Found a 688 with a capstan belt that needed replacing. Did that, no problem. So now that I have the transport running, every single pot and fader crackles and/or cuts in/out with movement. This unit comes to me from Las Vegas. The layer of dust on the outside was thick. Opening up the case, I blew air out of the chassis and had one heck of a cloud of dust. Thankfully I found a genuine service manual on eBay, which has been helpful. I'd like to run the 688 through all the tests and alignments I can. But I probably need to remove the corrosion on the pots, faders, and jacks so I have a solid path to put signal through. Any advice on what I need to do to clean up and restore this 688 would be greatly appreciated. The service manual is helpful and quite deep, but obviously doesn't cover the maintenance basics on how to clean and get this old electronic gear ready for advanced maintenance. I've got an oscilloscope on the way and am trying to hunt down a Teac MTT or MXT test tape (thanks for the tip, Skywave!). I figure DeoxIT should restore the contacts, but I'm open to hear others' experiences. Is there a standard checklist for assessing an old cassette multitrack's fitness?