Problem identifying a transistor

[MRKSXC]

Hello.

I can't for the life of me figure out what kind of transistors Im dealing with.

Top markings are ND2K with 2K underlined and the other one NDL1 with 1 underlined. There are no marks on the bottom of the transistor.
Package should be SOT-23-3, Or SC-59
They are both part of a 4G/5G router power supply, ND2K being on the 4G router and the other on 5G, but the power circuits are identical.
Marking on the PCB next to them is Q1.

I spent the last day on google and found SOT-23-3 and SC-59 packaged transistors that have the ND top mark, but nothing with 2K or L1.

[Jwillis]

The dimensions are important to narrow down the search. Sot23, SC59 and also Sanyo Electric SSFP package.
Try these sites as there are several possibilities. https://smd.yooneed.one/code4e44.html  and https://english.electronica-pt.com/smd?ref=ND&opt=s&page=2
The second set of letter and number (L1 and K2) could very well been date codes.

[MRKSXC]

Yeah thats what i thought, 2K and L1 probably are date/lot codes, but on most of the transistors with ND marking the date code is turned sideways not like on mine.

I measured the ND2K one and its 2.95mm x 1.55-1.60mm x 1.09mm (measured with calipers)

[Jwillis]

Best bet would be the BF 841 https://pdf.datasheetcatalog.com/datasheet/infineon/1-bf840.pdf

[MRKSXC]

Well, BF841 are hard to find but after a lot of searching i found a few on aliexpress, But just for good measure i got some BF840 as well from a local supplier.
The specs are mostly identical so i hope it will work.
I also got a few 50C02CH-TL-E which is has higher Pc, Vce, Vcb, Veb and Hfe, but the frequency is 500mhz, BF840 and 841 are 380mhz, so would that be an issue ?

[Jwillis]

Well, BF841 are hard to find but after a lot of searching i found a few on aliexpress, But just for good measure i got some BF840 as well from a local supplier.
The specs are mostly identical so i hope it will work.
I also got a few 50C02CH-TL-E which is has higher Pc, Vce, Vcb, Veb and Hfe, but the frequency is 500mhz, BF840 and 841 are 380mhz, so would that be an issue ?

I say best bet would be the BF841. But it also depends requirements. There are several transistors that use that marking code. Check out https://www.keccorp.com/kr/product/product_view.asp?idx=56 and https://alltransistors.com/adv/pdfview.php?doc=2sc2412kgp.pdf&dire=_chenmko

There are others in the listing of the websites posted.

Transition frequency (f_t) basically signifies the absolute operating frequency limit. As the frequency of the signal input applied to the base approaches the operating frequency, the hFE begins to reduce. When hFE becomes 1, the operating frequency  (f_t) is referred to as the gain bandwidth. Operating frequency can be anywhere around 1/5 to 1/10 the Transition frequency (f_t)

[MRKSXC]

Update, The BF840 or the other one i ordered did not work.

But I did find a working device and desolder the piece from it and using my old, cheap and dusty component tester it showed this...
Gate and Source (Pin 1 and 3) are swapped because i forgot to flip it when plugging it in the tester,
So when looking the transistor from the top, counting from the bottom, left to right the two pins are Gate and Source and the top single pin is Drain like on the schematic i drew.

[Jwillis]

Update, The BF840 or the other one i ordered did not work.

But I did find a working device and desolder the piece from it and using my old, cheap and dusty component tester it showed this...
Gate and Source (Pin 1 and 3) are swapped because i forgot to flip it when plugging it in the tester,
So when looking the transistor from the top, counting from the bottom, left to right the two pins are Gate and Source and the top single pin is Drain like on the schematic i drew.

Oh awesome! Glad you got it. Definitely a tough one to figure out. With those parameters, hopefully you can find replacements.

[MRKSXC]

I gotta be honest, I have no idea how to search for a replacement based on that info and i have not found any mosfets that have ND markings that are SOT-23, SC59 or TO236 package.
Can I just get a SOT23 mosfet that I would think would be strong enough for it or is there something i should look out for? (I know how to swap stuff, Not so much how to find stuff without having all the numbers in front of me )

[Jwillis]

Getting the exact component is probably not crucial. In power applications transistors (BJT or MOSFET) can be replaced with near equivalents much easier than other applications. You have some parameters you can work with. If you can figure out the voltage to the drain then finding a replacement will be easier. A mosfet with a RDSon of around 200mΩ, Gate Threshold voltage  VGS(th) of around 2V and the Vds can be fairly high above actual operating voltage.

[Jwillis]

What is really annoying is some component manufacturers don't put the marking code in the datasheets. Can never understand what the darn secret is.

[MRKSXC]

What is really annoying is some component manufacturers don't put the marking code in the datasheets. Can never understand what the darn secret is.

Yeah I feel that, Why are there no marking codes in datasheets.
I've never had so much trouble finding out parts with any device other than this, Its Zyxel NR7101 and LTE7480 routers, They both have the same POE transformer, It has a marking, Google it, it does not exist, How about another 2 mosfets I needed, google the markings, Nope, no info, I had to Dwell deep into some russian forum, Heavy use of google translate, find out where someone asked about the same component, and luckily someone had an answer. Aaand now the darn small ND mosfets.... No hits.

I did order some but i have no idea if they would work or not. BXT1000N06M and SI2308BDS. with the limited info i had alltransistors.com gave the SI2308 as an option, BXT1000N06M I got because i hope i get lucky and it would work, No science behind it.

That mosfet is right after the transformer, (should be the 48 - 12v one) Transformer itself has 5 pins on the 48v side with 4 actually connected and 5 on the other side with also 4 connected, 2 pads are connected together, One is connected to ground and one is connected to some small diode and cap. since i have the mosfet removed i checked the pads, Drain is connected to some capacitors and a diode, Gate is connected to one pad coming from the transformer and source is connected to the double pads that i thing is the 12v one because injectin 12v on those pads starts the router. No ground connection on any of the 3 mosfet pads

[MRKSXC]

Good news, I have fixed it finally.
BXT1000N06M did work and the devices seem to work like they used to.

Thanks Jwillis for the help.

[bostonman]

I have come across components without markings many times. One thing that helps is measuring/tracing the circuits.

This way you know the working voltage(s), the resistors, and you can at least get an idea of current values you're dealing with. Even if you can't find the exact component, you can (hopefully) find a replacement that's equal or more robust.

Also, which meter was that you used? Did it automatically tell you the device type?

[MRKSXC]

I have come across components without markings many times. One thing that helps is measuring/tracing the circuits.

This way you know the working voltage(s), the resistors, and you can at least get an idea of current values you're dealing with. Even if you can't find the exact component, you can (hopefully) find a replacement that's equal or more robust.

Also, which meter was that you used? Did it automatically tell you the device type?

Well, I totally forgot to measure the voltage when the mosfet was desolderd. I did try to measure it when it was on the board, but it didn't show anything, probably because it was shorted and everything was getting hot so I ditched that idea early on.

The meter I used is a chinese DIY kit i got a few years back that you had to solder together yourself, but It does automatically tells you the device type and so far it has been pretty accurate. It sadly gives little other information thou.
Since i got it a few years ago, I dont remember the name, but the closest thing i found is the GM328A tester, Or any other Transistor tester on Aliexpress (inside they are probably the same)

[gamalot]

https://datasheet.lcsc.com/lcsc/1811021215_APEC-Advanced-Power-Elec-AP2310GN-HF_C46746.pdf

[Jwillis]

Great work! Glad you got it working!  And it looks like gamalot found an exact match as well.
The  GM328A tesyer is a very common early model that uses the Atmega 328  8-bit micro-controller.