TECH: Circuit Breaker/Short Circuit

This may seem like a novice question(s) but I'm still new to the world
of troubleshooting and could use a little guidance. I posted this in
the jukebox forum but this site is more active and the principle is the
same I think.

I have a Wurlitzer 1050 jukebox that has three DC circuit breakers
located on the control box. The -28v breaker tripped. I could reset
it and it would work momentarily but then trip again. I replaced it
and the new one does the same thing. The other two breakers work fine
and there is proper voltage downstream so I think the
transformer/rectifier must be ok.

So the first question is, besides wires touching each other or
grounded, is there something else that I should be looking for? And
second, since this is DC and only flows one way, doesn't that mean I
should be looking for something upstream of the breaker? Or could
something downstream be the culprit?

I've never tried to located a short before so other than visually
looking for bare wires or something like that, I don't really know
where to start.

.