specing a diode

aidanki

Hi all,

I am looking for a diode to replace one that rotted off a circuit board. I have a few other identical circuit boards around, they are in use so I can't simply take one out of one of these and replace it.

I guess Im looking for some help on how I measure the spec of the diode that I am looking for.

I have a multimeter so today I put it across the terminals of the diode on another circuit board. My multimeter has a diode check function as decribed here http://www.allaboutcircuits.com/vol_3/chpt_3/2.html.

Make a long story short when measuring across the terminals of the diode I got a reading of 620

Per my multimeter manual the test condition when using the diode forward voltage test function is "opencircuit voltage is ~2.8V."

So with that info what should I be looking for when I start going online to source a diode

There are no markings on the diode itself nor on the circuit board

PrzemoF

"Diode" is a broad term - you have to narrow down what the diode is doing. Any chance that you couls post good quality photo of the board? And/or name of the device? There might be a wiring diagram somewhere on the net, so we could find exactly what kind of diode you're looking for.

DublinDilbert

You measured 620mV across the diode, which is correct for a forward biased silicon diode.

That diode isn't your issue, must be something else...

longhalloween

Diodes can vary in appearance so throw up a picture.

ZENER

DublinDilbert wrote: »

You measured 620mV across the diode, which is correct for a forward biased silicon diode.

That diode isn't your issue, must be something else...

The result was from a known good board if I read the OP correctly. Measuring a diode in circuit is never going to be reliable. Desoldering one end and lifting it from the PCB is a better method.

Power rectifiers like a 1N4005 will have a VFWD of about 0.415V, signal diodes will measure higher (silicon) or lower (germanium). Impossible to help without a description of the circuit or at the very least - a picture and a clue about what the circuit is doing.

Ken

aidanki

yes the measurement was taken from an identical board that is working perfectly. I was hoping to take the measurement from a good board and then get a replacement diode and solder it in place

tigger1962

as other have said a photo, description or any writing on the good ones might help.

aidanki

will have to wait a few days for the photo no camera to hand...........

the diode is blue in colour with a few coloured bands on it, does the colour of the bands signify anything ?

from what I can see from backround reading the coloured banding on resistors means quite a bit, what does coloured banding mean for diodes ?

PrzemoF

it could be this: https://en.wikipedia.org/wiki/Electronic_color_code#Diode_part_number

ZENER

Assuming it complies with the JEDEC scheme mentioned above then the first digits are assumed to be 1N the remaining numbers will follow the colour scheme shown here.

There are many components that might resemble a diode in in most cases they will be just that but there are many many different types of diode (see my name ). Hopefully the component you have is easily identified.

Measuring the Vfwd of a diode won't help much in its identity other than to distinguish between germanium and silicon. Zeners (or more correctly "avalanche") diodes have a set reverse breakdown voltage and are doped to have a specific value.

Ken

aidanki

ZENER wrote: »

Assuming it complies with the JEDEC scheme mentioned above then the first digits are assumed to be 1N the remaining numbers will follow the colour scheme shown here.

There are many components that might resemble a diode in in most cases they will be just that but there are many many different types of diode (see my name ). Hopefully the component you have is easily identified.

Measuring the Vfwd of a diode won't help much in its identity other than to distinguish between germanium and silicon. Zeners (or more correctly "avalanche") diodes have a set reverse breakdown voltage and are doped to have a specific value.

Ken

I guess im kinda a novice when it comes to electronics, I did Mech Eng in college so have an idea of the basics..........bit rusty now though

Is there any book/cd/tutorials I could start with for learning the basics about circuit boards etc

Alun

Someone with the user name ZENER should know a lot about diodes, I'd listen to him