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Help - ceramic disc capacitor

Bruce Long

Feb 24, 2017
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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.
 

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shrtrnd

Jan 15, 2010
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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.
 

Bruce Long

Feb 24, 2017
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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.


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

shrtrnd

Jan 15, 2010
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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.
 

Bruce Long

Feb 24, 2017
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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.


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.
 

shrtrnd

Jan 15, 2010
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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).
 

Bruce Long

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

shrtrnd

Jan 15, 2010
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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.
 

Bruce Long

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

Bruce
 

davenn

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Sep 5, 2009
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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
 
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davenn

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Sep 5, 2009
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OK yeah a 0.1uF capacitor

the 2 caps and 2 inductors are a noise filter for the power line
 

Bruce Long

Feb 24, 2017
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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
 

73's de Edd

Aug 21, 2015
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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



 
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73's de Edd

Aug 21, 2015
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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
 

73's de Edd

Aug 21, 2015
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Definitely replace it . . . . it has been " far" damaged on one side.
 
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