I've got a faulty GTX 1070 Graphics card here with a blown SOT-23 casing IC. Looking at it you can se N51 and looking around on the board I can find another component like it with N51K.

I cannot however figure out what the component is? It looks like a transistor of sorts.

Any ideas?

Blown SMD IC

Exactly similar IC

Larger area

enter image description here


Thanks for your help so far.

  1. I don't know why it failed, I purchased the card on a whim in the hope I might be able to repair it. Probing around the rest of the circuit I see no reason why it shouldn't work other than this, there are no other shorts.

  2. Please see attached for an expanded area of the circuit.

  3. I've probed the existing N51K IC and as you look at the picture: Right pin to left 1.5v forward, centre to left 1.5v forward so it would ring true as being some kind of transistor, left pin being the gate. Does fit the theory of it being a Si2305CDS as it matches the pinout and it being PNP

  4. The center pin on the blown IC goes to the 100ohm resistor and that goes to pin 3 on the ON 702 IC. Having done a bit of searching it seems at first look that the 702 IC is a dual N-Channel mosfet 2N7002DW however probing it doesn't fit as pin 5 probes to pin 1, so either that's a short that shouldn't happen or not the correct IC.

I'll have a further probe around and see what else I can find.

  • 1
    \$\begingroup\$ Do you know why it failed? If not, usually the component that went pop is the weak link in a chain of failures, so replacing it may not fix the problem. \$\endgroup\$ Commented Jun 6, 2020 at 13:13
  • 1
    \$\begingroup\$ Also, do you have a rough overview of the surrounding circuit - i.e. can you tell what other components the pins connected to. \$\endgroup\$ Commented Jun 6, 2020 at 13:32

1 Answer 1


Couple of options, the first second being most likely of the two.

  1. ZXTN5551FL - 160V, SOT23, NPN High voltage transistor

    This has package marking N51, though I can't find any photos of it to find out whether it appears along with the letter K. The manufacturer (Diodes Inc.) do use 1-character shortened date codes on small packages, in which case K would mean October 2015 (when did you buy the card?). However given its a part originally made by Zetex rather than Diodes Inc, I'm not sure if the date codes apply.

  1. SI2305CDS - P-Channel 8 V (D-S) MOSFET

    This has a package marking of N5, but from pictures of such devices, the marking appears in front of additional characters which represent date code information. However the package marking on your part doesn't match the lettering style from other photos of this part, and is missing a small overlined character in the middle of the number.

    Having said that, there is a similar thread on another forum which is looking for a similar part with number N51Y in a very similar style to your parts, which apparently they were able to confirm from the manufacturer was a SI2305CDS, which leads me to suspect your parts are too.

    A P-Ch MOSFET also makes more sense based on your first picture as it looks to be related to switching of a power rail

  • \$\begingroup\$ I've ordered some SI2305CDS chips, also been probing around the area. Switched the GPU on for the first time and there's no GPU or Memory voltage so I suspect that this faulty component has something to do with the enabling of those circuits. I'm putting together a crude drawing of the circuit as I probe it as it's easier than trying to remember what goes where! Even if there's no more answers to this post, I'll still have a record of it. \$\endgroup\$
    – Dazmatic
    Commented Jun 7, 2020 at 7:59

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