Quick question on peeling circuit board

Discussion in 'General Electronics Chat' started by Newb123, Aug 5, 2015.

  1. Newb123

    Thread Starter New Member

    Aug 5, 2015
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    Hi,

    I have a new capacitor that I can use to replace this cracked one (please see pic)

    I noticed the green board is peeling some sort of clear plastic.

    Question: if I replace the capacitor, is the surrounding board too damaged for it to work at all?

    Second question: can I desolder/solder the capacitor effectively while it's still mounted with the power supply off?

    Thanks in advance

    image_Newb123.jpg


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  2. #12

    Expert

    Nov 30, 2010
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    1) the clear stuff is a water-proofing coat. It doesn't have much to do with function, just survival. You might put it back with some Krylon Clear spray paint.
    That's better than trying to de-solder it with the power supply ON.

    Most of the ugly in that photo is in a shadow. The board looks OK except for something bad in that shadow.
     
  3. bwilliams60

    Active Member

    Nov 18, 2012
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    I would check the trace on the circuit board to make sure it hasn't burned up and created an open circuit. The copper on that left leg looks like it became quite hot as did the capacitor. You can desolder/solder while it is still mounted as long as the circuit is dead and you have good access to the solder points.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    clean the copper that appears burnt, it will not take solder till clean. also, clean all burnt printed circuit board around and between componants, carbon goes conductive when humidity goes up.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I don't see any evidence of Conformal Coating on the posted board?
    BTW that appears it could a MOV, what is the designation letters on the board?
    edit: A second look it does appear there is C.C. !
    Max.
     
    Last edited: Aug 5, 2015
  7. #12

    Expert

    Nov 30, 2010
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    Yes, it does. I have seen capacitors in that position, but they are usually blue with obvious markings. Look to the other side of the black thing for markings which define it.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Plus MOV's tend to 'self destroy' upon over activation!:eek:
    If the E9 is the designation, the Caps appear to be desig C#.
    Max.
     
    #12 likes this.
  9. Newb123

    Thread Starter New Member

    Aug 5, 2015
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    @everyone

    Thank you so much for your opinions and expertise!

    @#12 actually never thought to look behind the ugly 'shadow' which from these new pics may change your opinions?

    From the newer attached pics behind the black disc (insert part here), is this board salvageable after all?
     
  10. #12

    Expert

    Nov 30, 2010
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    Owie! You have some circuit traces to repair!
    I see part of the printing on the part, but not enough to read it.
     
  11. Newb123

    Thread Starter New Member

    Aug 5, 2015
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    This looks like a MOV since it's about to crumble. Does tht impact anything related to the replacement by any chance?
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see some letters on the 'rear' side, if legible, what are they?
    I see on the board it is RZ3? that also smacks of a MOV.
    You could install a higher Value if this has suffered in the past.
    Max.
     
  13. #12

    Expert

    Nov 30, 2010
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    Yes. It means you have to replace it with the same kind of part which has the same ratings as the original.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There is nothing wrong IMO with fitting one with a higher Joule value, the operating voltage level has to be the same, My old GE Transient Voltage Suppression Manual suggests it also.
    They also have to be allied with the correct fusing upstream.
    Max.
     
  15. #12

    Expert

    Nov 30, 2010
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    Sorry. My early training kicked in. :oops: "Never redesign the products during a repair job."
    OEM shoots service man in head for burning down home. :D
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    An excerpt from the GE manual may be of interest.
    Two of the types of Failure can be.
    Overstress near rating:
    When the transient ( peak current or energy) or steady state (voltage or power) are marginally exceeded, leakage current will increase and not stabilize, breakdown voltage will decrease in a similar manner.
    Extreme over stress:
    Applying conditions well in excess of either transient or steady state ratings will cause the varistor to fail catastrophically.

    It is not always realized that it is not always one particular voltage surge that finishes the MOV off, if regularly stressed over time, failure usually results some time in the future as the original specification degrades.
    If it does not blow a fuse, then the MOV is non effective once destroyed and often not detected.
    Max.
     
  17. Newb123

    Thread Starter New Member

    Aug 5, 2015
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    Thank you everybody! I suspect this is beyond my scope at the moment though youtube has some great how-tos on trace repair. This appliance is within striking distance of a gas line so I will definitely need to feel good about my repair skills if/when I attempt. I might practice on an old computer in the basement to start!

    Thank you!!
     
  18. ian field

    Distinguished Member

    Oct 27, 2012
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    The "RZ3" marking next to the black and crispy bit is likely to indicate an MOV. Some manufacturers publish a table of standoff voltage for the mains voltage in effect - once you've sorted that detail out, select a replacement the same physical size (not smaller).

    MOVs take a hit every time they absorb a spike and usually shatter when they fail, burning up like that could suggest inadequate standoff voltage as originally specified.

    Disc ceramic capacitors usually die of a hot spot that cracks it through, you usually get a burn hole through the epoxy coating somewhere around the circumference. They can burn if you hit them with RF - but my money is on it being an MOV.
     
  19. dick56

    New Member

    Apr 27, 2011
    23
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    That looks like a thermistor/VDR/MOV on a board from a swimming pool pump. They burst when the sun shines and the board gets part of a voltage burst from a lighting strike close by. Down in the Palm Springs area, they fail regularly in the summer.
     
    Last edited: Aug 5, 2015
  20. Newb123

    Thread Starter New Member

    Aug 5, 2015
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    Keen eye. Close but.. It's a saltwater chlorinator for the pool. We had a major lightening storm a couple of nights ago and was also fiddling with some breakers throughout the house the day it shorted out. I imagine all these actions compounded the issue
     
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