Burn mark around track in LED lamp

I've just changed a failed LED 7W GU10 lamp that had been in an outside light. I took the cover off and found a rather interesting burn mark around the negative track.

Each LED device is three LEDs in series (glow at 7 V, 10 mA gives 9.3 V) so the total voltage would have been around 65 to 70 V when running normally.

The board is an aluminium one. The supply voltage is 240 V, 50 Hz. I assume that the voltage available if the LEDs go open circuit is quite big.

I'd never seen a burn mark like that on a board. It seems to be a failure of the insulation between the conductors and the aluminium board.

Yes, really weird - presumably they do 11W versions as well, as there's spaces for another 4 LED's - so quite high power LED's at 1W a piece.

Nigel Goodwin said:

Yes, really weird - presumably they do 11W versions as well, as there's spaces for another 4 LED's - so quite high power LED's at 1W a piece.

Click to expand...

I tried to trace the circuit. It's a bit difficult as the whole thing is white. I think that the 7 LEDs is the maximum number and that the other pads are for alternative arrangements with fewer LEDs, to keep the LEDs evenly spaced and to avoid needing links.

The burned outline of the -ve track shows that LED 10, the one burned in half, shares a negative with LED 11. I think LED11 is the end of a shorter path of LEDs from +ve to -ve.