Cool, thanks for the replies.
So with the hacked cartridge with an SD card installed, the JB should just boot into its default demo videos, ignoring the SD card? Since my JB actually halts with a blank screen, I guess I may have a problem.
The only etch cut I'm concerned about is the long one next to the resistor (R2 to ground), so I will verify that it is indeed cut all the way. Also, when I soldered across the two resistors R2 and R3, I accidently desoldered R3. I thought I soldered it back in place, but I will recheck that as well.
Thanks again for the help!