Ydee wrote on 2021-05-17, 13:19:
...but I notice that the D1703L looks like it's been resoldered/replaced before. Soldering the large plate on the back can be a problem,...
I don´t think, that this FET was resoldered - if You're thinking about that area (solder pads), probably was planned largest (TO-220 pack) FET to use, I think. Now is DPACK size.
Ok, I thought the soldering didn't look as neat as the other pads, but it's probably just that the pads are oversized.
U13, IT8282M... Could you check what the voltages are on those pins, particularly pin 7 which should be the Power Good signal from the PSU, and should be 5V.
Of course I can, everything, what You need. Look at the photo (click to zoom in).
Great, thanks. So reading that datasheet I posted last, it looks like the power sequence is:
SB_PSON# (input to pin 5) triggers ATX_PSON (pin 9 output to PSU), which turns on the PSU. Once its voltages are all correct, it signals ATX_PWRGD back to this chip (pin 7). This chip then turns on other regulators, one at a time, and stops if any of the voltages are wrong. Only when all the voltages are correct does it release the CPU_PWRGD line (pin 11) and the computer can finally start to boot.
Also from the datasheet, it looks like Vdimm is the first board level regulator that the power sequencer tries to turn on.
Pin 13-15 are the output enable lines for Vdd (cpu core voltage), Vdda and Vldt (other cpu voltages, I think clock and bus termination), and you've measured those all enables as around 0V, so they're all turned off, which you can see because the input sense lines (Pins 1-3) are all around 0. Pin 12 is the Vdimm output enable, so that should be turned on, but the input to Pin 4 (the Vdimm sense pin) is only 1.13V.
So we've got confirmation that there's a problem with the Vdimm voltage, and an explanation why the CPU voltage is missing: the power sequencer keeps it turned off until everything else (including Vdimm) is right.
That means we can now start tracing forward from there, and it's likely once we fix the Vdimm problem, the other voltages will then come up correctly. Two things that would be really useful to find at this point are where pins 4 and 12 connect to, which will need your metre in ohms mode (I'd suggest the 2000 ohm range) and the board unplugged. You're looking for anything that measures close to 0 ohms between pin 4 and something else, and then pin 12 and something else. Give the meter a second on each point to see if it gets a reading or not.
If you can find one of the FETs connected to pin 4, then that's the FET that should be supplying Vdimm, probably best to start testing on those FETs near the RAM slots. Put either probe on pin 4, then start touching pins and tabs of other components with the other probe.
It might be more tricky to find where pin 12 goes to, but I'd start probing around that AS324 by the CPU12V connector. This measurement
one will tell us what should be controlling the Vdimm regulation. If we can keep tracing these forward and backward then eventually we find what's failed.