computer not turning on. How to ID bad power supply w/o buying new one?

[8_INCH_FLOPPY]

My Dell 4700 that I've been using for the last 9 years started giving me BSDs every couple of days for a few weeks, and now it will not display anything when I turn it on. The light on the case turns orange and beeps a couple of times. I have already reseated all of the cards/connectors.

I don't know if it is the power supply or the motherboard, and I was hoping that there was some way I could localize the problem without having to buy a new power supply that i may or may not need.

I checked the power supply voltages with a DMM while trying to turn it on, and they were fine, but I don't have a full understanding of the smps and it's failure modes. For all I know, the DC voltages could be fine 99.9% of the time, but the .1% of they go screwy would still crash my computer. My DMM is not reading any AC, but for all I know, the ripple frequency is higher than my meter can measure. I guess I can't really test for the occasional voltage spike. Is there some other way to check this?

There are no suspicious-looking capacitors on my mobo or psu, so I'm not sure how to proceed. I do have access to a square wave generator and an oscilloscope, but I don't know exactly how I would identify a bad capacitor using them.

Any help(Preferably detailed) answering these questions would be greatly appreciated.

[Pentium4]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Power supplies rarely cause blue screens. I'm guessing it's the motherboard, possibly the chipset, that's a pretty old computer. Does it have integrated graphics? Cause if not, it could also be the video card causing issues.

[ratdude747]

Moved.

The 4700 PSU is know for issues. I personally haven't worked on one (the 4700 I was given had the PSU replaced and I gutted the old one for parts) but I do know any standard ATX PSU 250W+ (a 200W might also work) will work if you have a well built (not gutless) PSU handy.

From what I do remember, the suspect PSU has teapo caps that while usually OK in a PSU do go bad in that model (along with a few other PSUs). I'd recap the PSU. IIRC all the values are availble from badcaps.net; if not, Nichicon HE from digikey/newark/mouser is a good PSU cap choice.

Power supplies rarely cause blue screens. I'm guessing it's the motherboard, possibly the chipset, that's a pretty old computer. Does it have integrated graphics? Cause if not, it could also be the video card causing issues.

Not true. Bad PSU caps and the resultant ripple cause very similar symptoms to bad VRM caps on the mobo.

That said, come to think of it, the 4700 mobo's did sometimes use pre-2005 nichicon HM's that are suspect.

[ben7]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

That said, come to think of it, the 4700 mobo's did sometimes use pre-2005 nichicon HM's that are suspect.

Indeed! I fixed one that was BSOD'ing randomly by replacing the HM's - they were bulged. All fixed.

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

I've never used an integrated video card *Ick*. I updated the video card about 5 years ago. You all are probably going to laugh, but I use this computer for gaming about 1/2 the time, and it runs better than my 2 year old laptop.

I have a bunch of old psus that I've pulled from older computers, but I imagine that most of those are busted, and I don't want to spend several hours swapping out bad power supplies and then have one of them fry my mobo or hdd.

Bad chip-set after 9 years? How? Chip-sets don't just go bad or wear out, at least not on a human time scale.

[Pentium4]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Nothing to be ashamed about, Pentium 4's can pump out some games pretty well. My 3.4GHz P4 could play Crysis 2 @ 1440x900 low settings with Vsync on with an insanely overclocked 8800GT. It could also almost max Left 4 Dead 2 at the same resolution. P4 chipsets run hot, it's not likely but possible...especially if it's dusty.

[dmill89]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Bad chip-set after 9 years? How? Chip-sets don't just go bad or wear out, at least not on a human time scale.

It is not so much the chipset itself that goes bad (unless something else frys it) but rather the solder in the BGA (ball grid array) that attaches the chipset to the board cracking from a large number of thermal cycles. That being said this is mainly an issue with lead free solder especially in hot running chipsets *cough*nForce*cough* so it would be more likely in a 4 or 5 year old system than a 9 year old one.

[GnatGoSplat]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Are you saying that it does actually turn on, just doesn't boot or display video and only beeps? Is there any pattern to the beeping? It might be bad RAM. Bad RAM can cause a machine to turn on, but not display any video and just beep. It can also cause BSODs when the problem is less severe. It's rare, but I've experienced RAM just going bad before.

If it has 2 DIMMs, try pulling running one at a time and see if the machine will boot up. If you have only 1 DIMM, try swapping it with RAM from another machine if possible.

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Ok, I'll test the ram. A more detailed description of what it does would be that the fans all run loudly at fullspeed, it beeps twice, and there is no display at all.

[c_hegge]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Could be the Jet engine syndrome (or whatever topcat calls it). Can be a sign of a dead motherboard

[tom66]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Dell Thermal Failure? We have two Optiplexes at work that have the same issue, with no boot. I think both are bad northbridge (BGA, possibly) or bad caps.

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

I disconnected/pulled all ram, hdd, video/networking/sound card so the only two things connected togther were the power supply and the motherboard, and I turned it on like that. I'm Still getting that orange light and loud fan. So, either one, the other, or both are broken. All of the capacitors on both units pass visual inspection. "jet engine syndrome" is a pretty good description of what the fan sounds like now comparted to what it sounded like when working correctly. Can I reflow the bga using a heat gun, if it's a solder problem?

[Behemot]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

You can give it a try, but doing it anywhere else but on soldering station usually means unreliable results. It may get back in weeks or months.

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

What does it mean to be "on a soldering station"? Are you saying that it is more likely to be a lasting fix if I use a purpose-built hot air rework station, as opposed to a heat gun? If so, why would that be?

[Behemot]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Cause you are much better controlling the temperature and you can precisely control how it cools down. Together with heating whole board, you get much less strain in the board and lower chance of premature joints cracking. If cooled too quickly, it can crack even during the very process…

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

I have successfully soldered/desoldered some pretty small chips in some very annnoying packages, but I'm not sure how one would go about doing a bga of that size... Is there a guide you can reccomend to me? Is there a particular chip on this mobo that is known for getting cold solder joints? I'm not a big fan of this idea, since there's no way to visually see what the problem is. I may be the only one, but I wish modern PC boards were still through hole.

[budm]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

"There are no suspicious-looking capacitors on my mobo or psu" Sometime you can hardly tell until you look real close or actual measurement of the ESR. The caps (6 of them in parallel) in the pictures shown capacitance value to be within 20% but ESR were 5 Ohms.

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

To be sure that they are not the source of the problem, I checked all of the caps on the ps and mobo, and they all but a couple had almost undetectable esr. What are the esr specifications of the Nichicon VR(M) series capacitors? I looked at a datasheet, but I coudn't find it.

I noticed that the second, smaller heatsink on the motherboard is tilted sideways. Is the bga under this one a common source of problems, or is it always the processor?

[ben7]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

To be sure that they are not the source of the problem, I checked all of the caps on the ps and mobo, and they all but a couple had almost undetectable esr. What are the esr specifications of the Nichicon VR(M) series capacitors? I looked at a datasheet, but I coudn't find it.

I noticed that the second, smaller heatsink on the motherboard is tilted sideways. Is the bga under this one a common source of problems, or is it always the processor?

By undetectable ESR, you mean very LOW esr, or very HIGH esr?

That heatsink shouldn't be tilted. If it hasn't cracked the edge of the chip die underneath, then the chip has either overheated (and fried) or there is a bad solder joint (maybe more than one).

[8_INCH_FLOPPY]

Re: computer not turning on. How to ID bad power supply w/o buying new one?

Very low, except for a couple that are somewhere between 1 ant 2ohm.