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I have a burned diode with no markings, can someone help me identify it? Answered

I checked the resistance with multimeter and it gives me 130 ohms both side and I checked it with diode checker and gives me 0.065 v on both side.


This might seem like a dumb question, but regarding the tests with the multimeter, were these done with the diode still attached to the rest of the circuit?

Picture 4 shows this diode maybe wired to two sides of that relay. 

I am guessing that this is an ordinary silicon diode (e.g. ln4148), and that is wired in parallel with a relay coil, for the purpose of absorbing  the current in the relay coil when this is turned off suddenly.

If you put an ohmmeter across such a diode while it is still connected to the circuit, all you'll measure is the resistance of the relay coil, and 130 ohms sounds like a believable number for this.

Yes it was in circuit  I took it off and it measure 0.650 ohms and 0.475 v oneway. Thanks

Glad I could help somewhat.  Hope you get this alarm whatchmacallit, whatever this thing is,  fixed, or if you don't succeed in fixing it, I hope you find some entertainment, and/or enlightenment, in the process of taking it apart.

Any idea what its for ? It LOOK like a boring LL4148, but it might be a Zener.


yes it does look like LL4148 Fast Switching Diode

How about a photo of the whole board ?

What's it in?

If you can find a schematic, that should at least tell you what general kind of diode it is -- ordinary versus zener vesus whatever.

Odds are pretty good that you can replace it with any diode which can handle the current and have the circuit at least limp along. The exact details of switching speed and transfer curve do matter in some circuits, but in many they don't.

The more important question is: What caused it to fry in the first place? Until you resolve and fix that, there isn't must point in installing a new diode and frying that one.

It's in a wireless home alarm system.  The system fell from the wall, and the dc adaptor supply jack broke and caused the system to malfunction.

(Should have said "current and voltage", but I'm guessing that a surface-mount device doesn't have a lot of either running through it.)