Component ID

Most likely the filter cap for the input or output of that transformer. They do tend to go pop in a big way and make a big stink.

NOPE! The capacitors that "go pop...big stink" are the electrolytics (the ones with the metal can and an embossed symbol, like the one on the other side of the transformer). That embossed symbol, commonly a 'Y' or '+', is an intentional weakness that allows it to fail when the liquid boils, without the metal can becoming a projectile.

The circled yellow device is, as several others have pointed out, an MOV. A capacitor of that appearance would be a ceramic one of very low capacitance. I don't ever remember a ceramic capacitor failing (other than the special ones with a cut in the edge to make them into spark-gap limiters), and if it did fail, it would not explode or vaporize.

Looks like a capacitor to me....

I can't really identify the code on this component but if this is a varister you were close enough. thanks

You are correct! It's a standard MOV.

They only conduct when the potential across them exceeds a built-in limit a bit above the nominal line voltage (in this case we can guess somewhere near 300V). They shunt power surges safely to the neutral / ground line and then stop conducting. With minor surges they may survive several events, but each time slightly diminishes their ability to handle the next one. With major surges, they may not survive beyond the first one. But either way, eventually they overheat and self-destruct - hopefully saving the rest of the circuit.

Definitely an MOV. But if it really vaporized and there is nothing left of it, your PCB is likely toast anyway. When the MOV vaporizes like that (as opposed to just opening), it puts out a "mist" of metal oxides, which then coat everything in the vicinity. Most likely when / if you replace it, other components on the board will no longer function. But it's probably cheap to find out, a little MOV like that is only going to cost a very small amount, as in under $1US.

You are right, when it vaporized it left a mist around it and in the vicinity of the transformer but the only other component that suffered was the transformer primary winding going o/c. I had to clean up the pcb a bit.

Thanks Guys but I made my homework and found that the component is a Varistor like INR14D621. What I found is that the elements in this comp short out and blow the fuse if mains voltage rises from 220V ac and exceeds 385V ac. It also prevents noise (probably they meant transient spikes).

I wonder if it is as efficient on a 240V/50Hz a.c mains supply as that is our utility supply voltage.

Looks like a yellow M&M to me.

I think: