Atari 1050 mods?

Hi there. I finally scored a piece of disk-based software for Atari 8-bits, so I decided today to test out my atari disk drives to see if any of them actually worked. One 1050 did. The other 1050 doesn't run the seek test when you turn it on, and is invisible to the computer. I removed the actual disk drive from the cabinet and verified that it does in fact work in the other 1050 chassis. While doing this I noticed that the non-working 1050 seemed to have had a modification done (rather sloppily, I might add; I suspect this has something to do with why it doesn't work properly). There is a hand-written silver sticker over what I'm assuming is an EPROM that reads, "Doubler". There is a second Motorola 6810 piggybacked onto the normal 6810, and a couple of jumper wires leading off into the PCB. What was this, and how was it done properly (so I can verify that it's ok)? I have a Percom branded full height disk with Atari SIO connects on that also seems to not work. I think this is because I need to decipher the 4-position DIP switch at the back panel. Any hints? As it is now, the access light repeatedly switches on and goes off again, each accompanied by a moderately loud click. The light is on for a second and then off for maybe two. It doesn't ever stop doing this, and the drive is invisble to the computer. The drive inside is full height, and made by Tandon I believe. ok r.