Great success, big hit
Do you have a source for this 박 being 博? Naver seems to be of the opinion that it’s native (or at least that no hanja can be identified without doubt).
No hanja, it is native word meaning "Great success". Do you know "gourd". 대박=Big gourd. It's a good meaning.
The Internet now says it's actually not 大博 (great scholar) but 大舶 (great ship, when the gourd is really big and your ship has come in). -- https://bridgetokorea.net/archives/1556
Certainly it appears more common: