Any way to tell apart a CPU defect from a mainboard defect?

I have a fairly modern desktop computer, an AMD Athlon II X2 based silent PC, that does not work.

When turned on, it will start physically (all fans are rotating, disks start up...) but not give a signal on any of the graphics ports (DVI, VGA, and HDMI, I tried all three). Also, the reset button does not seem to have any effect.

I have stripped the mainboard bare of all SATA connections, extension cards, and the one 2GB RAM chip to eliminate them as the problem source, but to no avail, so I think it's fair to assume it's either the mainboard or the processor that are at fault.

However, I have neither a replacement mainboard, nor a replacement processor handy to identify which one is broken. The cause of the defect is unknown, so for all I know, it could be both. Therefore, I'm reluctant to buy replacement hardware blindly before knowing more.

Is there any way to further diagnose (or at least get some indication) which component is broken without buying replacement hardware?

Pekka

Posted 2011-01-04T11:55:58.723

Reputation: 2 239

1Are your graphics on-board, PCI or both? – DMA57361 – 2011-01-04T12:25:54.883

@DMA on-board. I think I have a separate one somewhere though, I'll try that out, hadn't thought of that – Pekka – 2011-01-04T12:27:32.647

Answers

From Motherboard, CPU and RAM Troubleshooting, if you do not get any beeps but can hear the fans, then it is probably a motherboard failure (but do read this on-line book entirely). Some of the tests require having some spare-parts on hand, so can be better done by a tech-shop.

See also Laptop CPU Failure Analysis and Solution can be helpful with its discussion of "CPU rust". (Link is dead.)

harrymc

Posted 2011-01-04T11:55:58.723

Reputation: 306 093

11i like the last step ... CPU swap work ? :) – Run CMD – 2011-01-04T12:49:29.050

@harrymc, nice chart! I personally would follow the chart in that order though. Swapping a CPU is easy enough (if you have extra hardware), that would be my first step. – ubiquibacon – 2011-01-04T13:52:05.417

5Basically to make a long story short "you can tell, but not without swapping one or the other parts first. 9 times out of 10 it is the motherboard though" – Shinrai – 2011-01-04T15:22:56.077

3The question stipulated "Is there any way to further diagnose (or at least get some indication) which component is broken without buying replacement hardware?" So he isn't asking about how to troubleshoot if he has them. Your answer rests ultimately on having them. I suppose the answer is most likely No! But if anybody is so brilliant as to have an answer to the question the questioner asked, then that'd be interesting! – barlop – 2011-01-06T15:13:51.470

@harrymc then he's a silly billy.. Whether he's happy or not, you ignored a key point of the question. If he had any sense he'd be able to troubleshoot if he had replacement parts. Most of that flowchart, with seeing conflict resolution chart, and motherboard performance chart, (not sure who does that), or dealing with the ram.just not relevant.Your answer at the end was swap the part. That's the real answer if he had the part.And it's obvious. And he said he doesn't.If he's happy with your answer then that's his problem.He can amend his question. You are ridiculously lucky to have 15 votes. – barlop – 2011-01-06T15:22:14.533

He did say "is there any way to further diagnose (or at least get some indication) which component is broken(CPU or motherboard) without buying replacement hardware?" it's not even clear how the flowchart even answers that. An answer mentioning a tech store could be what they'd do if they didn't have replacement parts. But your answer involved what they'd do if they did. – barlop – 2011-01-06T15:48:02.610

@harrymc The answer may well be a No(or assumed no).. and so such an answer isn't useful, but may be correct And perhaps a comment that a tech store or call out guy in the area, would have replacement parts, and he'd know how they'd troubleshoot it, probably same way anybody here would. So the best thing for him is not really the answer of likely No, but a comment. – barlop – 2011-01-06T15:54:05.053

@harrymc I suppose you did answer it somewhat by saying " if you do not get any beeps but can hear the fans, then it is probably a motherboard failure " if that's the case and I suppose it is, then it'd be an answer.. but the flowchart looks not that useful in determining mbrd or cpu (and he's ruled out the psu himself for one reason or another - he may be wrong in that but anyhow). I will remove my downvote. and if you've read and are recommending a book.. then that's a nice touch on your part. If you haven't read the book then that's bad but it looks like you are familiar with it. – barlop – 2011-01-06T16:31:00.373

I've seen a motherboard that would turn on, not beep and then shutdown. If the CPU was not there are all, it would turn on but then not shutdown (still no beep). – j riv – 2011-01-11T19:06:37.787

@Jasen, to be accurate, it was Morris Rosenthal that felt like being an overachiever in 2010. Check out his other charts for even more overachieving.

– Synetech – 2011-06-27T03:42:23.523

Connect an internal PC speaker to the mainboard an listen if there is a 'code'. Look for it in the mainboard's manual

Sebastian

Posted 2011-01-04T11:55:58.723

Reputation: 156

I don't have an internal PC speaker handy, but I will check whether there is one already installed - in that case, it would be mute. Would that be reliable indication that it's the motherboard? – Pekka – 2011-01-04T12:24:11.090

I think you can attach leads to the pc speaker jumpers (use a HD jumper and some thin wire) and connect them with eletrcial tape toa a pair of earbud headphones if you really need to. – horatio – 2011-01-04T18:37:37.370

@Pekka I suppose It may be the power supply. It may even be the motherboard is getting shorted somehow , so you should run it out of the case. What you asked, is not What is the problem. You asked now if it was motherboard or cpu. And before you asked more specifically what was broken. So you're assuming one is broken. your question was which was broken, motherboard or cpu. You should work out what you're asking. – barlop – 2011-01-06T16:37:31.910

@barlop I don't really see your point. I am assuming something must be broken, as I'm not getting a monitor signal; what I need to know is whether there is any way to tell whether it's the mainboard, or the CPU. As said, I have already ruled out the power supply because the fans are working. What is unclear? – Pekka – 2011-01-06T16:40:46.620

1@Pekka well, I don't recall the symptoms of really bad ram how it affects booting.. but you decided it wasn't the ram.. really bad ram like no ram could give beeps from pc speaker if you plug some headphones to it. I guess you had reason to rule that out? like 2 sticks tried each. or something.. And there is some difference between "it doesn't seem to work/not working" and "it's broken". It's worth trying to run the motherboard out of the case. BTW, motherboards dying is common, far moreso than processors doing so. That is me nitpicking, not any good new idea for you not already mentioned. – barlop – 2011-01-06T17:45:06.797

@Pekka the normal way of testing the power supply is swapping the power supply. But I suppose you could suspect the power supply is ok if the fans come on.. perhaps! Anyhow, if the computer suddenly does this and you're down to motherboard and cpu, then motherboard's most likely. Just 'cos motherboards are renowned for that. But without swapping you wouldn't know. Even after swapping there can still be doubts! though with motherboards when they seem to die they probably do die! – barlop – 2011-01-06T17:49:17.293

@Pekka a difference between broken and it just seems to not work. and narrowing things down.. is when a motherboard booted up when removed from the case. Swapping the motherboard or swapping the cpu wouldn't have helped. (swapping the case might have ;-)) But was just more a question of narrowing down where the problem is. Not starting with "something is broken, what is it" even though that's very likely! but sometimes a cause can be more benign. Broken is something I don't think about much when troubleshooting. Just what works what doesn't. Narrowing things down. – barlop – 2011-01-06T18:00:32.180

@barlop We may mean the same thing, but I'm not sure I understand. There are three components: The power supply, the mainboard, and the CPU. If the power supply manages to get energy to the CPU fan, it is extremely likely that it is not the cause of the problem. It is either the CPU or the main board that, if both components are assembled properly, is indeed broken - getting some indicators which one it is, without buying extra hardware, is what my question is about. – Pekka – 2011-01-06T18:03:04.163

@Pekka Well, USB ports can fail because of a bad power supply(i've heard of that).. And the rails needed to get the fans on are only a few of those needed to get the motherboard started up. So in theory - I haven't seen it - but it can make good sense for the psu to get the fans running but not the motherboard. The bottom line is swapping the power supply is how you'd know.. I'm not saying it's the ram, or even that it could be, but i'm not sure if it could theoretically be, so how did you rule out the RAM? And I don't think i've seen a PSU fail in the way I described, it's just a theoretical. – barlop – 2011-01-06T18:07:54.017

@barlop the RAM has already been swapped, and also removed from the board. Trust me, I know what I'm doing :) The board should be emitting a beep if the CPU is faulty; it doesn't emit that beep so it is probably the board in this case. – Pekka – 2011-01-06T18:11:08.570

I have the same problem, and it's a real head scratcher. I removed the main board and noticed
some discoloration on the back near the CPU (which led me to believe the motherboard was to blame), but was still not 100% sure, so I removed all the RAM and powered up the board expecting to hear some beep codes, there were no beep codes.

If the mobo was functioning correctly I should have heard the beep codes indicating a problem with the RAM but still no codes.

I replaced the motherboard and thankfully it was to blame.

Before you go rushing out to replace your motherboard, make sure you give your CPU a proper cleaning (as well as your heat sink), apply a new coat of thermal paste, check the pins and make sure it's correctly seated.

Conor

Posted 2011-01-04T11:55:58.723

Reputation: 21

I will say that my usual test is to pull the RAM and listen for an error as well, but a bad CPU can cause the error not to be generated. However, it's almost never the CPU anyway - unless it's been physically damaged or run at extremely high temperatures, CPUs almost never fail. To put this in perspective, I work for a system builder who ships hundreds of systems a year and we replace probably 10 defective motherboards a year, and only one processor every couple of years. – Shinrai – 2012-06-07T18:26:42.370

Probably motherboard or power supply. Processors rarely broke. PC computers are not made wtih diagnostics in mind. So only way to tell what part is defect is to test every part on working system.

So motherboard model and PSU manufacturer and model?

Also check if motherboard condensators are OK.

john samuels135

Posted 2011-01-04T11:55:58.723

Reputation: 131

Are the fans and what not modulating at all after being turned on? if they are, the processor works and its the mobo, if they are not it is the processor.

Jasen

Posted 2011-01-04T11:55:58.723

Reputation: 391

2I think they work independently, but it can be different with newer systems. – Pekka – 2011-01-04T12:08:58.770

ah, yeah, they do. i was half right. are the fans and what not modulating at all after being turned on? if they are, the processor works and its the mobo, if they are not it is the processor. – Jasen – 2011-01-04T12:11:29.943

nah I think I once got as far as mid windows installation and a crash.. changed CPU and fixed. Also, if fans don't turn on then it could in theory be a bad motherboard. at least you bothered to attempt to answer the question though on what fixes are possible if no replacement parts! – barlop – 2011-01-06T15:13:04.260

"modulate" is an odd word to use here. Are you referring to the fan speed changes that can occur in the first few seconds of boot? (Fans normally start full speed then slow down to levels based on temperature/bios settings) – RJFalconer – 2011-01-08T19:56:19.203

yeah you know how when you first boot a motherboard, that fans stay at one hundred percent and then slow down? Well last time i had a processor fail( i knew it was the processor, id been overclocking it plus i had the system beeps.) The fans stayed at 100 percent speed, and didnt come down at all until i replaced the processor. I dont know if that's the norm, but that is what i experienced. – Jasen – 2011-01-11T16:31:58.490