Vintage Synth Repair

I got this one from Ebay and at first I thought it was a dud, but after some research I found out it needs something plugged in the output jack to make it work. Well it works somewhat however when try to play it tries for a split second then hangs, sounding all drum sounds repeadedly til they fade away to nothing. In program mode all sounds sound up when I press either button and it just doesn't seem to want to play what I programmed in. Any suggestions what could be going wrong here?