Corshair RM750 - doesn't allow for board to turn on

[CapLeaker]

Pin 2 VDD is DC, not AC. Replace that starter cap on the VDD line (pin2).

[kotel studios]

Correct me if I'm wrong, but the starter cap should be in similar place to this guy in the typical application schematic, right? The one near the bridge rectifier is just to filter it. Or are we talking about the small SMD cap smoothing pin 2 to pin 1 (GND) on the PCB photo I posted?

[CapLeaker]

That cap in the picture.

[Agent24]

So I've measured the pin 2 of FSB127H and... the results are questionable...

Without mainboard:
PSU with mains applied - ~4VAC
PSU ON - ~5.3VAC

With mainboard:
Mainboard OFF - ~4.7VAC
Mainboard with shorted PWR_SW (still can't power it on) - ~60VAC

Now that 60VAC is very questionable. Max this chip can handle is 30V according to the datasheet. From what I could read from the typical application schematic, it also uses DC voltage and not AC (I made sure the MM is in the correct mode, in DC mode it spews -0.08V with spikes up to 20V when cutting mains power, AC mode has the results above).
What's even weirder for me is the fact that the PSU can boot without the mainboard with AC Vdd.

I made sure I soldered the probe wire to the Pin 2 and not Pin 7 (attached image is where the probe is soldered on).

Where's your ground reference? Make sure you're referenced to primary side ground (i.e. primary filter cap negative pin) and not output ground on the secondary side, or you WILL get weird readings.

[kotel studios]

Well, would ya look at that, bad startup cap! Was it well hidden tho, under a coil and a isolated wire.
Puffed up but not leaking. Hopefully it's the only issue (aside from ordering correct TO-220 FETs).

Rated 2200uF 16V, reads 1008uF
And as my luck would have it, no 16V 2200uF caps, only 1500 or 3300uF. Could also replace it for a poly, not sure if it makes sense to.

The B2050G diode is also fine.

And yup, I was measuring to sec. GND, not primary negative side.

[Agent24]

2200uF is pretty large for a startup cap, but if that is indeed the right one, it's very likely the source of all the problems.

[kotel studios]

Well, one side was connected to two pins of the 5vsb transformer, while the other to anode of that B2050G.

Maybe it's just another filter cap, either way it's more than out of spec which could cause the issues I had with 5VSB.

Found an used 2200uF 16v Ltec cap from a dead chieftec PSU. Seems to be inspec, so should be good enough for confirming if that's the only issue (which hopefully is the only one).