Unknown iMac compontent DZ6606

[cgwiz89]

Hi there,

I am attempting to repair an old Mid-2011 iMac for the first time and came across a group of burned out components. Some of them are labelled C something which are capacitors however the rest are labelled DZ (DZ6606 for example). I have looked around and even asked and electronic engineer and nobody can tell me what it is! I have attached a photo of the component symbol and the entire schematic page. I just hope it isn't some custom part!

Any help appreciated

 

[Harald Kapp]

Looks like a bidirectional zener diode, 6.8 V.
They are used as overvoltage protection on the respective I/O-lines.