IC identification

[MichR]

Hi everyone
I have got a Seasonic X 850W PSU which refuses to turn on: 5VSB goes to 0 and PWR_GOOD is always at 0V; all lines (+12V, +3.3V) are at 0V and the relay does not switch.
After a lot of struggle I found out a shorted IC with refdes "U4". After having desoldered it, 5VSB remain stable even after shorting PS_ON line but still does not turn on (all lines are at 0V and relay still does not switch)
Can someone help me identifying this IC?

It's a SOT-23 with marking "5014T". The same IC is used on another part of the board (with refdes "U3"). I made some measurements and it seems to be a dual diode, but I want to be completely sure before replacing it.

Also, I found out that many power supplies use it, and it is sometimes replaced with a 0 ohm resistor. I tried it and the relay switches, but +12V line (and perhaps +3.3V too) goes down to 0 in several seconds.

Thanks

[MichR]

I found out Cooler Master V1000 uses the same Seasonic KM3 platform (so PCB is essentially the same). I could obtain high res pictures on the web and it seems the IC with marking "M3|L" or "M3IL" is an equivalent. This may be helpful to identify the component.

[amyk]

501yw is SPN5001.

[Cliff Matthews]

Out of curiosity.. (I'm older & not up on newer PSU's) does the relay bypass a thermistor once input capacitors are charged?

[MichR]

501yw is SPN5001.

Thank you. I'll see if I have an equivalent one and I will try it out.

Out of curiosity.. (I'm older & not up on newer PSU's) does the relay bypass a thermistor once input capacitors are charged?

Yes, as far as I know.

[amyk]

I recommend tracing out the schematic at least in the vicinity of the part, to see if it makes sense --- there are often very different parts with the same marking and package, especially SMD where the markspace is small.

[MichR]

I recommend tracing out the schematic at least in the vicinity of the part, to see if it makes sense --- there are often very different parts with the same marking and package, especially SMD where the markspace is small.

I think it does. For instance gate of U4 is connected with the gate of U3, so the line controls both the MOSFETs. Also, both drains are connected to a high voltage line (400 V maximum) with three resistors in series (about 6 M ohm in total); this might explain the high VDS(max) of the transistor.

Since I cannot find this component available at a reliable source, I'm going to contact the company and request some samples. In the meanwhile, may I ask you to identify the other component, the one with "M3..(something)" as marking? This can confirm it is actually a transistor and perhaps it may be easier to find from a reseller.

[MichR]

I finally fixed the power supply by replacing this mosfet.
I could not find the same model of the mosfet, so I started looking for an equivalent.
At first I tried to order some AO3162, but the (chinese) seller sold me unknown sot-23 components with marking "UBA01". I kindly asked him which kind of component sold me, but never received a response  . Got a full refund.
At last, since I didn't want to wait another couple of months for another garbage I ordered some BSS127 from ebay. I replaced U4 and U3 (the two SPN5001 mosfets) on the PSU with these BSS127 and it started working again.