Hi Tomasusa,
Check out this link:
http://parts.americandj.com/Pr...tDesc=GALAXIAN%20SKY
American DJ sells most of the parts needed to do DIY repairs. If it were me I'd first probe around with a multimeter to see if I can isolate where the problem is. Just be sure you don't zap yourself while inside and be careful where you point the laser, especially if you pull the diode out of the unit.
Hope this helps!