so i have a broken chumby classic (ironforge 1.8: http://files.blueocty.com/hdwedocs/IRONFORGE_MX21_V1_8_FINAL.pdf ). in some sort of fashion, there was a short in a power rail somewhere (i suspect DC in and ground, but i'm not sure if so, or if that was indeed the root cause) which blew a diode and some buck regulators. i have now replaced all those parts and checked that all voltages (5v, 3v3, 1v8) are correct and the unit does power on however never functions beyond a white screen
spitballing appreciated 
@mavica_again our first thought involves JTAG'ing the CPU to see if it's fetching instructions
@atax1a from my limited knowledge using swd, what would i see without an attached debug source code? just registers changing? how would i tell what's working?
@mavica_again stepi disassembles the next instruction when you issue it, and if it looks like it's fetching code then you've got a good CPU and a good ROM. you could also poke bytes into memory and try and read them back, if you know where that's mapped
@mavica_again the way it works on our cortex m0 with SWD is that we use
openocdwhich detects the chip and serves a GDB remote from which you could, e.g.,stepia few times to watch it execute