Looking for advice on how to correctly identify those tiny, glass, red/black diodes. Like these:

I have a couple small projects where I need a zener, I have several suspects but with no visible identifying marks I'm not sure if they are Zener or regular. (the first pic has ID marks.. ignore that the image is for physical reference only)
Advice?

 

Hello,

On the top I can read 48, that is likely an 1N4148.
Are there some prints on the other diode?

Bertus

 

Sorry @bertus I bet you snuck your reply in before I edited to add the disclaimer.

 

... and if it is a zener, just measure breakdown voltage.
all you need is resistor such as 10k, DMM and power supply (30V should do just fine).

 

Ah ok so just applying an increasing amount of voltage until it begins passing that voltage, yeah?

 

When forward biased, a zener looks like a regular diode.
You need to reverse bias the diode to determine the zener voltage. Use a series resistor to limit the test current.

 

You can test a number of semiconductor devices with an I-V curve tracer.

https://forum.allaboutcircuits.com/threads/diy-i-v-curve-tracer.184368/

 

for zener it is very simple,
supply voltage does not need to be adjustable, it can be fixed. you can use lower voltage like 12V but then you will only be able t otest zeners for less than 12V. so pick something high enough... 24V, 30V, 32V or so, and you can check 99% of zeners that you will come across

 

I have several suspects but with no visible identifying marks I'm not sure if they are Zener or regular.

Axial diodes should have sufficient space for identifying markings. Post some well-focused close-ups of the diodes in question.

I've sorted through thousands of loose diodes from the likes of Electronics Goldmine and have not come across any that weren't marked.

If they really don't have markings, you can reverse bias until they breakdown.

 

Thanks guys, here's two of them. Both were removed from old EDR Electronic S100 motor control boards. I did contact EDR last year but could not get component details.. nor a schematic.

 

here's two of them

Are you sure they're diodes? Have never seen any that didn't have the cathode marked.

I have some chip caps in axial packages that don't have any markings...

 

Test it on diode range on a DMM. Test in both directions and tell us the results.

 

Are you sure they're diodes? Have never seen any that didn't have the cathode marked.

I have some chip caps in axial packages that don't have any markings...

If they don’t have the cathode markings, they could be DIACs or similar trigger diodes. If the motor board had a Triac to regulate speed, then those are DIACs.

 

Invest a few bucks into one of the ubiquitous “component testers“ available from your favorite source of those sorts of things. My recommendation is this one (photo) or a variant, which is marketed under various brands—this one is a Longrunner. You can get them from Hiletgo on Amazon as well.

​

 

Invest a few bucks into one of the ubiquitous “component testers“ available from your favorite source of those sorts of things. My recommendation is this one (photo) or a variant, which is marketed under various brands—this one is a Longrunner. You can get them from Hiletgo on Amazon as well.

View attachment 325413
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I did not see this response until just now however I did actually order one of those. $14 for the one without a case..

 

Hello,

On the top I can read 48, that is likely an 1N4148.
Are there some prints on the other diode?

Bertus

On my power board of Panasonic DVD recorder DMR-EZ485V I suspect that a faulty zener diode does make the fuse to blow up immediately
Can you figure out what to replace this zener diode with?

 

Thanks guys, here's two of them. Both were removed from old EDR Electronic S100 motor control boards. I did contact EDR last year but could not get component details.. nor a schematic.View attachment 325387View attachment 325388

That will be a diac.
It will break over at about 32V in either direction, so as you increase the voltage to 32V when it gets to 32V it will suddenly start to draw current and the voltage across it will go to about 0.8V

 

which one to replace this zener diode?