@loke I used to have one of these back in the 80s, what I would suspect is that they need recapping (replace electrolytic capacitors) by now due to the CRT tech used.
BTW: This looks interesting...
http://atariage.com/forums/topic/223165-watara-vectrex-flash-cart-rewritable-multigame-cartridge-available/ http://www.vectrex.hackermesh.org/index.php/en/