If I recall correctly, I initially had the exact same MG behaviour after I repaired the traces on my battery-damaged board. I ordered Jed's board, but while I was waiting, I removed and socketed IC31 (quad AND gate; it was the only one I had handy), and voila - the MG circuit was back to normal. I eventually fixed the original board completely, but swapped it out for Jed's board when it arrived.
And yes, it's very easy to miss soldering a pin on Jed's board. I spent a day tracking down a bug that stemmed from one pin I missed (IC27).
Hope this helps...
Andrew