When connected into a phantom powered system, the 48V reverse biases the capacitor and causes trouble. This trouble can be temporary and sometimes it can be permanent. If you re a musician and this scares you, it should. Call the manufacturer and ask. Have a service tech who understands the problem check the schematic.
Electronic keyboards are also suspect.
I ve had other musicians tell horror stories of blown instruments caused by assuming that the balanced outputs on the instrument were phantom power proof. I came up with this idea when I worked at Mackie Designs. It has been incorporated into all of their mixers that have XLR connectors for their outputs. I ll describe the mod in words. This should be crystal clear to a competent service tech.