Help indentifying a Diode

[fezder]

Hi, i'm repairing an PIR movement sensor module. Repairing started well, but i encountered these Diode looking components, they are easily described, they are in basic DO-xx packacke, same size as 1n4148, but they dont have any markings on them. I tested presumably working one with DMM, which showed ~0.5 forward voltage, none at reverse. The broken one gives SC.
other broken components are bzx 55c 24 zeners, 2pcs, bc 557 transistor, 220r resistors, 2pcs. and 2 pcs of these unknown diodes (?) see pic for reference

https://i49.tinypic.com/35kpjxi.jpg

 

[tronitech]

Without any markings or a schematic you're obviously not going to be able to identify them so I'd go with the 1N4148.

 

[kubeek]

You take the good one out and try measuring the reverse voltage. Or trace the board and someone can guess what they might be.

 

[KeepItSimpleStupid]

See if they ar ein a bridge configuration. The glass diodes look like 1N4148's. It's possible that they were replaced with the wrong part.

 

[fezder]

i havent replaced anything yet so far, DMM shows 1 as reverse voltage, so it could be 1n4148, or zener with high enought reverse voltage. the component is in paraller with bzx 55c 24 zener, backwards biased, if i look PCB correctly. i could try to draw schematic if it helps any bit?

 

[Grossel]

Hi.

I face the same problem as I have a dosen of similar diodes I've pilled of some old pcb's without any labeling that tell the part number.

Without any markings or a schematic you're obviously not going to be able to identify them so I'd go with the 1N4148.

I guess that means that the color combinations of small diodes has nothing to do with their part number.

 

[kubeek]

If you have an oscilloscope, a variac or a few diffferent transformers, using the famous octopus circuit you should be able to sort the lot into zeners and standard diodes.
Then if you got lots of one type, some destructive testing might tell you what current they are rated for.
If you really want, you can try measuring reverse recovery time and junction capacitance

 

[tronitech]

If you have an oscilloscope, a variac or a few diffferent transformers, using the famous octopus circuit you should be able to sort the lot into zeners and standard diodes.
Then if you got lots of one type, some destructive testing might tell you what current they are rated for.
If you really want, you can try measuring reverse recovery time and junction capacitance

Easier to just buy whatever diodes you need!

 

[Mr RB]

Unmarked 1N4148 are common in cheap Asian made stuff, it's the worlds most common diode and they save $$ by not printing on the diode.

An easy test is to put compare mystery diode with a real 1N4148 using a 1k series resistor and attach your 12v PSU. If the two diodes measure roughly the same voltage forward, and both measure 12v reverse, then it's highly likely both are 1N4148 diodes.