How to Test & Read Unmarked Rectifier Diodes: Parameters & Function Explained

I know that everyone should know but how do rectifier diodes work? I see! How to read its parameters if nothing is written on it? Thanks in advance for your help!

Preferably a digital meter. You set it to a range marked with a diode symbol or something like a sign that means sound. Plus of the meter to the anode, minus to the cathode (strip on the diode), you should display a value (somewhere 600-700), this value means the voltage that must be given to the diode in order to conduct it (of course in mV ). When you connect the diode in the reverse direction, you should see 1, i.e. infinity (in the reverse direction, the diode cannot conduct, unless you hit a few kV, the force of things will start to conduct it, and it can even shine) )
Generally, you can do the same with an ohmmeter, but you need to give a range preferably over 1kOhm ....
If the diode does not write anything, then, in general, nothing but what you can check with the meter, you will not find out ... well, unless you determine the size of the current
You can still check the diode, the battery and the bulb , you turn it on in series with the bulb and connect it to the battery , in the direction of conduction, the bulb should glow and vice versa, it should not
8)

Ehhh ... so: assuming that this is, as you say, a rectifying diode, the parameters "roughly read" by its dimensions - power. Unfortunately, this does not tell you much about the material it is made of (germanium, silicon), and thus about the voltage drop that is generated on it during conduction. You can check it by including in a simple circuit - in series with eg "proverbial bulb" and to the battery. If you add a bulb to the plus, and the diode behind it, with the stripe pointing to the minus, then the bulb should light up (it may turn out that you have insufficient voltage, e.g. 1 finger 1.5V is definitely not enough), then it works in a conduction state. If you say so, reverse its polarity and it should now be blocked and non-conducting. The bulb will of course not light up. If you want to know more about it, please read on, keywords: diode, rectifier, Graetz circuit, PN junction, electrons, holes; P transition characteristics of a diode. You'll find everything in every electronics book.

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Sorry I did it again, but the interval between posts is seconds

Thanks! But if it biases the diode in the forward direction and the meter beeps and displays a value of about -500, the diode is out of order? I once heard that the meter has no right to squeak on any semiconductor! Is it true?

True An efficient diode will not cause the meter to squeak, which signals a short circuit regardless of the direction in which you connect it
And this meter shows you 500 or 50.0? because something does not suit me here ...

If the meter shows -500 (minus), unsolder at least one end of this diode from the circuit, because it looks like some capacitor "bothers" you

And the material from which the diode is made you can also estimate with a meter (this is what Vinnie said) - germanium and Schotky diodes about 0.2V (but who makes germanium diodes now?)

fact ..... probably no one makes these diodes anymore ... but there are systems in which a drop in the conduction direction from 0.2V is irreplaceable by a silicon diode ... e.g. some detectors ....

And if my ITT diode shows 0 on both sides, while in the next 2 9I9 diodes the value is about 400, but also on both sides, what does it mean ?? All to be replaced ??

So if such a diode conducts in both directions it is to be replaced? Did I understand that correctly?

Hello. I have the impression that you are checking the diodes without disconnecting even one end, and this is a mistake if you have no experience. Be sure to disconnect one end of each LED and then check it in both directions. A screeching meter is generally associated with low resistance, but the level of resistance at which it occurs is inconclusive, so it is not an absolute indication of the condition of the diode. The meter must not squeal in the obstructive direction - it should be "infinity". Greetings.

Hi,

I am wondering about the efficiency of one of the diodes. According to the method of checking described here, this diode in both directions shows values of about 560-570. 5 other, identical diodes that I found, show a value of about 600 in one direction, and just 1 in the other (I checked all of them on the board, without moving them). Does this mean that this one is faulty and should be replaced? If so, I probably won't be able to do it myself because it's too small for a regular soldering iron. I don't even know how to read the values off it, the markings are microscopic.... - Something like 32 at the top of the black bar, or looking from the other side it could be "2C"....

Use a magnifying glass to read the markings. And as for checking, read #10, so far you can tell there is no short circuit.

_jta_ wrote:

For now, it can be concluded that there is no short circuit.

Is it functional or not ?

Unknown. After all, you haven't checked that the meter current flows through this diode.

But doesn't the fact that all the other, identical diodes, also measured on the board, show the "correct" values, i.e. ~600 one way and 1 the other way, and only the one in both directions ~600, mean that something is wrong with it? And that maybe, after all, such a measurement, although taken not quite according to the art, tells us something there?

No, it doesn't mean anything - it could be coming from other components. By what do you want to distinguish whether it's a fault or an element on the board?

This measurement says something: that this diode is not shorted. But a shorted signal would no longer mean that it is the diode that is shorted.... On the other hand, a "1 " both ways (distinguish from " 1") would mean that the diode has a break, not necessarily inside - maybe its leg has soldered off, or the tin has corroded and the end of the meter is not contacting.

In that case, I wonder how the author of the original thesis of my case supposedly concluded that his diode was dead, e.g. shorted.... A diode does not have to have visible mechanical damage to fail to function properly, and there are dozens, if not hundreds, of them on the board.... Because the whole issue of just this diode comes from the 1st post in this thread https://a4-klub.pl/topic/39884-licznik-w-a4-b5-i-jego-naprawa/ . After all, the author didn't pick this diode at random, nor did he solder them all out one by one to check them.

Because if my measurements, which supposedly show nothing certain, are meaningless, and the colleague from the original thread, if the diode was not visually damaged (and the description does not suggest this, even indicates internal damage), also could not diagnose it in this way, then trying to replace this diode misses the point, because it could just as well be another component of the whole indicator (most often the motor falls down).

I'm getting to the point that since it's unfounded to even suggest that it could be just this diode, it's a pity for me to spend almost 100 PLN to have an electronics technician replace it, because there's little chance that it will change anything....

On the other hand, assuming that the author of the original thread could have checked the diodes on the board though (because it would be difficult and I can't imagine that he soldered hundreds of them to discover the cause of the problem) and just picked this one out on the basis of the other values returned (just like with me), then I might be tempted to have it replaced and pay for it. But any way of measuring it must show that there is a chance of it being faulty....

Perhaps, based on the diagram, he ruled out that the detected short circuit was from something other than the diode?

I think he didn't have a schematic or he would have mentioned it in the post. And I think by that he simply checked on the board. Only unfortunately there is no specifics there and no information about what the measurement showed and what diode it is.

As I have to replace the clocks anyway, I will try to desolder this diode and check it. I would not solder a new one with a regular soldering iron anymore.

If the reason for 'conducting' both ways is the resistor, then all it takes is a slightly higher current, and some of that current will flow through the diode one way and not the other - an indication that the diode is functional. But for this you need to understand what you are measuring and how you are measuring it.

So if I solder out the diode, am I able to check it in the same way as I have done so far, with a normal meter set "to diode"?

If you know how to use a meter as such, then yes.

Aha: you can't rule out the possibility that these are two diodes oppositely connected in one housing - this combination has long been used to reduce crackle, so maybe they make special diodes. The best thing to do would be to read the designation and find the datasheet note, but for SMD components this is not so easy.

I have just soldered out the diode.

Testing it with a "normal" meter set to the diode mark, the diode shows "1" one way and ~570 the other.

Does this mean that the diode is fully functional?

Correct. The question is what the meter will show for the plate at the diode location.

_jta_ wrote:

what the meter shows for the board in place of the diode.

Both ways ~570. And this is the value it shows by connecting the different pyncts on the board between the different components, also in both directions.

I assume, however, that the motor of one of the clocks is faulty and it will be easier for me to replace the whole set....

It could simply be a resistor - maybe it just happened to be one.

I can't think of anything else here, and a possible repair at an electronics technician would certainly be more expensive than buying whole clocks used. Well, nothing, diode eliminated, no more turning my head in this thread. Thank you for your help! .