There are a few things I've learned from the 150 multicart.
One...bad design. If you take it apart, you'll notice stacked cards. Two go to together with several pins on two ends of the boards. If these are not well seated, it will not work or have strange issues with sound, video and just not working at all. If you take it apart, just mark which side is the correct side to match your arrow up.
The reason why the pins inside come apart has to do with the design of the entire thing. The connector that goes into the MVS board will cause the board to flex which slowly causes the pins to pull apart. I just started using the card without the case. The case also is slightly limited on how far it can be seated. I think this is a potential issue as well.
Last thing...This multicart requires more power than a standard cartridge. See if the cart works on it's own without any other cart in the other slots. Use slot 1 to begin with and walk down the slots until it works. The voltage draw may not be "as designed" but more of an issue with cheap / lazy / ignorance. The fact that they have a million extra plus / super plus / extra cool games seems pointless.
The cart overall is cool as long as its working.
Hopefully that helps you.
I just found the pin connection issue last night, so it's fresh in my mind!
-jot3