UPB UMC-DB9 Crash and burn

pete_c

Guru
First time I have seen this happen.  Here utilize mostly HAI UPB PIMs and SA UPB PIMs (serial and USB)
 
I was there.  I saw a flash from the UPB PIM and the short flipped a breaker.
 
The PIM is old but didn't ever expect this to happen.
 
I took the UPB PIM apart and took some pictures which are attached.
 
UPB.jpg
 
Nothing attached Pete.
 
Yeah, I would have never expected a PIM to fry like that.  Never heard of any UPB module frying.
 
Yes here only seen something similar happen with an early generation Z-Wave switch.  Only lamp module was behind a coach and the flash was brighter as it scorched the outside of the case.
 
I happen to be in the same room, heard a pop and saw a flash (periferally).
 
This is the sort of thing where having an electronic device meet UL safety standards can make a difference.  It would take me a while to dig up the applicable standards, but one requirement is that the materials used for the circuit board and enclosure do not sustain a fire, and also do not allow it to spread outside the enclosure.
 
When manufacturers don't use the proper materials, it very well could burn the house down.
 
Hard to tell what the component was... an MOV, perhaps?
 
The UPB PIM was plugged in to a metal box / cover on a cement wall. (basement).  Everything is black in the corner. 
 
While the plastic case is blackened it is not melted.
 
UPB tech support said this is the first of it's kind that they have every seen (pictures of).  He initially mentioned a leaky capacitor might be at fault.  I do not see one so it probably is the MOV.  Is it easy to replace?
 
pete_c said:
The UPB PIM was plugged in to a metal box / cover on a cement wall. (basement).  Everything is black in the corner. 
 
While the plastic case is blackened it is not melted.
 
UPB tech support said this is the first of it's kind that they have every seen (pictures of).  He initially mentioned a leaky capacitor might be at fault.  I do not see one so it probably is the MOV.  Is it easy to replace?
 
MOVs often exhibit that kind of self-destructive behavior in response to a large surge.
 
If there is no severe damage to the circuit board or surrounding components, whether it is a MOV or capacitor, it should just be a matter of removing the remains of the old part by unsoldering the leads, and soldering in the replacement.  Just need to know the specs on the part so you get an equivalent replacement.
 
Thank you RAL.  SA tech and I emailed back and forth and he said it was probably the MOV.  I do not know what that looks like as I have never replaced one.
 
Part of the ground terminal melted and the caps look fine...just all black...
 
I want to try fix it if I can...
 
MOVs look a lot like ceramic disc capacitors.
 
MOV-14D221K.jpg

 
As a first step, I would unsolder the remains of the old one and clean up the circuit board as best you can to make sure there are no shorts.  Then try it out and see if it still works. That would indicate there is no other damage.  If it doesn't work, then there's probably no sense in trying to go further.  It won't harm anything to operate it without the MOV.  It just won't have any protection against a future surge.
 
If it still works, then you can order an appropriate replacement.  Since it goes across the AC line, you need one that can handle a Maximum Applied Voltage of 120VAC (RMS) or a bit higher.   This one looks like it would be about right, but you'll need to check the physical dimensions to make sure it will fit.  It's 20mm in diameter.  You can purchase it on Amazon for about $5 (qty 1).  [Edit]: Mouser charges something like $7.99 shipping, but the MOVs are only $0.20 each.  So if you buy 2 or more, it's a better deal.
 
Thank you Ral!
 
Yes it is the MOV...see picture.
 
There isn't much left to it and it's a bit melted.  The black components near by all look fine other than being black now.
 
The center ground post of the HV power is melted a bit at the tip and eaten away on the MOV side.
 
Good thing that this device was plugged in to an outlet on cement in the basement.  The last time (with Z-Wave lamp module) it scorched the couch in front of it and the light was so bright that the couch looked to have a halo around it.
 
The surge caused one 1U server power supply to go belly up and the server was plugged in to a UPS before it tripped the breaker.
 
Dislike this spontaneous electrical combustion stuff.  SA Tech mentioned that he has not seen this happen to any SA PIM in the last 5 years.  I have only a USB SA PIM and rest are HAI UPB PIMs.  The HAI PIM was plugged next to the SA PIM and it continues to work fine. (same circuit).
 
mov.jpgmov2.jpgmov3.jpg
 
Pete
 
I would check the voltage in that AC outlet and maybe a few others around the house. We had a problem here once where the entire street service was low below 110 volts.
 
Mike.
 
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