Need help identifying zener diode.

[zanor]

identifying zener diodes

Hi!

I'm trying to fix my VCR and I found a burned zener diode. But it's not written any value on it.
But I have tried to draw one that looks like it in paint
PLease have a look at the picture below.

 

[IanP]

how to identify a zener diode

I am afraid this is not enough to identify the voltage rating of this diode ..
Try to analise circuit in the neigbourhood of this diode - maybe this will help you to find out / estimate what is the required zener voltage ..

Regards,
IanP

 

[zanor]

identify zener diode

Just found the schmatics for this power supply.
The zener is a ma2180a and searching for that I found out that it is 18V.
But next to the zener there is a 16V capacitor.
How can this work? Or have i just not found the right value for that zener?
Please, have a look at the circuit I have attached.

 

[rtfm]

how to identify zener diode

Just found the schmatics for this power supply.
The zener is a ma2180a and searching for that I found out that it is 18V.

Yes its a 18V 1W Zener.

But next to the zener there is a 16V capacitor. How can this work?

The zener "protects" the capacitor from high voltage spikes coming from the switching supply transformer.

Just replace it by a 18V 1W zener. Connects a voltmeter across the 16V capacitor before switching the main power on. Prepare to switch off if voltage is abnormal as there might be faults in other part of the circuit causing overvoltage on the 16V capacitor.

 

[zanor]

identifying zener diode

Got it working now
At first I got 19V (!) volt across the capacitor but that was before I connected the supply to the rest of the VCR. After I did that I got 14.5V.

Thanks guys!

 

[Sebi]

identifying zener diodes in a circuit

Never test a switchmode supply without load!
As You can see, only the +5V output stabilized, another output voltages depend from load. The 18V zener-protected output with normal load, lower as 14V.