Assuming Yorkville TX8s, check the solder points on the input board. I had TX4s and had a problem with cold solder joints there. If the problem was with the horn or mid, I would suggest checking the protection network as well but that does not include the 15s. Here is the service manual in case it helps: http://www.yorkville.com/downloads/servman/sm_tx8.pdf?v=1365089965
Come to think of it - I did have a problem a couple of years ago with the crossover in a Yorkville e152.
The horn and woofer were fine...
I took the cab apart and looked at the crossover for burning, etc. and everything looked ok...
I brought it to a local tech (Yorkville authorized dealer) and the tech "touched up" all of the solder connections on the crossover..that was it.
The e152 had been pushed quite hard (on rental).
Hopefully it is something simple like a cold solder issue.
The replacement woofers are expensive.