too slow or dust build up should have been eliminated.)

Check also that the fan header is fitted correctly and that the bios setting/readings for the fans seem correct.

I take it that you don't have an optical pyrometer for temperature measurements.

Fixed it and Wow this things fast! Its like 2. something GHz with a gig of ram. Damn! I had a quick look inside the case and noticed one of the power cords was resting slightly against the processor' fan, I also loaded the 'fail-safe' settings from the bios and rebooted. Instantly I noticed a big difference and the CPU now idles at about 39-40c. Yay!

One draw back is it can't boot directly from a usb flash stick. It can boot from a usb FDD, a usb cd-rom or a usb zip drive, but not flash? Its even got usb support for keyboard, mouse and usb legacy! Grub shouldn't have any problems booting the stick, it should be able to see it, but I'll have to use a floppy for Grub... Unless, I do have two sata drives with fedora on them (raid). So I think I'm going to put them to good use, and I'll have to make sure I show my friend how cool his computer can look and feel, before replacing my drives with his cwappy 'Windows infected' hard drive. (I've never been able to use the desktop effects in fedora before, this should be good!)