It appears that buck regulator #2 is not being turned on. One of the other regulators (L3) is enabled but has no output or an output which is too low, so it is either faulty or overloaded.
This is my guess for the power distribution:
Code:
DC-DC converters Main ICs
.--------------. .-------------.
R72 | | | |
+5V ___ Vin | U20 | | NAND |
o--+---|___|--+-->| | | |
| 10R | | U19 |--->| SDRAM |
| | | | | |
+----+^+---' | U17 | | Controller |
| ||| | | | |
.-. === U15 | | | |
| | | | | | |
| | | | | | PSU |
'-' | | ENable | | control |
| | '--------------' '-------------'
'------+ ^ | |
| | | |
___ |/ '----------------' |
.--|___|--| Q4 |
| |> |
| | |
| | |
| === |
| GND <-- PSU-ON |
'--------------------------------------------'
AISI, the SSD is stuck in soft-start mode. All the current for the SSD passes through R72. Applying Ohm's Law, we calculate the current draw as 0.34A.
I = V / R = (5V - 1.6V) / 10 ohms = 0.34 amp
To switch from soft-start mode to full-on run mode, a PSU-ON signal must come from somewhere. Also, two of the DC-DC converters need an ENable signal, possibly from the same source. I expect that this source is a small "PSU control" section within the flash controller. U19 is a 2.5V LDO linear regulator, so perhaps it provides the enable signal for buck regulator #1.
I think I would need to determine the sources of the ENable signals and the PSU-ON signal before I could begin to properly understand this circuit. I confess I am stuck at this point.