Being I sold ya the hardware I'll help some... LOL! The cart was never upgraded. That cart came with 1 of 2 Western Digital Controllers, so 2 revisions. I had to crack her open to check which chip, and solder the gold plated leads on. Coco's are notorious for bad connections on the tin plated connector. Most people weren't smart enough to know to replace the connectors, but rather replaced the controller, thinking it died. Learned the trick from someone on a BBS years and years ago...
26-3022
This first model of CoCo floppy controller was packaged in a long cartridge, and was introduced for use with the original CoCo. It uses a WD1793 controller chip, which requires +12V DC. For this reason, a multi-pak interface (or other source of +12V) is required to utilize this controller with a CoCo 2 or CoCo 3. This controller also uses an analog data separator circuit, infamous for its inherent unreliability. However, this controller is the only one capable of being modified (though with considerable difficulty) to allow use with high-density 3.5" floppy drives. All subsequent controllers use the WD1773 controller chip, do not use the unreliable analog data separator, do not require +12V (so they will work with any CoCo model), and are capable of double-density operation only.
As for double sided, all you have to do is type the follow in disk basic. Doing such will allow you to also use both sides of a 3.5" diskette drive!! . If you wish to use a 3.5" diskette, but care less that it only single sided, then it will work without any custom pokes. To use more of the space, you must use the pokes provided below.
As noted, the command is DSKINI# (where # is 0-3, or 0-255 in RGBDOS)
Also, try this poke (DECB1.1, not 1.0)...
POKE55456,68
If that works, you just doubled your storage on the 3.5" floppy. Also Try DSKINI3. You can POKE55456 with 65,66 or 68 to access the second side of drive 0, 1 and 2 respectively, as drive 3.
Other then that, i'm really really rusty. Haven't really played with coco's in years. Loaned my good one out, never was returned. Was a coco3 w/ multipack and lots of goodies. ;_;
I'll help best I can though. Also if you end up needing other drives, I have some 720k 5.25s that will need to be cleaned and aligned but should work. Also have 2 external cases, and third which is a 3.5" in a tape backup hosing.What was said earlier, is somewhat true. Most pc drives will work. What the catch all is, is the address of the floppy drive. If I recall correctly , you have to set DS1/DS2/DS3 etc on the drives themselves. Most older floppy drives will have jumpers so no biggie. The only catch, is that the drive is configurable. Most modern floppy drives lack this option.
One last thing, coco2/3's require soldering a wire to provide 12v to 1 pin that as left off. This allowed backwards compatibility to coco1 packs. Super easy to do btw.
If I recall correctly, if you look at the motherboard top side, at the connector 1 pin is not soldered (pack connector on the right side, downwards towards middle of the board). Double check this, its been forever. But that should be the 12v pin which is unused. Find a 12v source on the board, and solder a wire to it and that pin. Problem solved. I suggest joining a CoCo forums to double check this mod information. Link I had is dead now (gimmechips). I'm 90% sure its right but like I said been years, at least 7.
Some may bash that controller, but IMHO its the best available for Coco's. Reason being, it requires little effort for using 3.5/5.25/8" drives. One I sold you is the exact controller I used to use on my CoCo3 years ago that i did the 12v mod to!
Read this, and you'll see whats required with luck to get other drives working on the other controllers!
http://www.doki-doki.net/~lamune/computers/coco/hd-floppy/
And last but not least, all radio shack coco stuff starts with 26-xxxx usually. So the first number would be a 2.
