Without knowing exactly what failed it is difficult to give a full explanation.
However CB 313 is a 3 phase CB whose phases are split to power a range of equipment including EICAS displays, various lights, pack power (in auto and manual), zone contoller, pressurisation, vib monitors, EICAS computer (L) among other things. While some of these seem to reflect your failures they don't explain them all. Particularly the air data and symbol generator failures.
It would seem that you lost a cooling fan. This would certainly explain the loss of the colour display (raster) on the CRTs but not the lines and marks (stroke). As the CRT cooled the raster would have come back again only to fail again as the thing overheated again. (raster generates far more heat
Reading between the lines of the maintenance response it would however seem that you actually lost an entire bus (left gen bus) possibly as a result of a phase trip, which certainly affect the equipment cooling system. This could in turn have then caused the sequential failures you mention as various pieces of equipment shut down as they overheated. Vital equipment would have transfered over to the good bus automatically but some loss of systems including cooling would have occured.
It is unlikely that you ONLY lost a phase as differential protection circuits would have automatically switched out the entire gen.