Sounds like the belt is slipping in the volume control, that's very
common for the Beomaster 6000.
You can try cleaning the belt using IPA (isopropanol alcohol / tapehead cleaner)
and cotton buds. It will only bring a temporary solution to see if the
diagnose holds water.

I can supply an excellent reproduction belt.
Replacing is not particularly difficult.

Martin

This sounds much like my scenario. I have a Beomaster 8000 that is in diagnostics right now with Atlantic Systems in Hanover MA. In the mean time, I purchased a BM 6500 and the Beogram 6500 CD. They sound great.  I also have a malfunctioning BC 9000 and a BC 8004 HX Pro, neither are working.   I would be interested in trading for or buying the BM 8000, should you not have the inclination to pursue repairs.  I can tell you,  NOT to send it to Pyramid Sound in Austin Texas.

My BC 9000 has a broken part on take up reel clutch, which is no longer available for purchase new. I purchased the 8004 HX-Pro on Ebay to replace it, but, it has more problems with it than the 9000, so I will investigate whether the 8004 can donor parts to the 9000 or not. 

The BM 9000 has much sentimental value to me. My dad bought it right before I was born, and I remember toying with it as a kid and listening to music with it all the time growing up. I don't know what has happened to it since then in the time it's been in storage, but it's a rare and powerful machine that generally sells for a lot of money when they do pop up for sale. I'm not sure what it's worth, but because it's non-functional at the moment, I'm unsure if any offers thrown my way will convince me to get rid of it.

I have both the BM 8000 and the BC 9000,  You are speaking of your BM 8000, correct ?   I will share with you Atlantic Systems diagnosis of the problems with my BM 8000 when it comes available.

Yes, I meant BeoMaster 8000 - not 9000. My apologies.