Smoke From PSU Socket

Tony Duell ard at
Sun Mar 20 14:40:00 CDT 2011

> I was given a DELNI recently, but it did not seem to work so I unplugged it
> for later inspection. I just plugged it in now and it went up in smoke,
> knocking out all the sockets in the house. I have opened it up and the

Presumably this tripped a main circuit breaker. Was it an over-current 
breaker or an earth leakage device (GFI?)? 

> curious thing is that none of the capacitors has or any other component of
> the PSU is showing any signs of damage, there is scorching only around the
> socket itself.

Did any fiuse in the deviec blow? I would remove and test all of them. 
Normally a catastrophic failure in a power supply will blow at least one 
fuse (after blowing numerous expenisve transistors :-))`

Is the mains input sokcet a simple connefotr, or is it the mains filter 
as well? The latter type will have a metal can on the back side, 
sometimers with a scheamtic of the inductors and capacitors inside 
printed on it. 

If the connector does contain a main filter, it's entirely possible one 
of the capacitors decided to short at the wrong moment.

Another possiblilty is leakeage on the socket itself. Dampness might 
cause this (particularly if it was a GFI that tripped, it doesn't take 
much current to do that). Or a conductive trace across the plastic of the 
socekt (known as 'tracking'), caused by arcing or somethign like that.

Obviosuly you need to replace the socket. If it was my devices, I would 
check all the sceicondcutors and low-value resistors on the primary side 
of the PSU to see if I could find a problem there. I'd also check the 
main filter components (f not part of the socket) and do a high-voltage 
insulation text. 


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