Hey there!
I've got a Discovery (version 1, rev.C) that does absolutely nothing when plugged into the computer. The computer makes no sign that it was pllugged in at all. After some debugging and tracing out power supplies with help from the schematics in the reference guide and other solutions posted on this forum, I've been able to narrow the problem down. Current consumption for the whole device is under about 5mA (measured with a USB power meter). The ferrite beads on the USB power lines are both good, as is the protection diode.
Probing all the power supplies reveals that all contollable enable lines for power supplies are off (including the one for IC20). This means the AVCC5V0 line is off with all the subsequent analog power supplies, as well as the 1.8v digital supply. I assume this is because they are only enabled after the FPGA has been configured. The 1v and 3.3v digital supplies are operational.
Probing the FTDI chip reveals that it is properly powered and all looks normal except for two things. VCORE on pin 38 is 1.8v as it should be, but VCCA on pin 37 is grounded. In addition, PWRSAV# on pin 31 is grounded, forcing the chip into suspend mode (which could be why VCCA is low?).
I could not find anything besides the FPGA that might be able to suspend the FTDI, so I am left with the conclusion that one of these two chips is damaged.
Since I don't know much about FPGAs and I don't have a board layout to consult, this is as far as I can easily get without replacing chips. What are your thoughts or suggestions? What is the FTDI power save line connected to?
Thanks!