Siemens D1184 - weird burn

[Rainbow]

Don't know what happened to this board - the -12V supply to the RS-232 driver chip was destroyed, together with some signal trace. Also one leg of 5V filter cap was burnt, the cap was then completely open.
Fixed the signal trace and -12V trace, replaced the cap and connected the negative leg to nearest ground (as the hole was completely burnt). But it didn't work. Then found a completely unrelated scratch on the back which breaked another signal trace - fixed that and the board works fine! The serial port works, onboard LAN works too.
WTF?

More WTF

On the back - WTF happened?

Caps removed

Back - cleaned

Front - cleaned and new cap

Back - wires

[Maxxarcade]

Re: Siemens D1184 - weird burn

Looks like the cap itself shorted out and caused the traces running to it to act as fuses That doesn't happen too often, normally caps just go open don't they?

[Per Hansson]

Re: Siemens D1184 - weird burn

Or the chassi behind managed to touch the cap leads...

[gonzo0815]

Re: Siemens D1184 - weird burn

May be some not galvanically isolated device was pluged in and caused some ground bouncing currents to follow. There is no coincidence that there are many RS232 opto isolators out there.