It is a diode but no marking at all, except the cathode band. Please help.

unknown diodes in the upper left corner

  • \$\begingroup\$ I'm not sure we can identify that. Why do you need to know what it is, do you need to replace it? Knowing why you need it will help guide people to give better answers. \$\endgroup\$ – Hearth Apr 5 at 12:39
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    \$\begingroup\$ I'm voting to close this question as off-topic because there's no option for success here – an unmarked component without a schematic. \$\endgroup\$ – Marcus Müller Apr 5 at 13:33
  • \$\begingroup\$ Well that's the whole point that it's unmarked, otherwise I wouldn't post it. My only chance is that someone used such a component. It shouldn't be something completely obscure. \$\endgroup\$ – Cubrilo Apr 5 at 13:36
  • \$\begingroup\$ Have you tried googling diode without markings except for a white band? Maybe it isn't a diode too. \$\endgroup\$ – Andy aka Apr 5 at 15:03
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    \$\begingroup\$ Have you measured the package to identify size and gone through digikey for same case size? Have you done a diode test with multi-meter? Are you trying to replace a faulty component or need this for some other reasons? More infor you give more chance of success. \$\endgroup\$ – EasyOhm Apr 6 at 1:56

It appears to be an 0805 case (you can confirm with a ruler). If I look at current Digikey offerings there are only Schottky 1A diodes in that package, however the package is not the same (has castellated ends).

I can, however, find offshore 1N4148 equivalent with an identical looking package so that might be a good guess.

enter image description here

You can desolder it and measure the Vf at some reasonable current, and thus rule out Schottky diodes. You may be able to measure the capacitance which will rule out many rectifier type diodes.

The inexpensive Chinese LCR component measuring devices show 3pF on a regular 1N4148 and Vf = 691mV. Schottky diodes will measure much less Vf and rectifiers will generally measure much more than 3pF capacitance.

Of course it could be something else like a varicap diode, if you know something about the circuit you may be able to figure it out.

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  • \$\begingroup\$ Thank you very much, somehow I forgot to search by package (case). I found TS4148 RYG (Taiwan Semiconductor) and CD4148WS (DC Components), there are probably more manufacturers, so it's pretty standard component. \$\endgroup\$ – Cubrilo Apr 8 at 9:15

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