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Bus Blaster JTAG debugger / Fried, then fixed
That fateful day I plugged the cable in backwards. I noticed that the CPLD was getting hot (and perhaps the FTDI chip too). I quickly unplugged the cable, but unfortunately the Bus Blaster was toast! I quickly ordered another JTAG pod to keep my work going until I could fix the BB.
I desoldered the CPLD from the BB using my trusty SparkFun Heaterizer XL-3000. When I plugged the BB into my computer, I was able to connect to the FT2232! So the FTDI chip seems fine.
Today I received a replacement CPLD (and a new 20-pin cable WITH a polarizing key) from Digi-Key. I soldered the new CPLD on my BB, compiled urJTAG from source, and loaded the JTAGKey buffer configuration into the CPLD. I tested my new (if slightly toasted) Bus Blaster on an ARM development board, and I was able to halt and reset the processor! Success!
Moral of the story: ALWAYS use cables with polarizing keys. I bought the H3DDH-2006G-ND, which includes both a polarizing key and strain relief. (Digi-Key shows this and similar cables as "Value Added Items," which means that they prepare these cables on-demand when ordered. Mine shipped the same day with the rest of my order.)
tl;dr
Use cables with polarizing keys. Cables without polarizing keys destroy your devices, time, and satisfaction.