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    Dell Precision 490 motherboard

    Hello

    Around two years ago, I was given a Dell Precision 490 that wouldn't turn on. The problem was, like with most old Dells, the motherboard capacitors. As soon as I got it, we replaced its capacitors and I remember installing Windows XP and running Dell diagnostics. It passed all of the tests. I even remember playing some old games on it without any problems. After a week or so, I turned it off and put it in storage. It's been in storage until last week.

    I decided to turn the computer on again and guess what, it beeps twice but there's no video. I've tried multiple PCIe graphics cards and none worked. So I figured if the computer is beeping, it's at least POSTing. I got an old PCI graphics card and actually got video signal but was greeted with two wonderful messages.

    Message 1: Alert! Error initializing PCI Express NIC bridge.
    Message 2: Alert! Error initializing PCI Express slot 2 (this explains why I wasn't getting video with the PCIe video cards).

    I am unsure whether these errors are related to the capacitors. All of the caps *seem* to be fine, but I've noticed that in these motherboards, the crappy capacitors tend to dry up after a while, ultimately causing issues, even if they're not buldging. I once had a motherboard with capacitors that were barely buldging (they weren't even leaking) but still caused problems. I am also suspecting the ones we bought to replace the old ones with are of bad quality. I've snapped a few pictures of the motherboard. The circled capacitors are those which have been replaced.

    Is there someone who happens to own one of these Precisions and had this same exact problem? Do you think it is related to the caps? Should I try replacing them again?

    Thanks for reading.








    Attached Files

    #2
    Re: Dell Precision 490 motherboard

    check the power supply. the power supply could be bad and/or developed bad caps causing issues on the board.

    there is also a red brown cap with a Y vent near the dimm slots. is that another kzg or kzj cap? those are no good and are replace on sight even if they arent bulging and still look good.

    as for the mobo caps, u seem to have used replacement caps that are wrongly sized and wrong esr/ripple specs, so they wont fit through the through-hole of the board and they end up having to be left hanging up above the board. this isnt recommended because it affects the esr of the circuit. the mobo has 4 high switching frequency buck regulators near the center of the board behind the io backpanel. those regulators are sensitive to esr and prefer ultra-low esr rather than capacitance.

    the panny fr caps u used there dont have sufficiently ultra-low esr to work right there. the recommended replacements there should be able to take poly caps. what are the original values of the caps used there and the series? but check the power supply first. if the psu is bad we need to fix that first (post it in the power supply sub-forum) then we may examine the mobo caps if it still doesnt work right.
    Last edited by ChaosLegionnaire; 04-09-2020, 02:44 PM.

    Comment


      #3
      Re: Dell Precision 490 motherboard

      Originally posted by ChaosLegionnaire View Post
      check the power supply. the power supply could be bad and/or developed bad caps causing issues on the board.

      there is also a red brown cap with a Y vent near the dimm slots. is that another kzg or kzj cap? those are no good and are replace on sight even if they arent bulging and still look good.

      as for the mobo caps, u seem to have used replacement caps that are wrongly sized and wrong esr/ripple specs, so they wont fit through the through-hole of the board and they end up having to be left hanging up above the board. this isnt recommended because it affects the esr of the circuit. the mobo has 4 high switching frequency buck regulators near the center of the board behind the io backpanel. those regulators are sensitive to esr and prefer ultra-low esr rather than capacitance.

      the panny fr caps u used there dont have sufficiently ultra-low esr to work right there. the recommended replacements there should be able to take poly caps. what are the original values of the caps used there and the series? but check the power supply first. if the psu is bad we need to fix that first (post it in the power supply sub-forum) then we may examine the mobo caps if it still doesnt work right.

      Thank you very much for your informative reply!

      By checking the power supply, I guess you mean to open it up and inspect it, right? What should I look for, bad caps as well?

      The capacitor near the RAM slots is a Rubycon.

      As for the capacitors being wrongly sized/having the wrong ESR, this is something I've never heard of until you mentioned it, so thank you very much for pointing it out. What should I look for exactly when buying replacement capacitors? Should I replace them with the correct ones now? Also, have I permanently damaged the board? Sorry for asking this much, I'm very new to this.

      The capacitors in the upper part of the picture are 2200uF 6.3V and the ones in the lower part are 1500uF 6.3V. The values are the same as the original and the originals were electrolytic capacitors as well.

      I've also got a question concerning the equipment for desoldering. Currently, I have a soldering iron that *says* it's 68W, but I doubt it really is. It's an unbranded one. I also have a wick for desoldering but we're going to be getting some sort of pump for sucking the solder. Is this enough for the job?

      Comment


        #4
        Re: Dell Precision 490 motherboard

        Hello again.
        I have opened up the power supply.
        Looks fine to me.
        I've seen at least one cap that has KZE on it. Is that ok?

        EDIT: Actually, I take it back. In the second picture, it seems like the right capacitor has a *slight* bulge. It's barely noticeable and I only managed to spot it after looking at the picture. Is this a problem?

















        Attached Files
        Last edited by bronchitis; 04-10-2020, 06:03 AM.

        Comment


          #5
          Re: Dell Precision 490 motherboard

          the proper way to check for suitable sized replacements would be to measure the diameter of the original caps and the spacing between the two leads. u also have to pay attention to the height of the caps cos if the caps are too tall they may interfere with the installation of the heatsink or the expansion cards in the system.

          the proper replacement caps u can get are chemicon npcap psg series 1500uF 16v 10x16mm and 2200uF 16v 10x20mm polymer caps. im ass-u-ming the original caps in those locations are all 10mm diameter caps?

          for desoldering and clearing the holes, dont bother with a desoldering pump. wont work and u may dmg the board and rip the vias. use a stainless steel needle or pick with the right diameter to fit through the through-holes to clear it. solder wont adhere to stainless steel so u must make sure whatever u use doesnt contain copper, tin, lead, silver or gold. dont use bronze or brass needles or picks as those are copper alloys and still contain copper and they might get soldered or stuck to the board when clearing the holes!

          the soldering iron used must also be at least 80w or more because this is a server/workstation board so im betting it has a lot of copper in it so a high powered iron is needed to melt the solder. also because this board is a rohs era board, it uses lead-free solder so it requires a higher temperature to melt.

          the kze caps are fine and are not known to be problematic. the power supply seems to contain all good quality japanese caps. ass-u-ming again that all the red-brown caps with the Y vent are kze caps. though the caps all seem to have 2006 datecodes so the caps are fast approaching 15 years old though the system hasnt been used so not sure if the psu caps need replacement due to old age.

          another thing u can try is to check the cmos battery on the board. since it was left in storage for a few years, the cmos battery might have gotten weak. a weak cmos battery can cause weird issues on boards. use a multimeter to check the cmos battery voltage.

          Comment


            #6
            Re: Dell Precision 490 motherboard

            Originally posted by ChaosLegionnaire View Post
            the proper way to check for suitable sized replacements would be to measure the diameter of the original caps and the spacing between the two leads. u also have to pay attention to the height of the caps cos if the caps are too tall they may interfere with the installation of the heatsink or the expansion cards in the system.

            the proper replacement caps u can get are chemicon npcap psg series 1500uF 16v 10x16mm and 2200uF 16v 10x20mm polymer caps. im ass-u-ming the original caps in those locations are all 10mm diameter caps?
            Sorry, but I have no clue what size the original ones were. They're long gone.



            Originally posted by ChaosLegionnaire View Post
            for desoldering and clearing the holes, dont bother with a desoldering pump. wont work and u may dmg the board and rip the vias. use a stainless steel needle or pick with the right diameter to fit through the through-holes to clear it. solder wont adhere to stainless steel so u must make sure whatever u use doesnt contain copper, tin, lead, silver or gold. dont use bronze or brass needles or picks as those are copper alloys and still contain copper and they might get soldered or stuck to the board when clearing the holes!
            I have found the following needle set on eBay. Do you think they'll be any good? https://www.ebay.co.uk/itm/8PCS-Holl...0AAOSwJpda1cH-



            Originally posted by ChaosLegionnaire View Post
            the soldering iron used must also be at least 80w or more because this is a server/workstation board so im betting it has a lot of copper in it so a high powered iron is needed to melt the solder. also because this board is a rohs era board, it uses lead-free solder so it requires a higher temperature to melt.
            Can the desoldering station I've ordered be used for just melting the solder? It is 90w and its temperature can be set according to one's needs.




            Originally posted by ChaosLegionnaire View Post
            the kze caps are fine and are not known to be problematic. the power supply seems to contain all good quality japanese caps. ass-u-ming again that all the red-brown caps with the Y vent are kze caps. though the caps all seem to have 2006 datecodes so the caps are fast approaching 15 years old though the system hasnt been used so not sure if the psu caps need replacement due to old age.

            another thing u can try is to check the cmos battery on the board. since it was left in storage for a few years, the cmos battery might have gotten weak. a weak cmos battery can cause weird issues on boards. use a multimeter to check the cmos battery voltage.
            To be honest with you, I doubt it's the power supply or CMOS battery. I'll still check the CMOS battery of course, but usually, motherboards tend to inform you when there's an abnormal power supply or CMOS battery voltage.

            EDIT: I have checked the CMOS battery and it reads 2.74V. After a quick search, it seems like the typical minimum value is usually around 2.6V. Should I replace it?
            Last edited by bronchitis; 04-13-2020, 06:35 AM.

            Comment


              #7
              Re: Dell Precision 490 motherboard

              Before jumping the gun and replacing all of the caps again...

              1st: Since the PC has been sitting in storage for that long, I suggest removing all RAM and re-seating it. Two beeps also usually indicates RAM error, so start with that. I've had this fix many PCs before. If this doesn't seem to do anything, try running the minimum number of RAM sticks the PC can take/boot with (check Dell service manual to see which slots need to be populated for minimum RAM.) Try all of the RAM sticks in this minimum configuration. I've had RAM go bad out-of-the-blue before on me, so I don't take it for granted that it always works. It's rare, but it can still happen - even with the PC powered off and unplugged.

              Also, looks like you already did re-installed the PCI-E graphics card, judging by your posts, so that shouldn't be an issue anymore. However, if you do have another PCI-E GPU, try that too.

              2nd: Many Dell motherboards are known to drain CMOS batteries while in storage. I think some of the service manuals mention no more than 3 years (so even in less than 3 years, the battery can weaken.) With that said, while 2.74V is usually OK for a CMOS battery, I suggest you remove the battery and unplug the PC. If necessary, you may need to move a jumper somewhere to "clear" CMOS settings (check service manual for your machine.) Then start fresh without a CMOS battery and re-enter all settings in CMOS again (that is, provided the PC boots.) Once that is done, then you can re-install the old CMOS battery. If you run into the same issue again, or the PC refuses to boot even after resetting CMOS settings, do try a new CMOS battery.

              Regarding the caps you used (Panasonic FR): they are not quite as low ESR as the originals (likely Rubycon MCZ or similar equivalent), but they should be fine, provided they are genuine and came from a reputable online store (i.e. NOT Amazon or AliExpress, and even eBay for the most part.) With that said, I don't think the caps are the issue here. The only cap you may need to replace is the brown one shown in your picture here:
              https://www.badcaps.net/forum/attach...8&d=1586451659
              That small brown cap appears to be a United Chemicon KZG series, which are known to be problematic. The rest of the board looks fine, though.
              Last edited by momaka; 04-13-2020, 09:27 PM.

              Comment


                #8
                Re: Dell Precision 490 motherboard

                Originally posted by momaka View Post
                Before jumping the gun and replacing all of the caps again...

                1st: Since the PC has been sitting in storage for that long, I suggest removing all RAM and re-seating it. Two beeps also usually indicates RAM error, so start with that. I've had this fix many PCs before. If this doesn't seem to do anything, try running the minimum number of RAM sticks the PC can take/boot with (check Dell service manual to see which slots need to be populated for minimum RAM.) Try all of the RAM sticks in this minimum configuration. I've had RAM go bad out-of-the-blue before on me, so I don't take it for granted that it always works. It's rare, but it can still happen - even with the PC powered off and unplugged.

                Also, looks like you already did re-installed the PCI-E graphics card, judging by your posts, so that shouldn't be an issue anymore. However, if you do have another PCI-E GPU, try that too.

                2nd: Many Dell motherboards are known to drain CMOS batteries while in storage. I think some of the service manuals mention no more than 3 years (so even in less than 3 years, the battery can weaken.) With that said, while 2.74V is usually OK for a CMOS battery, I suggest you remove the battery and unplug the PC. If necessary, you may need to move a jumper somewhere to "clear" CMOS settings (check service manual for your machine.) Then start fresh without a CMOS battery and re-enter all settings in CMOS again (that is, provided the PC boots.) Once that is done, then you can re-install the old CMOS battery. If you run into the same issue again, or the PC refuses to boot even after resetting CMOS settings, do try a new CMOS battery.

                Regarding the caps you used (Panasonic FR): they are not quite as low ESR as the originals (likely Rubycon MCZ or similar equivalent), but they should be fine, provided they are genuine and came from a reputable online store (i.e. NOT Amazon or AliExpress, and even eBay for the most part.) With that said, I don't think the caps are the issue here. The only cap you may need to replace is the brown one shown in your picture here:
                https://www.badcaps.net/forum/attach...8&d=1586451659
                That small brown cap appears to be a United Chemicon KZG series, which are known to be problematic. The rest of the board looks fine, though.
                I have tried 3 different GPUs. I've also tried reseating the RAM and clearing the CMOS, but the errors persist.
                The capacitor you mention is indeed a KZG. The other user had pointed this out to me but I thought they were referring to the other one, which is a Rubycon. My bad!

                Do you think it could be the cause of these issues?

                Comment


                  #9
                  Re: Dell Precision 490 motherboard

                  Originally posted by bronchitis View Post
                  I have tried 3 different GPUs. I've also tried reseating the RAM and clearing the CMOS, but the errors persist.
                  The capacitor you mention is indeed a KZG. The other user had pointed this out to me but I thought they were referring to the other one, which is a Rubycon. My bad!

                  Do you think it could be the cause of these issues?
                  Well, what I'm slightly concerned about is that the KZG cap is not bulging, and KZG caps usually do bulge when they go bad. So the chances of it being bad are on the small side. But if you do have a spare replacement for it, just go ahead and replace it.

                  That aside, was the computer exposed to any vibration while or before being put into storage? Or perhaps getting bumped a little harder into with something else?
                  Again, unlikely to be the issue, but I tend to be suspicious of BGA issues with the CPU socket if a computer was dropped, bumped, or otherwise exposed to more vibration than usual while the CPU had a heatsink on it.

                  On the other hand, the PCI-E slot is controlled by the Northbridge. So if the PCI-E slot is having an issue initializing, then that could suggest Northbridge BGA possibly marginal (sometimes flexing the board from installing RAM can make the issue go away.) On a related note, check the thermal coupling of the NB silicon/die to its heatsink and/or install fresh thermal paste to its heatsink. You can also try inserting a little pressure on the CPU heatsinks and NB heatsink while the board is booting to see if any of the symptoms change. I know all of these sound like very general things to try, but the issue you have doesn't pinpoint what exactly could be the problem, so we will have to experiment and try different things to see if anything changes.

                  Last but not least, check if the PCI-E bus has its 1.2V termination voltage. Should be found on that small TO-252 MOSFET by the PCI-E x16 and first x8 slots (SLOT1-PCIE??). Measure between voltage and the right pin of that MOSFET/regulator (right pin when viewing the device with the tab at the top.)

                  Comment


                    #10
                    Re: Dell Precision 490 motherboard

                    Originally posted by momaka View Post
                    Well, what I'm slightly concerned about is that the KZG cap is not bulging, and KZG caps usually do bulge when they go bad. So the chances of it being bad are on the small side. But if you do have a spare replacement for it, just go ahead and replace it.

                    That aside, was the computer exposed to any vibration while or before being put into storage? Or perhaps getting bumped a little harder into with something else?
                    Again, unlikely to be the issue, but I tend to be suspicious of BGA issues with the CPU socket if a computer was dropped, bumped, or otherwise exposed to more vibration than usual while the CPU had a heatsink on it.

                    On the other hand, the PCI-E slot is controlled by the Northbridge. So if the PCI-E slot is having an issue initializing, then that could suggest Northbridge BGA possibly marginal (sometimes flexing the board from installing RAM can make the issue go away.) On a related note, check the thermal coupling of the NB silicon/die to its heatsink and/or install fresh thermal paste to its heatsink. You can also try inserting a little pressure on the CPU heatsinks and NB heatsink while the board is booting to see if any of the symptoms change. I know all of these sound like very general things to try, but the issue you have doesn't pinpoint what exactly could be the problem, so we will have to experiment and try different things to see if anything changes.

                    Last but not least, check if the PCI-E bus has its 1.2V termination voltage. Should be found on that small TO-252 MOSFET by the PCI-E x16 and first x8 slots (SLOT1-PCIE??). Measure between voltage and the right pin of that MOSFET/regulator (right pin when viewing the device with the tab at the top.)

                    Thanks for your informative replies. They are very much appreciated.

                    No, the computer was not moved at all. It was sitting near a bunch of other computers. You mention vibration, and recently, they've been doing construction work (digging) not very far from me, but I think there's absolutely no way it caused this, because all the other computers are fine.

                    I'll try the other things you mentioned and then post again!
                    Thanks again!

                    EDIT: Keep in mind that even the NIC failed, so as you said, it is highly likely that the problem could be coming from what's controlling them, rather then them. I have tried applying some pressure on the CPU and NB heat sinks but the errors persist. There are two mosfets by the PCIe slots, but they don't have TO252 on them. I measured the voltage between the left and right pin (did I do it correctly?) for both of them and it seemed to vary between 6V and 3.3V.
                    Last edited by bronchitis; 04-19-2020, 07:01 AM.

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