I bought an Aiwa AD-6900 on ebay a few years ago for $20 to use for parts to fix my AD-6900 II. The idea was to use the parts I needed, and throw this one away after I took what I needed. After it sat, I didn't have the heart to throw this thing away and I wanted to see if I could fix it. It was in shambles when I got it-The transport was completely dead and did not respond to the controls, the belts were shot and the wrong size, the alignment of the heads were way off, the power switch was broken off, and it was SUPER dirty. I put new belts in it, cleaned it up, replaced the power switch, and was able to troubleshoot the transport problem back to the power supply. After I fixed the power supply, I got it working, but the audio quality was really bad because the heads were improperly adjusted. Luckily, my friend made me a jig to align the heads, and now it sounds great.
Don't throw 'em out, save 'em!!