SMD capacitor on rectified mains

[Refugee]

I was given a free sound bar with built in DAB radio. It was reported that it had gone bang.

I put power on it and a faint fizz was heard but nothing else.
I took it apart and it took a long time but I did get in there in the end.
Out with the power supply board and on turning it over there was the usual black star all over the print. Rather unusually it was between the DC terminals of the mains rectifier.
There was a small rectangular hole in the middle of the patch of soot the same shape as a 5mm SMD component.
I cleaned it up for a better look and it was indeed the footprint of an SMD part 5mm long.
Even the 3.15 amp internal fuse was still not blown for some strange reason and before you ask it is wearing a reputable brand name sound bar.
I track repair fixed it without bothering to replace the capacitor.

Is this our first SMD RIFA?

[ppppenguin]

Seems that class X and Y SM caps are available: http://www.mouser.co.uk/new/vitramon/vis...afety-cap/

I don't quite see how they can ge the necessary clearance distance in that sort of package size.

[Murphyv310]

I just wonder if it was the component at fault here or as Jeffrey says lack of clearance. One other thing could be contamination from adhesive or flux residue exacerbated by insufficient clearance.

[Murphyv310]

Having such a physically small cap after the bridge rectifier would mean around 330v across it. Seems very much a pointless addition, a suitable rated cap should be installed on the AC side of the bridge.

[Refugee]

The main smoothing cap was fine and may well have "helped" blow the track off the board.
Well if that is what they are doing instead if fitting smelly Rifas it will make it easier for us to fix electronic stuff.
Some manufacturers in there service manuals used to say 5mm for the spacing between mains connections in air after doing a repair.

[boater sam]

Mains AC switches have to have a 4mm clear gap.

[Terry]

My distant memory of BS 415 suggests that the minimum creepage distance in air is 8mm.

[Nick]

 With a conformal coating, EN60065:1994, which for European mains of 230V, allows for about 120mil for Class I (protected by earthing) and 240mil for Class II (double isolated).