Zener diode identification

[Michael black]

hi all bit of a newby here I am trying to get an old car ECU reader repaired it is totally dead when plugged in. On looking inside the first thing the power sees is a diode I guess it's a Zener used as a power regulator mainly because it's next to a resistor and the power on a car can fluctuate whether engine running or not. It's packaged like a standard diode black with a silver stripe the only thing on it is 001 and a cross in a circle. I guess it's to keep a steady 12v to the equipment would that be a 12v Zener or is it not that easy? I have checked both ways on the diode and I get inf one way and meg ohms the other I guess that's broke yes?

Mick

 

[Minder]

You cannot test it with a meter on Ohm's range, you need a Diode test range where it provides forward current and shows the volt drop.
It could be a MOV or other suppression device also.
Can you post a pic of it?
M.

 

[ADRT]

Diodes are made to pass current in one direction only. That is why you are seeing infinite going one direction. Sounds to me like the diode is not the culprit. Although using an ohmmeter isn't always the best way to check a diode. You usually need a certain forward threshold voltage to allow current to flow, and an ohmmeter doesn't necessarily put out this voltage.

 

[Michael black]

Hmm okay you test a standard diode with high resistance one way and low resistance the other yes? Zener acts like a diode until it reaches a certain voltage then passes the other way? So it should test like a standard diode, not high resistance both ways or am I wrong? The only reason Iam suspecting is the voltagestopsatthe diode. I have uploaded a pic but nor brilliant.

 

[Michael black]

Q

 

[Minder]

Only if you have a Diode test scale on the meter, a zener will test the same as a normal diode, conduct one way only on a Diode check meter.
In uses it breaks down in the reverse biased mode at the zener rated point.
M.

 

[davenn]

what do you mean " the voltage stops at the diode" ?
a zener isn't in series with the supply

an example......





show a pic of the board of where the diode comes from


Dave