Diode - SMD code - Marking code

ted060411 · Joined: 12 Apr 2006 Posts: 2

Hi all,

I need to identify an diode (glass case, through hole device) with marking number: 2 18 (first row: 2; second row: 1 Cool

. Can anyone help/show me where to find its datasheet and its specification?

torbjorn · Joined: 07 Jun 2007 Posts: 370 Location: Sweden

Usually, it is difficult to identify small hole mounted diodes with a such simple marking code.
But you can be pretty sure that it is either a silicon switching diode like 1N4148, or a schottky diode, or a 0,5 W zener diode.

A good way of identifying it can be to study the circuitry around the diode to figure out which kind of diode should fit in there.
Another way, if we assume that this particular diode is faulty, is to look for another diode with the same marking in the equipment, de-solder it and take some measurements.
By using the diode tester function of a DMM, you can easily tell if it is a silicon diode (forward voltage drop of 0,55 - 0,75 V) or a schottky diode (forward voltage drop well below 0,5 V).
In case of a silicon diode, check out if it is a zener by connecting it in reverse direction (+ to the cathode) to a lab power supply via a resistor of, say 10 kohm, then slowly increasing the voltage from the power supply while watching the voltage drop across the resistor. If you get a considerable voltage drop, equalling a current in the order of 1 mA, at a moderate voltage from the power supply, then it is a zener. Then you can check the voltage across the diode at, for example, 1 mA and 5 mA through it to determine the zener voltage.

frantal · Joined: 05 Jun 2011 Posts: 5

I am repairing a 220VAC/5VDC power supply for a router. I am looking for to identify a through-hole diode with marking code 2 18 (printed in two rows: first row 2, second row 1 Cool

that I marked with a ? on the photo attached. On this photo you can see the diode at the upper left corner and the PCB of the power supply where I drawed part of the circuit (High Voltage section) to help understanding which diode could be it. thanks in advance for any help! [/img]http://files.engineering.com/getfile.aspx?folder=5c0d49fd-20d5-49e3-bd49-c9

frantal · Joined: 05 Jun 2011 Posts: 5

Sorry, but I saw that no image is attached. I tried with my Mac PPC , but didn't succeed to direct attach. Waiting for advices. Thanks

vtech · Joined: 08 May 2006 Posts: 1264 Location: USA

If you want an image to show it MUST have a direct link to the actual image --not to an html page and it MUST be inserted between the [image]...[/image] tags
Your link points to a html page w/a blank link;

frantal · Joined: 05 Jun 2011 Posts: 5

I hope now is possible to see it:
http://imageshack.us/photo/my-images/717/powersupply.jpg/[/img]

frantal · Joined: 05 Jun 2011 Posts: 5

http://imageshack.us/photo/my-images/717/powersupply.jpg/

vtech · Joined: 08 May 2006 Posts: 1264 Location: USA

Your pix is massive for the forum; resized it. (As a fyi, photobucket is one of the better choices)

Ok, your diode is a 1watt 18 volt zener. as a matter of fact it looks suspiciously close to Panasonics MA2180.
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-24/DSA-471303.html
On many occassions, the number stamped on that type of glass diode denotes it's breakdown (having worked with smps for years I have seen a good many)
Also, keep in mind; on a switch mode power supply failure, there is a good possibility to have a damaged refernce IC which is often placed on the secondary & tied to optocoupler (it is a 3 legged device w/ some iteration of 431) I think it is where I pointed to. Best to replace w/ other parts as it is part of the feedback ckt.

frantal · Joined: 05 Jun 2011 Posts: 5

Many thanks for your help, about this "there is a good possibility to have a damaged refernce IC which is often placed on the secondary & tied to optocoupler (it is a 3 legged device w/ some iteration of 431) I think it is where I pointed to. Best to replace w/ other parts as it is part of the feedback ckt." What you mean it is a double diode marked as SBL1060CT. It is good by testing it bcs the optocoupler too is good on that side and shortened on the High voltage side.Also the resistor 1,2 Ohm is broken (interrupted) and it seems difficult to find a replacement. I will try to send a new image with somme adds to understand. See here under
http://i1233.photobucket.com/albums/ff391/frantal/powersupply.jpg
Thanks to all for helping..[/img]