Diode case with black band in the middle

[apostal]

I have faulty High Powered Battery Fence Energiser PCB.
On the circuit board there is a diode case component with wide black band in the middle marked as Unknown component on the picture, linked with S2800D Gate. I measured unknown component across with multimeter and it is in 'Open' state. Can it be faulty zener diode? If yes, how then to find the right value without circuit diagram ?

Can somebody help me to identify unknown component on the circuit board?

An externally hosted image should be here but it was not working when we last tested it.

 

[Brian Oshman]

It appears to be a germanium diode.

 

[JonSnell Electronic]

It is actually a Diac. Commonly used in domestic light dimmers and timers.
See DIAC - Wikipedia, the free encyclopedia

 

[tauro0221]

Hi,
Check if the diode goes to the gate of the scr. If it does then it is possible that it is a diac. They use it to trigger scr's

 

[apostal]

Thank you guys for quick replay. If this is DIAC it makes sense why it's open. Before replacing faulty component I had to check if anything else could be damaged before I will power up the circuit board. 🙂

 

[JonSnell Electronic]

Diacs go short circuit when they fail.

 

[simon7000]

Diacs go short circuit when they fail.

For most failures that is correct, but if there is a lot of current they can blow open.

 

[JonSnell Electronic]

For most failures that is correct, but if there is a lot of current they can blow open.

They glass usually breaks in that case and it is obvious.

 

[Andrew Eckhardt]

Yes, and the breakover voltaage (in both directions) is usually plenty high that a junction test setting on a multmeter is useless. You'd need a curve tracer or a current limited adjustable voltage source to actually test it. The good news is it's probably OK.