Dell MK463 N750P-00

[bronchitis]

Hello

I have a Dell Precision 490 which I posted about here (I kindly ask that you read it because it describes the problem I was having with it): https://www.badcaps.net/forum/showthread.php?t=83786

I admit I've done a little bit of a bad job on the motherboard capacitors. I've ordered new ones and will be replacing them again when they arrive so that's sorted. I've ordered a desoldering station because it was needed and a soldering iron itself is simply not enough. As suggested, I've opened up its power supply and it looks like one of its capacitors is very slightly bulging. It is the big right one in the second picture I've attached. It is barely noticeable but it definitely is there and I'll try to get more pictures of it.

What needs to be replaced? I think the first thing I should do is remove the tape to see the capacitors' specifications. Thanks for reading.

[yohnsee]

Re: Dell MK463 N750P-00

Hello,
I read the linked post above, and have a few thing that need clarification.
So you started with a computer that does not want to start and beeped.
From here, you put an old VGA card in, and the computer said, there is an error with the PCI-E lane. Then you replaced the capacitors, and moved on to the PSU? This part is not really clear for me, what is the problem with the PSU, when the computer POSTs with it? Or is it working with an other PSU?
To your original post: first check for obvious problems, like are all the pins in the PCI-E slots look okay? Are none of them bent, corroded, etc? Then move on, if the machine itself tells you, the problem is with the PCI-E region, locate it, which ICs belong there? Read trough their datasheet, find the supply lines, measure with multimeter: do they get their working voltage?
In this post, I assume the 2 big caps are the main reservoirs, they operate on 50Hz (or 60Hz), they don't tend to fail often.

[bronchitis]

Re: Dell MK463 N750P-00

Hello,
I read the linked post above, and have a few thing that need clarification.
So you started with a computer that does not want to start and beeped.
From here, you put an old VGA card in, and the computer said, there is an error with the PCI-E lane. Then you replaced the capacitors, and moved on to the PSU? This part is not really clear for me, what is the problem with the PSU, when the computer POSTs with it? Or is it working with an other PSU?
To your original post: first check for obvious problems, like are all the pins in the PCI-E slots look okay? Are none of them bent, corroded, etc? Then move on, if the machine itself tells you, the problem is with the PCI-E region, locate it, which ICs belong there? Read trough their datasheet, find the supply lines, measure with multimeter: do they get their working voltage?
In this post, I assume the 2 big caps are the main reservoirs, they operate on 50Hz (or 60Hz), they don't tend to fail often.

Hello
Thank you very much for your reply. I will clarify it for you!
The computer was given to me about two years ago. It would not turn on when I received it (the motherboard capacitors were leaking). We replaced the capacitors and it actually worked fine. I installed Windows XP on it and even ran diagnostics without problems. After that, it was put in storage, so it has spent the last 2 years sitting there unused.

Fast forward to now, we've taken the computer out of storage and tried turning it on but it displays the errors I mentioned in that post. Keep in mind that its capacitors were replaced and it worked fine before it was put in storage! Weird, right? I only opened up the power supply because a user suggested that I do. I doubt it's the power supply because these motherboards are usually able to detect abnormal voltage and inform the user about it. I've read on several forums that those two big capacitors (which you referred to as the main reservoirs) are usually pretty resilient but then again, one of those caps seems to be bulging.

I have checked the PCIe slot and it seems to be fine. I even gave it a little cleaning, but there's been a graphics card in it all this time, so I'm not sure much dirt could get in. Moreover, I have no clue where to check for the PCI Express NIC bridge error I got.

So basically, this computer seems to have died in the time it was in storage. I really have no clue what it could be and I'm really starting to lose hope. I originally thought I did a bad job at replacing the motherboard capacitors, but this thing worked for a while after they were replaced.

[yohnsee]

Re: Dell MK463 N750P-00

Okey, now the history of the machine is also clear for me.
To make progress in this post about the PSU, I would suggest NOT to tamper with it. If it works fine, don't repair it. But if those caps, and their bulges bother you, replace them. Go ahead, desolder them, order new ones with the same capacity and voltage rating, and with the same physical attributes (diameter, height, pin distance). This should do the trick, and after that you can call it a day for this post, and we can move onto the other, to find the problem on the mobo.

[momaka]

Re: Dell MK463 N750P-00

Regarding the bulging primary capacitor: press on their plastic top to see if the bulging is actually real or not. Sometimes, the plastic cap on top of big caps like that will dome over time from the heat inside the PSU. But if you press on it and it feels soft (i.e. the capacitor top underneath feels flat), then the cap is not really bulging. If you want, you can even carefully cut the plastic on the top of the capacitor to remove it, so you can really see if the cap is bulging or not.

That said, if the capacitors is bulging, then definitely replace it. Unlike older/cheaper PSUs back in the day that used to use two 200V caps in series directly connected to the 50/60 Hz rectified line, the more expensive PSUs use APFC (Active Power Factor Correction.) It's a circuit that provides continuous current loading across the entire sine wave of the input line rather than just charging from the peaks, like non-APFC PSUs. It also boosts the rectified voltage across the caps to usually 370-390V. So those two big caps in your PSU are likely rated for either 400V, 420V, or 450V... and probably connected in parallel. But indeed if you do have to replace them, then it's best to remove the tape to see their labels. If they are rated for 400V, I recommend going up to 420V or even 450V.

I doubt it's the power supply because these motherboards are usually able to detect abnormal voltage and inform the user about it.

That actually rarely happens.
I have not seen a motherboard to date that will detect an abnormal voltage and refuse to boot. Usually, if the PSU issues a good "Power Good" signal, the motherboard will try to boot. If the voltage is too low, you may run into instability issues. And if it's too high, the mobo could get damaged.

I've read on several forums that those two big capacitors (which you referred to as the main reservoirs) are usually pretty resilient

Indeed they usually are - especially in non-APFC PSUs that directly connect to the rectified line. APFC, on the other hand, does stress primary caps a lot more, so sometimes even good Japanese brands can fail if the manufacturer cut corners and installed underspecced caps.

In this post, I assume the 2 big caps are the main reservoirs, they operate on 50Hz (or 60Hz)

Not in this PSU. Looks like there is an APFC circuit in there, so they probably filter 50-100 KHz from the boost coil.

To make progress in this post about the PSU, I would suggest NOT to tamper with it. If it works fine, don't repair it.

Agreed.
If the primary caps are indeed not bulging (i.e. only the plastic tops are bulging, but the cap underneath is fine), then don't replace them. Overall, the PSU shown in this thread appears very well built. Probably Delta, HiPro, or some other major OEM. I see lots of Japanese caps everywhere, so it really should be OK.

[bronchitis]

Re: Dell MK463 N750P-00

Regarding the bulging primary capacitor: press on their plastic top to see if the bulging is actually real or not. Sometimes, the plastic cap on top of big caps like that will dome over time from the heat inside the PSU. But if you press on it and it feels soft (i.e. the capacitor top underneath feels flat), then the cap is not really bulging. If you want, you can even carefully cut the plastic on the top of the capacitor to remove it, so you can really see if the cap is bulging or not.

That said, if the capacitors is bulging, then definitely replace it. Unlike older/cheaper PSUs back in the day that used to use two 200V caps in series directly connected to the 50/60 Hz rectified line, the more expensive PSUs use APFC (Active Power Factor Correction.) It's a circuit that provides continuous current loading across the entire sine wave of the input line rather than just charging from the peaks, like non-APFC PSUs. It also boosts the rectified voltage across the caps to usually 370-390V. So those two big caps in your PSU are likely rated for either 400V, 420V, or 450V... and probably connected in parallel. But indeed if you do have to replace them, then it's best to remove the tape to see their labels. If they are rated for 400V, I recommend going up to 420V or even 450V.


That actually rarely happens.
I have not seen a motherboard to date that will detect an abnormal voltage and refuse to boot. Usually, if the PSU issues a good "Power Good" signal, the motherboard will try to boot. If the voltage is too low, you may run into instability issues. And if it's too high, the mobo could get damaged.


Indeed they usually are - especially in non-APFC PSUs that directly connect to the rectified line. APFC, on the other hand, does stress primary caps a lot more, so sometimes even good Japanese brands can fail if the manufacturer cut corners and installed underspecced caps.


Not in this PSU. Looks like there is an APFC circuit in there, so they probably filter 50-100 KHz from the boost coil.


Agreed.
If the primary caps are indeed not bulging (i.e. only the plastic tops are bulging, but the cap underneath is fine), then don't replace them. Overall, the PSU shown in this thread appears very well built. Probably Delta, HiPro, or some other major OEM. I see lots of Japanese caps everywhere, so it really should be OK.

I chose to leave it as is. I've measured its voltages with a voltmeter and they're perfect.

[momaka]

Re: Dell MK463 N750P-00

I chose to leave it as is. I've measured its voltages with a voltmeter and they're perfect.

Yes, that may be so. But nevertheless, I still suggest pressing on the plastic cap of that capacitor, just to confirm it's not bulging (it probably isn't.) The only reason I stress the importance of this is because when the primary cap(s) of a PSU with APFC circuit goes bad, it will eventually destroy the whole primary side. So if there is an issue, it's good to try to catch it early there. But again, most likely you will find that it's just the plastic top on the cap is bulging and the cap itself is probably OK.

[bronchitis]

Re: Dell MK463 N750P-00

Thanks again for your reply!

I forgot to tell you that I actually checked the capacitor before putting everything back together but... the top, it isn't plastic. The top is metal or aluminum I think. It didn't move when I pushed it. You're referring to the top part, right (where the vent is)?