Kelsenellenelvian Posted June 13, 2010 Share Posted June 13, 2010 OK I was brought a pc to replace the power supply on. When carrying it I heard a rattle in the tower. When I took the side off I found a capacitor in the bottom of the tower. After some searching I found where it used to be. (Very top left of the mobo) Well I thought the pc was dead but I still went through the motions of replacing the psu. Not knowing how long the cap has been off I tried powering up and IT WORKED. EVERYTHING WORKS...What could the original purpose of the capactitor have been??? Why is this mobo still working? Link to comment Share on other sites More sharing options...
Kelsenellenelvian Posted June 13, 2010 Author Share Posted June 13, 2010 Forgot some specs:End era p4 (3ghz w\4gigs ram)Dell motherboardCapacitor:Tall black one6.3v1800uf Link to comment Share on other sites More sharing options...
Guest Posted June 13, 2010 Share Posted June 13, 2010 It's purpose depends on the circuit. Was it alone, isolated on the motherboard; or part of a group of capacitors?If part of a group then it likely served as part of a voltage regulation circuit for the processor—some Gigabyte motherboards seem to have elaborate regulation circuitry with possible redundancies. Capacitors store an electrical charge that can be used to smooth rippling current. The loss of one in several may not matter much with a good power supply, but the circuit will have less tolerance for "dirty" power from less stable supplies.If alone, it may be used to temporarily store current in the case of brief power interruption. When removing the CMOS battery a capacitor can usually feed it enough current to hold its settings for a minute or two.Capacitors can also serve as high frequency filters in analog circuits. This may be the case if it was part of an audio circuit. Link to comment Share on other sites More sharing options...
Kelsenellenelvian Posted June 13, 2010 Author Share Posted June 13, 2010 (edited) It was part of a group of 3. I personally have NO idea what area (Capacity) it belonged to. Like you say it is then most likely in the voltage regulation area of the mobo. (It is pretty close to the proc) Edited June 13, 2010 by Kelsenellenelvian Link to comment Share on other sites More sharing options...
dencorso Posted June 14, 2010 Share Posted June 14, 2010 Can you attach a picture of the mobo indicating the position? Link to comment Share on other sites More sharing options...
CoffeeFiend Posted June 14, 2010 Share Posted June 14, 2010 Very top left of the moboTypical placement for the power components.What could the original purpose of the capactitor have been?Filtering and storing power.Why is this mobo still working?It's merely degraded, not completely broken. In just about any system out there, losing some non-critial parts will do that, kind of like if your air filter on your car fell off, it would still work.Capacitor:Tall black one6.3v1800ufThat's a fairly typical electrolytic cap. We already know it's not on the 12v rail (a 6.3v cap wouldn't tolerate that), and most likely it isn't on the 3.3 either (they'd likely have went for a lower voltage to save money), the -5v has been unused by all boards for quite some time, leaving us with the 5v rail only, and using 6.3v caps on 5v power is very classic (just look at any old thing from the 80's full of TTL logic, it's full of 6.3v caps)Also, it's unlikely that it's really part of any "important" part of the voltage regulator circuitry. The phases of the VRD feed off of the 12v rail since ATX12V 2.0 back in 2003, and this seems like a machine that came out after that judging from the specs you gave us. So the voltage for the CPU, RAM and such parts should be unaffected.The 5v rail isn't used by a lot of stuff these days. Most electronics now operate at 3.3v or lower. The vast majority of the power used by the computer comes from the 12v rail(s), either as-is (fans, motors, etc) or regulated to a lower voltage (CPU, RAM, etc), various electronics feed off of the 3.3v rail. The 5v is fed to PCI slots for sure (doesn't mean individual cards actually make use of it though) and some other various stuff (like analog audio) so it's not that surprising you can get by with not so clean 5v.I'm just wondering how that cap got damaged in the first place. I'd have a good and thorough look at all of the caps on that board (especially around the CPU), chances are some of them are vented. Link to comment Share on other sites More sharing options...
puntoMX Posted June 14, 2010 Share Posted June 14, 2010 Yeah well, it's simple, although you see at the specs 6.3v, it doesn't have to say it isn't from the CPU voltage regulator that puts out some 1.8v tops or so and gets feeded from a 12V line. Note that first you have the voltage regulators lowering the voltage from 12 to some 1.8v and from there you will find the coils and capacitors to get the smooth output desired.To me, it's one capacitor of the 3-fase voltage regulator circuits, so it's not as stable as it should be, and I wonder if the other 2 capacitors are doing their job still.note that capacitors could pop underneath too and not only on top . Link to comment Share on other sites More sharing options...
CoffeeFiend Posted June 14, 2010 Share Posted June 14, 2010 Yeah well, it's simple, although you see at the specs 6.3v, it doesn't have to say it isn't from the CPU voltage regulator that puts out some 1.8v tops or so and gets feeded from a 12V lineThe caps after each phase of the VRD usually have a capacity well below this one (1800uF) being unecessary due to the nature of high frequency switching design -- doubly so for modern designs with lots of phases, and their voltage is also typically lower (more like 2.5v). They wouldn't waste the money on a unnecessarily high capacity cap with also too high a voltage which also takes a larger area of the PCB. I'd bet good money it's not for that Just saying... Link to comment Share on other sites More sharing options...
puntoMX Posted June 14, 2010 Share Posted June 14, 2010 The caps after each phase of the VRD usually have a capacity well below this one (1800uF) being unecessary due to the nature of high frequency switching design -- doubly so for modern designs with lots of phases, and their voltage is also typically lower (more like 2.5v). They wouldn't waste the money on a unnecessarily high capacity cap with also too high a voltage which also takes a larger area of the PCB. I'd bet good money it's not for that Just saying...In the older P4 setups it was normal to use 1500uF rated at 6.4V; I don't think it can be build cheaper other than placing 1000uF capacitors. Note that most of those cheaper capacitors don't even hit the specs they should do, especially after a year or so and with higher temperatures. I don't know what the real reason is (I never build a motherboard myself so to say) that they use those capacitors, but saturation, discharge and charge, voltage leaks, temperature and some factors more have influence on them. You could say that theoretical it would be way to much but in practice it would be way off and just enough. I would guess that the voltage regulators aren't that precise so there could be peaks of 6v although it should output 1.8v.Any way, it's just a guess why they would use the specs that "high", but i can tell you it's from the 3-fase voltage regulator (or 2-fase with some extra filter over that circuit). Northbriges and memory banks use normally (say, on a 40USD end-user board like the Dell) one capacitor, one coil after the voltage regulator. Link to comment Share on other sites More sharing options...
CoffeeFiend Posted June 14, 2010 Share Posted June 14, 2010 In the older P4 setups it was normal to use 1500uF rated at 6.4VBefore the VRD? For sure (ATX 1.3 and before), as they were feeding off of the 5v rail. After the VRD, still quite likely as voltages were higher, and capacitor technology wasn't what it is today. Not that I have any old P4 boards handy. Link to comment Share on other sites More sharing options...
puntoMX Posted June 14, 2010 Share Posted June 14, 2010 After the VRD, really.Any way, the board is now walking on 2 legs and before on 3, this is why it still works . Link to comment Share on other sites More sharing options...
Kelsenellenelvian Posted June 14, 2010 Author Share Posted June 14, 2010 More info:They had some guy put a new cd\dvd drive a couple of weeks ago. (prolly got knocked off then)No other capacitors are loose, burnt or fat.I am getting an error during boot that says "Card-cage fan errror" But after pressing f1 it all works as normal.Could it be a part of the sensor array\area?THANK YOU GUYS for the help! Link to comment Share on other sites More sharing options...
VideoRipper Posted June 14, 2010 Share Posted June 14, 2010 Like already said: capacitors are used for all kinds of things and it's a bithard to see from here where it "Fell off"...Just have a close look on that motherboard for any missing components (whereit could fit); most likely it's somewhere near the CPU as part of its powerregulation-circuit. Greetz,Peter. Link to comment Share on other sites More sharing options...
Guest Posted June 14, 2010 Share Posted June 14, 2010 Check the cable leading from the card cage fan; make sure it is plugged in and working. A BIOS reset may also be necessary.From Dell's support forums:Yes you do have a card cage fan it is between the hard drives. Link to comment Share on other sites More sharing options...
CoffeeFiend Posted June 15, 2010 Share Posted June 15, 2010 Could it be a part of the sensor array\area?Nope, fans work on 12v, and this cap definitely isn't on a 12v rail. It's unrelated. Link to comment Share on other sites More sharing options...
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