There are a number of important things to check if you encounter problems, including breaking needles, when sewing caps:
1) In your Melco/Bravo/AMAYA OS software, use Tools - Check for Updates to make sure you are running the latest revision of software.
2) Make sure the design has been digitized specifically to be sewn on caps.
3) Make sure the Cap Driver is precisely adjusted.
7) Make sure the bill or brim of the cap isn't obstructing the machine.
8) Presser Foot Orientation - While at Head Up, you should be able to fit a 2mm hex wrench (allen key) between the needle and the presser foot, or, a 4mm wrench between the back of the needle and the inside curve of the presser foot. See example below:
The adjustment below is very sensitive...do not push the top portion of the Presser Foot back or it can come in contact with other parts of the machine during sewing. Move the Needle Case to Needle #1. Then, you can use two pairs of needle nose pliers and with a very slight twist down, the presser foot can be adjusted backward. Then, test the sewout again to see if the needles are no longer breaking.