Arcade Otaku - アーケード オタク

Hey guys a really strange thing happened to me, in practice after 15 years of inactivity I pull out of my garage an old pvm2130qm I try it and with immense pleasure I see that it works perfectly so I decide to open it to give it a clean inside. I found a small diode connected to the back of the D board all rusted as soon as I touched it it detached tested and aparently it is dead. It is connected on a resistor (r1529 15K 1/6W) wich is soldered on the other side of the board , now I can't identify this diode also because on the diagram present in the manual this diode is not there, could you help me?

I examined the component with a magnifying glass but nothing is written, I will send better photo asap

Updare, opened another unit and it is nota diac, probably a zener but, it is mounted on a black thermal Pad wicih with aeging becone conductive. This Little diode is just on 50/60hz switch line and can create issue on ntsc sync and v. size (the immage can not fill the screen vertically) so I have removed it and the monitor work flawlessly. I still need to indentify the value of the original part and still understand why it was applied since it is not reported on service manual/scheme.