[SOLVED] What are the possible causes for a PC not turning on?

[zherot]

A friend gave me this old prebuilt PC (hp pavillion m9150la) because it didn't turn on at all, so I disasesembled it and detected a bulged broken capacitor and I replaced it, didn't noticed anything else at all, assembled it again and nope, still doesn't turn on.

The psu has a led on the back that turns green when connected so I don't know if that means the psu is fine because IMO if I press ON and it doesn't turn on at all either the psu is faulty or there is some short or something that prevents the energy flow, probably even on the mobo since a cap was bulged.

What do you think?

 

[Darkbreeze]

If there was a failed cap on the motherboard then there is quite probably other problems with the board as well. Most caps on a motherboard are for the voltage regulator modules (VRMs) and a failed cap might easily allow for damage to other components in the VRM or at any point along the way on that bus, trace or circuit. Even though motherboards and power supplies usually have some protections built in, super cheap PSUs used in a lot of prebuilt systems might lack some of those protections or an OEM motherboard might not be particularly feature laden either and lack good protections which could allow a faulty cap to damage something before other protections kick in.

Or, it might be that the system did come with a very cheap power supply, and that is the reason the cap was damaged in the first place. Besides which, this is a VERY, VERY old system, initially sold somewhere around 2006-ish, making it like 16 years old and basically not of much use these days anyhow because the Core2 duo and Core2 quad CPUs that came in most of those systems are simply incapable of supporting much of anything on modern operating systems or applications, and certainly of no use in any system being used for gaming. I'd probably, much as you might not want to, assume the board is dead and move on. Definitely not worth fixing or investing any money in. Not even in regions where hardware is expensive and hard to come by.

 

[zherot]

If there was a failed cap on the motherboard then there is quite probably other problems with the board as well. Most caps on a motherboard are for the voltage regulator modules (VRMs) and a failed cap might easily allow for damage to other components in the VRM or at any point along the way on that bus, trace or circuit. Even though motherboards and power supplies usually have some protections built in, super cheap PSUs used in a lot of prebuilt systems might lack some of those protections or an OEM motherboard might not be particularly feature laden either and lack good protections which could allow a faulty cap to damage something before other protections kick in.

Or, it might be that the system did come with a very cheap power supply, and that is the reason the cap was damaged in the first place. Besides which, this is a VERY, VERY old system, initially sold somewhere around 2006-ish, making it like 16 years old and basically not of much use these days anyhow because the Core2 duo and Core2 quad CPUs that came in most of those systems are simply incapable of supporting much of anything on modern operating systems or applications, and certainly of no use in any system being used for gaming. I'd probably, much as you might not want to, assume the board is dead and move on. Definitely not worth fixing or investing any money in. Not even in regions where hardware is expensive and hard to come by.

I agree, I just wanted to fix it because of the "puzzle" it represents to me but you are right that is not worth it, also I wanted to fix it for my friend because he is fond of this pc and just wanted to help him recover it but I really think this is gone for good, I will just do a last test to check with another PSU and maybe see if the power button actually works, the problem with this system is the PSU has some special cables to power specific parts of the system ina way that makes it difficult to test other things, for example it doesn't have a connector on the board to power on or reset... there is also a special cable comming from the PSU that powers up a hard drive that can be used as an external hard drive too, its one of those designs that have a lot of nonesensical "features" to impress normies but that actually make them really hard to be repaired or diagnosed even.

 

[Darkbreeze]

Those unusual features aren't there to impress "normies". They are there because they are proprietary and are there to do the same things that connectors on standard ATX power supplies do but in a different way so that you have to buy replacement parts from the manufacturer and can't use aftermarket or standard form factor replacement parts.

In point of fact, I have a system exactly like the one you have there, sitting in the storage off to the left of my workbench. But yours does have a standard 20+4 pin ATX and 4 pin EPS power connectors so you should be able to use a standard ATX power supply for testing purposes, it just likely isn't going to work in the case as I believe (I'd have to double check) that the form factor of the PSU is proprietary and doesn't conform to the dimensions or mounting pattern of any standard PSU form factor, because it's likely proprietary. But a few of these had sub models with small, cheap ATX power supplies as well.

 

[zherot]

Those unusual features aren't there to impress "normies". They are there because they are proprietary and are there to do the same things that connectors on standard ATX power supplies do but in a different way so that you have to buy replacement parts from the manufacturer and can't use aftermarket or standard form factor replacement parts.

In point of fact, I have a system exactly like the one you have there, sitting in the storage off to the left of my workbench. But yours does have a standard 20+4 pin ATX and 4 pin EPS power connectors so you should be able to use a standard ATX power supply for testing purposes, it just likely isn't going to work in the case as I believe (I'd have to double check) that the form factor of the PSU is proprietary and doesn't conform to the dimensions or mounting pattern of any standard PSU form factor, because it's likely proprietary. But a few of these had sub models with small, cheap ATX power supplies as well.

I agree with what you said but with my comment I meant the hard drive that you can "remove" but can't even connect anywhere because it doesn't use an standard USB connector, also the ability to connect and antena there and "watch tv" or having an extra bay to put another external hard drive, I only have the chasis but this came with a screen that can be positioned in very unusual ways that really serve no purpose.

Also the motherboard of this machine doesn't have a power or reset pin, the frontal panel that has the power button is powered up by a special connector that comes from the psu, it's very weird and makes harder to know if what doesn't work is the actual power on button or the psu.

 

[Darkbreeze]

Ok, well, there MUST be something switched to the motherboard related to power otherwise there would be no way for the motherboard to know when to power on and if the PSU didn't get a power good signal back from the board then by spec it should immediately shut off, so there has to be something going to the board to a switch to tell it when to power on and when to power off. Especially since looking at that system I can see that there is really nothing very different in that regard on the one here or in the pics I can see of the model you listed. So, IDK what you got going on but something seems off.

 

[zherot]

Ok, well, there MUST be something switched to the motherboard related to power otherwise there would be no way for the motherboard to know when to power on and if the PSU didn't get a power good signal back from the board then by spec it should immediately shut off, so there has to be something going to the board to a switch to tell it when to power on and when to power off. Especially since looking at that system I can see that there is really nothing very different in that regard on the one here or in the pics I can see of the model you listed. So, IDK what you got going on but something seems off.

Yeah, after searching again I did found out the front panel connector, I disconnected it and tried to start the PC by using a screwdriver but no matter what pins I touched, it didn't turn on.

I leave the image so you can see it.



Also I don't see any switch to turn the PSU on, it only has a red switch to change voltage I believe but no switch to turn on, but it does have a led that lights up when connected.

 

[Darkbreeze]

Post a picture of the label on the side of the power supply and also the back of the power supply that mates up with the back of the case. All PC power supplies MUST have a switch on the back because there is always power present on the 5v circuit so in order to isolate that there has to be a way to shut the unit off otherwise you'd have to resort to pulling the cord out of the wall/unit or unplugging things from the board with power present, neither of which should ever be done until the switch is flipped to the off position.

And, if you've just randomly been touching pins together without knowing for certain that the two you are touching together are the correct ones for the front panel power switch, then it's highly likely you've already cooked something anyhow. But you might have gotten lucky, you never know.

 

[zherot]

Here are the pics :





I doubt I fried anything because I only touched the pins that I showed you nothing else, and nothing happened at all, no reaction, no sound ,not anything.

Also my friend just confirmed to me that to turn the machine on he only pushed the front panel button, nothing on the back this PSU doesn't have a switch.

 

[Darkbreeze]

The switch on the back of the PSU is ONLY used when you need to ACTUALLY cut power to the system, because when the computer is "off", it is NOT really "off". There is still power present everywhere inside the case, it simply is not in a "switched on" state for the motherboard.

I can see the reason why this PSU has no switch obviously present and there are two reasons. One, it is VERY old. Two, it is NOT an "Active power factor correction" unit, which means it's both really old AND group regulated, which is not uncommon for older units. Active power factor correction (APFC) means a unit will automatically detect and change from 110v to 220v or visa versa based on what the input voltage is. Power supplies with that little red switch on the back must be manually switched to the type of input voltage in use.

What country are you in?

 

[zherot]

The switch on the back of the PSU is ONLY used when you need to ACTUALLY cut power to the system, because when the computer is "off", it is NOT really "off". There is still power present everywhere inside the case, it simply is not in a "switched on" state for the motherboard.

I can see the reason why this PSU has no switch obviously present and there are two reasons. One, it is VERY old. Two, it is NOT an "Active power factor correction" unit, which means it's both really old AND group regulated, which is not uncommon for older units. Active power factor correction (APFC) means a unit will automatically detect and change from 110v to 220v or visa versa based on what the input voltage is. Power supplies with that little red switch on the back must be manually switched to the type of input voltage in use.

What country are you in?

I see, it is indeed old. I'm from Mexico.

 

[Darkbreeze]

Well, since you're on 127v grid, the current 110v setting on the PFC switch on the back of your PSU should be right.

Do you have or have access to a volt meter?

 

[zherot]

Well, since you're on 127v grid, the current 110v setting on the PFC switch on the back of your PSU should be right.

Do you have or have access to a volt meter?

Nope, my next step will be to check with anotherPSU I have that I know it's working when I have time, other than that I think I'm done with this machine.

 

[Darkbreeze]

I would not argue with that assessment.

 

[zherot]

I finally could spend some time again on this machine and it was indeed the PSU, another one made it start just fine, it had some issues with the OS which was windows 7 so I just installed windows 10, the video card was faulty too, it showed some artifacts while using the pc and would refuse to increase the desktop resolution from 800x600, when installing the nvidia drivers it allowed the increase in resolution to 1080p but then artifacts in the screen would appear and completely crash the PC, removing the video card solved all of this issues and giving a service to the gpu (cleaning and replacing the thermal coumpound) did not solve the gpu problems, in the end my friend will buy another PSU and I will install it to give his pc back, he doesn't want to invest a lot on the machine so the cpu graphics will sufice for basic stuff like browsing etc.

Thanks for all the help. I will select one of your answers as the solution because you really helped me out a lot.

 

[Darkbreeze]