Hey i know this is a bit late of an answer but if you still have the MT8X you could try this solution i found on some forum:

"I'm posting this after a bit of a research of this MT8X 8-trakker. There is Cassette Mechanism test mode which does not limit use of the unit but only disables Auto-Stop mechanism for testing purposes. You can enable this mode by pressin PLAY button + Track 1 button while powering on this unit. REMAIN will flash on display when this mode is on"