There were a few problems with the early MB115’s - so when you are checking it out turn all the EQ knobs to 12 o’clock, horn and limiter on, boost and contour off, master volume 3 o’clock, - plug in bass, turn on power, and turn up the channel volume to about 11 o’clock and listen for grill rattle and bad horn sounds. If grill rattles see if tightening fixes it and if you don’t like the sound of the horn turn it off. Good luck, I hope the amp is in good condition. BTW - the newer MB115’s have a small fan and a vent on the back and the older ones don’t - oh, and check the boost too.
