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SMD part identification

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Darius Baronas

Member level 3
Nov 15, 2014
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Hi. Can't recognize part...It looks like diode, but it is white and without any marking on in...what is that part ? Please help, thanks.


white smd - usually it is a fuse but could be something else as well.

No visible mark at topside of the component.
It was certainly welded inverted.

So you thing there should be marking on bottom side ?

Many small SMD components don't have markings. I won't expect a bottom side marking. Upside-down mounting is effectively impossible in automated pick-and-place assembly.

I would narrow down the range of possible components by in-circuit measurements and tracing of circuit function.

Could be a diode, I have seen a few white bodied switching diodes with a black band to mark the cathode, it should be fairly straight forward to check with a DMM.

I think it is not a diode. I have seen a few capacitors in white color but the mark makes me wonder about that suggestion. Check with the multimeter to come for some final conclusion and report us to know about this.

With continuity test there are short from bouth sides, resistance from bouth sides is 0,03 Ohm, and no capacitance. So maybe this is fuse ? If yes, then how to know rated current and why there are marking like diode on it ?

The part position doesn't look like a reasonable place for a fuse. I would expect a RF chip inductor in this case of a low R component. Some have asymmetrical markings. Unfortunately no chance to see the value.

And one more, on SMD transistor-like part there is marking "NOt" . I guess that is TN0200T N mosfet or BFR505T NPN transistor. But how to know exactly ?

I didn't study the markings but would opt for the GHz BJT as a first guess. Distinguishing between a MOSFET and a BJT is quite easy with a multimeter.

I think that is BFR505T NPN.
ID Code Variations
Many manufacturers use an extra letter as their own identification code. If the device is from Philips it will
sometimes have a lower case 'p' (or sometimes 't') added to the code; Siemens devices usually have a lower
case 's'.

Hm... but here we can to measure inductance of that part ?

1.0 nH - 470 nH ?

**broken link removed**
Hi again. Problems with transistor, mentioned in #11 post... i think it is not TN0200T, because i tested it with multimeter. I i do not know or it is BFR505T, because i measured all posible combinations, and got very strange table. Please look at it and help me identify that part, thanks !


  • part_unknown.PNG
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I hope you unsolder this transistor before test. Set multimeter in diode/buzzer mode and repeat test.

I hope you unsolder this transistor before test.
Yeah, the findings are a bit unclear. I presumed a continuity test so far.

Does "0" mean open circuit (e.g. > 2V)? If it actually means zero (unlikely, I think), you should report the respective ohms reading.

The reading is in diode mode, so 0 means 0 voltage drop i think. I have two same transistors, one still on board, other is desoldered. Measured bouth and result is same. After work will measure all resistances between pins and post here.

This is datasheet for BFR505T. **broken link removed**

Maybe inside them is something interesting, more than in ordinary NPN transistor ?
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What is the component unsoldered near?

You can see what is around that transistor in #1 post . There are resistors, capacitors, one small inductor and 433Mhz xtal. Xtal output goes straight to the transistor pin 1, so pin 1 should be base i think. And depending on xtal high frequency, so maybe this is BFR505T, which is high frequency npn transistor. But why multimeter readings is so strange then..

Look at this.
**broken link removed**
**broken link removed**

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