I have had a couple occasions when I though my system was dead. Fortunetly it wasn't. Here are some of the fixes I found:
1. Clean cartridge slot contacts
The contacts are easily cleaned by using a soft pencil eraser. Just "erase" each contact to get the oxidation off. You'll be surprised at how much gunk the eraser will have, most of the time you will need to clean the eraser after only a couple contacts.
2. Clean cartridge contacts
This is similar to the above. I found it easier to remove the chip from the cartridge case. Just be VERY cautious if you do this, I BROKE the plastic piece the first time I tried it. (Hey, I though my system was dead so I had nothing to loose)
3. Clean control panel contacts
This one takes alot of guts to do. You must take apart your system in order to get to the contacts. I will not discuss the "how-to's" of the actual disassembly, but I will say, use CAUTION. After you have gotten to the contacts, just use that eraser again. :o) Pretty simple huh?
4. Reflow cartridge slot solder
Again, this requires disassembly of the system. Both my systems had cracks in the solder for the cartridge slot. The best fix for this is to remove the old solder and resolder with new. This is known as reflowing.
5. Reflow ribbon cable solder
Very similar to #4 except you are working with the two ribbon cables that go to the display pcb and the controller pcb.
NOTE: One of my systems had an sound problem where the sound would cut in and out. I traced the problem back to a cold solder joint in the controller pcb ribbon cable.
UPDATE: In writting the MESS driver, Dan Boris has discovered that there is a sound co-processor located on the controller PCB. It's a National Semiconductor COP411. Seems the Adventure Vision was one of the first to offer such a technical advancement.
Again, I do NOT take responsibility for you damaging your Adventure Vision. If you do not feel comfortable doing the above steps, please DON'T.