Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, the described symptom almost always point to an internal hardware issue or more particularly, possibly auto-protect mode is kicking in where potential suspects after a review of the Service Manual are:
All of the above would require that the SA-BT330 be opened up for visual inspection, voltage/continuity/resistance checks, confirm faults and effect repairs.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even perhaps a soldering iron?
Please post back how you would want to approach this and/or should additional information be needed.