Vintage Synth Repair

Hi all. 

I have two older keyboards that need minor repairs.
One is my Yamaha DX11 which I picked up with a case for $150. It's in great condition but needs the CR2302 battery replaced. Does anyone know the best way to go about this? I've heard you can't just buy these batteries anywhere. Is that true? I am not afraid of soldering. I've done it before. But I don't want to do any jimmy-rigging as some people do, I just want to replace the battery as it should be (soldered in it's proper receptacle on the main board). 

My other question is about a Peavey DPM2, a forgotten digital synth from the early nineties with some interesting and uniquw sounds. It was performing GREAT for the first 10 minutes that I had it. Then the outs started producing a static sound that gradually overbeared the actual output...whihc eventually gave way to complete silence. Did the D/A converters go in this thing? Does this behavior sound familar to anyone, and if so do you think it would be hard to fix? Or shoudl I just sell this thing for parts and write it off?

Thanks in advance for any assistance you do-it-yourselfers out there can provide!

:-)