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Help to replace blown capacitors on UPS

  1. May 22, 2012 #1
    Hi there,
    I have a UPS which seems to have blown up two capacitors inside. It is a cyberpower 2200VA UPS

    I was running the UPS from a generator when it must have surged or something ... there were two quite big puffs of smoke that came out of the fan exhaust of the UPS. And then the UPS was dead. I bought the unit second hand and now I am working out in Sierra Leone so there is no chance of getting it fixed on warranty - and very little chance of finding a reliable technician here. So I just wanted to ask some advice... I have basic electronic skills and no problems soldering so I wonder if this is something that can be fixed?!

    I opened it up and I find there are two capacitors that are completely blown and burnt apart. This is all I can see that appears to be damaged (although of course anything else on there could be busted).

    Is it likely that other components would have blown up? Or would the capacitors have blown first and saved everything else?
    If its just the capacitors I just need to replace them with an equivilant, right?
    Here is a photo of the blown components: duff.tv/UPS_blown.JPG

    Any advice is much appreciated. I realise its almost impossible to advise from a single photo .. but anything would be appreciated. Thanks again, Michael

    EDIT: The UPS is not actually completely dead. If I try and turn it on (when not plugged into power point) the lights on the front flash to indicate no power source ... just like they normally would do.
    Last edited: May 22, 2012
  2. jcsd
  3. May 22, 2012 #2


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    You can't break it now, so have at it. Can you read the values off of the destroyed caps?
    That will be key, as you need to get the correct replacements. If you can get the values go online and order the replacements.

    Chances are pretty good that the only thing wrong is the blown caps, they are cheap and easy to replace so even if it does not work after replacement, you have not lost much.
  4. May 22, 2012 #3
    Hi, thanks for that fast response. I can't seem to read the values of the blown capacitors. The outside casing is disintegrated ... I'll try contacting the manufacturer and seeing if they will tell me.
    Thanks again for your help
  5. May 22, 2012 #4


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    OK looking at your photo they are obviously not electrolytic caps that have blown

    they are either disc creamic cap's or MOV's MOV's are devices that look like a disc ceramic cap, they are used to protect against excess voltage spikes.

    I cant see from your pic, a bit blurry and the wrong angle.
    have a look on the circuit board and see what text there is silkscreened by those 2 components. that will be a quick way to determine what they really are

  6. May 22, 2012 #5
    Looks like they may be the Y-capacitors. On the chance that they are, here is some advice.

    Do you have a ohmmeter?
    -Remove the dead parts.
    -Clean PCB with alcohol (or ProClean if you can get it).
    -As davenn suggested look for surviving nomenclature on PCB.

    With ohmmeter buzz between each side of device to chassis. If one side is chassis these are your Y-capacitors. If this is the case these parts are safety critical and, if you replace them, you need to use UL recognized Y-capacitors.
    Their purpose is to mitigate EMI, but because they connect directly from AC mains to human touchable chassis they have this additional safety burden (they are designed so that if they blow they will leave behind no residue that leaves AC mains voltage connected to chassis). If you can't get the correct replacement, you are better off pitching the UPS.
  7. May 23, 2012 #6
    Thanks again,

    OK, on the board it does say MOV4 and MOV2 next to these components.

    I moved one of components just a little bit to see the text on the board and the component just broke off and crumbled leaving only a circular metallic disk. There is absolutely no way I would be able to get a value from the casing the component.

    I can get hold of an ohmmeter next week.

    If these are identified as MOVs is there any way to know which components exactly to replace them with? My girlfriend is travelling to London this weekend and it could be my last opportunity for a while to get components.

    Cheers for the help
  8. May 23, 2012 #7


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    OK thats good to confirm their identity :)

    now, for testing purposes the PSU doesnt need them to operate. Unsolder their remains from the PCB and make sure you havent left any solder blobs shorting out circuit tracks

    Did any of those fuses that can be seen in the pic blow ?
    are there any other components that have obviously blown --- look at the transistors etc on heatsinks and make sure none of them are cracked.

    if all looks OK, you could risk firing up the unit and see what happens.
    Make sure the input voltages are within the limits of what the unit requires

    If it works, awesome, then we can work on the MOV's replacements
    if it doesnt and puffs more smoke from elsewhere, then chances are you are not likely to repair it and you can give it a decent burial ;)

  9. May 23, 2012 #8


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  10. May 23, 2012 #9
    ok thank you for this information.
    To test the fuses and to clean the board I'll

    need a couple days to track down a soldering iron and multimeter here - I will endeavor to do this an be back with an update then.

    I can't visually see any other blown components on the board. None of the other capacitors look blown and the transistors aren't cracked.
    As I mentioned earlier - it appears when I turn the unit on but without any input power it is working as it should (although the batteries are flat).

    Thanks again for the help and I'll be back in a day or two
  11. May 23, 2012 #10
    btw, cyberpower just sent me the service guide which has circuit diagrams on it for this unit.
    I've located on the diagrams two MOVs .. they are in different slots (MOV1 & MOV3) rather than MOV2 and MOV4 like mine are.... MOV1 & MOV3 are empty spaces on my UPS.

    Here is the guide:
    duff.tv/Service Manual_PR1500E-2200E-3000E_V00 _050829_.pdf

    I wonder if you are able to decipher the circuit diagram and advise me on what I should be ordering as a replacement? Even though I haven't yet done the diagnosis you advised I'd like to order these while I have the chance ... otherwise it could be months before I'm out of Sierra Leone.

    Thanks once again,
  12. May 23, 2012 #11


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  13. May 23, 2012 #12
    Next, it sounds like you need to put some more beefy surge protection on the output of your generator.
    Last edited: May 23, 2012
  14. May 23, 2012 #13
    Thanks - will try and find somewhere in the UK that I can order this compoonent. Are there any other things to look for when buying? Or just any 20D471K will be OK?

    I will definetely be upgrading the surge protection and running everything through a better voltage regulator.
  15. May 23, 2012 #14


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    If it has the same part number, it's the same part - it doesn't matter who makes it.

    If somebody wants to sell you an equivalent specification part with a different part number, then you need to be sure it really is equivalent.
  16. Sep 17, 2012 #15
    its been a while, but I finally got a hold of those MOVs and replaced them on the board. All is working perfectly!

    Thanks again for the help
  17. Sep 17, 2012 #16


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    awesome to hear and appreciate you reporting back :)

    I have repaired quite a few switch mode PSU's all protected with MOV's .... often its just them that blow apart, but occassionally the surge was such that it takes out a number of other parts as well

  18. Sep 17, 2012 #17


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    Hey Davenn,
    Just curious where you are that the MOVs blow apart regularly. Do you know what is causing the surge? Does other, non-MOV protected, equipment get taken out? I design switch mode power supplies pretty regularly so I am interested in how faults occur. Our utility is pretty good around here so surges are very rare.
  19. Sep 17, 2012 #18


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    Sydney, Australia

    the surges are usually/mainly caused by lightning strikes in the area. Australia has a pretty active storm season stretching mainly from September through to March
    The last 2 companies I worked for had me spending a lot of time repairing or replacing equip blown apart by lightning induced power surges.
    Our mains power in Australia is pretty respectable as well. The majority of power cuts would again be caused by lightning strikes.

  20. Sep 17, 2012 #19


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    Interesting. Thanks!
  21. Sep 18, 2012 #20

    jim hardy

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    you said you were running from a generator when this happened?

    it is a trait of alternators that disconnecting a large load from them will cause output voltage to rise (briefly) until voltage regulator can catch up. How much? difficult to guess, shouldn't be drastic but if your MOV's were sized close they might have died a noble death trying to contain the transient. What's insignificant to a big generator could be darn significant to a little UPS.

    If this happened when you disconnected a large load like a cooktop or large string of lights, be aware of this generator trait and maybe adjust your operating procedure so UPS is last on, first off... A minimum load for generator might help it avoid using the surge protection you plan to add, perhaps a substantial incandescent lamp that's left always on .

    just a thought. (I assume you ordered a few extra MOV's for UPS....)

    old jim
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