identify a diode

[timwebb22]

so im working on a amp and i cant figure out what kinda zener diodes these are.the 4 big ones any help?

[999999999]

Re: identify a diode

MELF (metal electrode leadless face) form factor, you'll have to measure it to get the size, though from the pic I'm guessing it's 5mm long, 2.5mm diameter, SM1 - LL41 (DO-213), 500mW or 1W, of unknown voltage.

Example, but something is screwy, it's also listed as through-hole http://www.mouser.com/ProductDetail/...%2f5cxbpMAc%3d

[budm]

Re: identify a diode

Did you try taking any DC reading on them yet, or do they check out bad?

[Agent24]

Re: identify a diode

Depending on the manufacturer, the blue stripe could indicate a specific voltage or it just might indicate what you already know, that they are zeners.

If you don't have a schematic I think you'll have to test one or all of them and find out what they are.

[timwebb22]

Re: identify a diode

they all measure about .15 in diode check. they are all dead.

[Agent24]

Re: identify a diode

I don't think the standard diode test function of a multimeter can test a zener correctly, in any case if you are trying to measure some property of the diode in-circuit you may get incorrect results.

[b700029]

Re: identify a diode

Depending on the manufacturer, the blue stripe could indicate a specific voltage or it just might indicate what you already know, that they are zeners.

Or it might just be for polarity.

[budm]

Re: identify a diode

"they all measure about .15 in diode check" reading is taken with diodes are off the board right?

[Agent24]

Re: identify a diode

Or it might just be for polarity.

Well sure, it will be for polarity, the stripe is... but often (for SMDs) the colour of it indicates something else as well

[digitalscorpion]

Re: identify a diode

Maybe i missed it, but what is the make/model of this amp? Perhaps someone has a schematic/BOM...

[999999999]

Re: identify a diode

Pretty sure they are zeners due to "ZD" silkscreen on the board. Not sure how voltage could be designated with only one color band, there are so (too) many different possible voltages...

The mosfets on the board are rated to 60V, you could use a variable voltage supply up to that voltage range, increasing supply voltage till you measure zener conduction to get a voltage value, or conclude they are blown if it supply reaches 55V without. They'd have to be off the board to test. Example (though a multimeter is fine, no analog panel meter need): http://www.instructables.com/id/Zene...cker/?ALLSTEPS

[selldoor]

Re: identify a diode

Hi I believe the blue stripe is for polarity.
Digikey have a pile of these - I dont know how you decide which voltage.
Have you taken one off the board - perhaps more info underneath?
Digikey ones appear to have a white stripe in the middle which may have some id code on it. - Suggest give DK a call and ask them how they id them?

[Agent24]

Re: identify a diode

In general they ID them from the box they come in from the manufacturer. Some SMD parts simply have no useful markings for identification (diodes and some transistors), and SMD ceramic capacitors and inductors generally have nothing at all.

Some Zeners have colours to determine voltage, but it's only from some manufacturers, for example: http://www.marsport.org.uk/smd/sod80.htm

I think in this case however, the blue stripe is just saying "Zener" which is of course not helpful because we already know that.

[selldoor]

Re: identify a diode

It indicates two things , although I dont think all manufacturers stick to the codes!

In your link it says: The cathode end is indicated by a coloured band.

and for a Mini Delf a Zener is Blue - Id guess it will be the same for a DELF

[budm]

Re: identify a diode

I am still surprised that ALL of them shorted out, otherwise if one is good then it can easily be figure out the Zener voltage using power supply, resistor, and DMM.