Connect with us

Help - ceramic disc capacitor

Discussion in 'General Electronics Discussion' started by Bruce Long, Feb 24, 2017.

Scroll to continue with content
  1. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Hi,
    Newbie desperate for help repairing this board. Can anyone help id this ceramic disc cap? First pic is of the blown one. Second is identical capacitor different location on the board. Its the big red one.
     

    Attached Files:

  2. shrtrnd

    shrtrnd

    3,804
    509
    Jan 15, 2010
    It's probably not a capacitor, it's probably an MOV (Metal Oxide Varistor).
    Read the lettering on the good one, and that will probably confirm it.
     
    davenn likes this.
  3. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017

    Thank you for your reply. I'll look more into the MOV, but there are no lettering on the part itself.
     
  4. shrtrnd

    shrtrnd

    3,804
    509
    Jan 15, 2010
    Typically, when an MOV fails, you get the catasrophic damage you see.
    A word of warning, while I have seen MOVs fail by themselves, it usually indicates another problem in the
    circuitry that CAUSED the MOV failure. MOVs are installed to prevent voltage spikes from damaging sensitive
    circuitry down the line. (They're supposed to absorb the voltage spike) MOV's come in various voltages. they're rated for peak to peak voltages in the circuit they're designed to protect. If it's installed in a 120VAC circuit, the MOV rating for that circuit would be rated at 160v or above.
     
  5. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017

    Great information. So, if I reinstall a MOV rated higher than 160V or above, should be ok? Interestingly, the fuses you see adjacent appear still intact.

    Thank you very much.
     
  6. shrtrnd

    shrtrnd

    3,804
    509
    Jan 15, 2010
    The MOV is a semiconductor designed to absorb voltage spikes, which can be very quick. A fuse element has to
    heat-up to open, which apparently wasn't as fast-acting as the MOV. As I said, I'd be checking the components
    in that circuit to make sure something else didn't fail before I just replaced the MOV. (And hope that transformer
    wasn't damaged from the fire on the board).
     
  7. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Thanks again - explains the fuse. Yes, definitely needs more testing. Any idea what the two black parts are to the sides?
     
  8. shrtrnd

    shrtrnd

    3,804
    509
    Jan 15, 2010
    They're marked 'L1' & 'L2'
    Typically 'L' designates an inductor (ie: a wire-wound impedance for AC, as opposed to a resistor in a circuit).
    Since they're just wire, wound around a tube, it's really hard to destroy them. The wire however is lacquered, so that
    the windings don't touch each other and short itself out. The reference here being that it's possible, though not probable that the heat from the small fire might have melted some of the lacquer and shorted turns together.
    You can't really test them because an inductor is just a really long lacquer-covered wire, it will read on a multimeter as a short circuit. It's usefulness is in AC circuits like the power supply you're dealing with.
    I can't really tell from your pictures, but the box that was burned next to the MOV looks like it might be a relay (not a transformer as I originally thought).
    A stuck relay would cause the detonation of the MOV, so I'd try to identify that box in case it's something that will also need to be replaced.
    Whenever an MOV goes, my first suspicion is that something else went bad, and the MOV took the hit (though it's
    POSSIBLE the MOV might be the only damage).
    Time for me to leave for the weekend.
    If you need help, ask here for somebody to try to assist you with your questions.
     
  9. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    You're obviously an EE. Would you be interested in taking this on? Would be happy to compensate well for this project.

    Bruce
     
  10. davenn

    davenn Moderator

    13,793
    1,938
    Sep 5, 2009
    0221172032d.jpg


    the grey item to the right of the MOV looks like a capacitor ... a better pic looking directly down on this part of the board would help

    CLEAN up that part of the board first before taking a pic .... use some isopropyl alcohol / methylated spirits and some cotton buds

    Dave
     
    Last edited: Feb 24, 2017
  11. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Thanks. That one has writing on the back so will not be difficult to find. 0221172031.jpg
     
  12. davenn

    davenn Moderator

    13,793
    1,938
    Sep 5, 2009
    OK yeah a 0.1uF capacitor

    the 2 caps and 2 inductors are a noise filter for the power line
     
  13. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    This board is for a mechanical chair. I suspect the transformer is ok, as all other functions work except the base not going back down. Interestingly, it went up but would not come back down.

    I thought it was the remote at first and had that rebuilt. When it still didnt work, I pulled the control board and found this.

    Bruce
     
  14. 73's de Edd

    73's de Edd

    3,068
    1,299
    Aug 21, 2015
    Sir Bruce Long . . . .

    As others have said . . . .Those are Ferrite based RFI / EMI suppression chokes you can see the wire holes for the lacing of its wire turns through them. They should have a 1000% probability of still being totally intact and functionable.

    The whole board needs a good scrubbing down with toothbrush and 409 and possibly a hog hair brush on difficult spots .Even the LEDs have a soot on them.
    Avoid relays and transformers .Then a final rinse off and the attaching a strong cord between PCB holes and some whirling . . . .around the world . . . spins to fling off traces of water. Then, the grand finale would be a quick blow drying, using a big ole leaf blower.

    as already stated by others .... That board end scorched grey ? capacitor needs to be a special X rated type. . . . .it's specs are written on it . . . . hopefully on the non burned side..
    Don't get carried away in upping that MOV rating initially being used . . . it DID its job..
    That presently installed unit appears to be a 130 VL10 or 20.
    Check the diameter of the old unit if 14 MM its a 10 if 20mm its a 20.

    MOV REFERENCING:

    http://www.mouser.com/ProductDetail/Littelfuse/V130LA10AP/?qs=sGAEpiMZZMsb7Mk3aR4n099ly6w4ci7Q

    Thasssssit . . . . .


    73s de Edd



     
    Last edited by a moderator: Feb 24, 2017
  15. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Wow! Thanks much! Will get to it and let you know how it goes.
     
  16. 73's de Edd

    73's de Edd

    3,068
    1,299
    Aug 21, 2015

    Sir Bruce Long . . . .


    Just now caught, that the other pic showed the spec end of that cap . . .with its labelling.
    That verifies a 275V rating at 0.1 ufd and that is a X2 safety capacitor, being directly across AC line voltage.
    That type of safety requirement spec . . .deters away from you finding that cap either exploded or being in the same state of destruction that your MOV was.

    X2 RATED CAPACITOR :
    http://www.mouser.com/Passive-Compo...apacitors/_/N-9x371?P=1ywtglyZ1z0wqusZ1y9kooz


    73s de Edd
     
  17. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Thank you again. Are you saying this cap likely is ok?
     
  18. 73's de Edd

    73's de Edd

    3,068
    1,299
    Aug 21, 2015
    Definitely replace it . . . . it has been " far" damaged on one side.
     
  19. Bruce Long

    Bruce Long

    10
    0
    Feb 24, 2017
    Will do. Many thanks again and have a great weekend.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-