Vintage Synth Repair

my neighbour recently bought a beautiful elgam talisman, but on 
connecting it to a tape in on an old mixer, it went mute. no 
sounds on the headphones, the rhythmbox light doesn't flash 
anymore, but the powerindicator still lights up. So we are looking 
for a servicemanual, there's one for sale on the web, but the site 
is down. Anybody an idea how to solve this? (the owner might 
check in on this forum later, but he's kinda busy right now, so i 
thought i'd post this in advance) (everybody needs good 
neeeeighbours dumdumdum...)