Calling Bass 400 Experts - Blown Due to Speaker Cable Not Plugged in Fully

[MikeBoneman]

Hello, I accidentally blew my Bass 400. I plugged things in, warmed up at a low volume. Few minutes into first song there was a spark and burnt smell. I realized what had happened, speaker cable was not 100% pushed into my cab.

I examined and saw a blast mark around a resitor (100 ohm I believe) near the second power tube, resistor broke in half when touched. This resistor seems related to the wire connecting to R311 which got burned off and was hanging loose. My understanding based on a little research is this is related to the heater circuit. Fuse was still intact but had burns on the glass. The board didnt look scorched.

Based on other pics, it appears that half the caps on this were replaced with some gray ones.

I will probably need to take this to a tech but loathe to think about the potential costs! Any thoughts on what could be wrong? I can fix a resistor and probably reconnect to 311, and replace some tubes. I have access to repair and testing tools but anything beyond a little soldering is probably out of my league.

Any thoughts on the possible collateral damage (for example, could all tubes get blown by this?) or insights on what could have happened under the circumstances (like if speaker wasnt fully plugged in, would it cause power tubes to overheat and maybe short the circuit?).

Board (this was before touching the second resitor near the bottom tube and gray caps).

Wire to R311 burned loose.

Blasted resistor.

 

[tbonesullivan]

Was sound coming out of the cabinet when this happened? Is that the only cab you had hooked up? If you were getting sound, it still had a good connection, and it may be that the connection to the cab had nothing to do with this issue.

I would 100% say that needs work by a tech who knows how to work on Mesa amps. Who knows how much other stuff blew up when the resistor and what ever else went.