If you encounter thread tubes #1 through #3 and/or #14 through #16 stretching and disconnecting on your Melco machine, here is an alternate method of routing the thread tubes to help prevent the situation.
Re-route the plastic thread tubes 1-3 & 14-16 as shown below. Remove tubes 1, 2, 3, 14, 15, and 16 from the plastic clamp to allow for more slack. This adjustment will help prevent excessive stretching as the needle case moves between needle 1 and needle 16.