Solar panel melt down

[admiralslater]

I was taking off my 2, 2003 75 watt BP solar panels to replace them with a single 275 watt LG neon panel . These panels were from before the time of MC 4 connectors so they have junction boxes mounted to the bottom of the panel to make connections in . when we opened one of the boxes the connection block was melted in 3 pieces the diodes where fried in half . The system is properly fused but not blown and there was no indication of heat damage either to the plastic box or either surface of the panel. The wires are still in good condition . My first thought was fire but I would have expected more surface damage ,maybe a small explosion.
What do the boffins think

[Rapanui]

Lightning strike nearby

[admiralslater]

That is of course one possibility, however that connection box was is the only issue

[foggysail]

Fuse intact----no excess current. Possible failure caused by poor connections. Most home wiring fires are not caused by short circuits which would blow fuses/open circuit breakers. But poor electrical connections generate heat and can result in fire.

[Pauls]

Over current will literally break diodes in half. Don't know what kind of fuses you have, if they are slow blow a major current spike could blow the diodes and leave the fuses intact.

[barnakiel]

Something is telling me there was a spike on this system ...

b.

[admiralslater]

The panels were wired in such a way that the good panel was still supplying charge to the battery . The connections in the boxes where still good even after the explosion and the diodes where blown in two. there was no corrosion . This system worked well for 14 years .
I will find out fuse type tomorrow