Magneplanar 1.6 QR's problem

Make sure the jumper is tight, (and/or even installed).

Mofi is right - check the tweeter attenuator jumper. Also take the fuse from the working mid/high speaker and install it into the questionable speaker to be sure.

you can take the back plate off easily and look around for loose connections etc, if you have not done so already...

OK I have swapped fuses between the speakers, removed and reinstalled the jumpers and still no change. I will get new fuses today but that's not it. I called Magnepan and hope to get a return call to see if they can offer advice. I'm puzzled.

The only possibiliy i see, apart from a broken resistor or connection in the crossover is the cable which runs from the crossover to the quassi ribbon section. Easy to analyze, just unscrew the crossover plate and tilt it out. To see the connection to the QR, you have to remove the side rails, untack the bottom cloth and strip them ;-)

Do your Maggies have a magnetic strip on the back that stabilizes the ribbons during shipment? If that strip is not carefully removed you will be getting diminished sound quality. I know from personal experience!!