I am already in contact with Markbass . And they reply in less then 10 min . This is what thy answer
Hi Sammy,
Thanks for writing and for choosing Markbass.
The cabinet doesn't feature a fuse for the tweeter, it would be a rare case of blown tweeter anyway. Please have a check of the VLE filter setting on your combo as it cuts high freq. I'd like to clarify that the tweeter level control featured on Markbass cabinets is a passive filter, this means that it doesn't boost the high frequencies, just controls the highs that are sending from the amp. Did you try to increase highs on the amp (with VLE all counter-clockwise) and instrument and then open/close the tweeter level control to hear the difference.
Please let us know if that helps.
Riccardo