Donkey Kong cocktail sound issue

Just got a beautiful DK sit down. the only problem is after about 10 minutes the sound volume drops considerably on it's own, but doesn't go away completely. my thought is that something is heating up and screwing something up. I thought I'd ask for some ideas before I go troubleshooting on my own.
thanks

me-only really know mvs but

I'd check the 12volt on the power supply first..(check it with a digimeter when the sound is ok and then when the sound drops..

Could also be some sound chip,bad solder joint loosening after the board heats up..
you could try running a fan,cool air into the machine on the pcb and see if the sound still drops if cooled ..

The audio amplifier for that game is located on the monitor chassis. You may want to look at a cap kit, which should include those that are used for the amplifier.

thanks for the input guys. I'll be checking it out soon. if the its the 12 volt then what should i do? i'm not too savy when it comes to power supplies.
thanx

Either put an aftermarket replacement one in or look for an original on eBay....

They are pretty complex switching power supplies to try & fix.

RJ