RBS misbehaving in 2 slot?

I have a RBS cart that works fine in a 1 slot but when I pug it into a 2 slot, the sound is muted. I've tried this cart in several 2 slots(3) and yield the same results.
Anybody here experience the same thing?
BB

Check continuity from the M1 to the Z80. That's what someone told me to do and I found a broken trace.