iMac late 2013 no chime and blank screen how to find the problem ?

[stephsa]

Hi,
i just want to know if there are schematics accessible for iMac and also one processing to find if the problem was on the graphic chip. I can reball the gpu if it is the problem. This iMac just dead instantly no sign of graphic problem before

 

[2informaticos]

Start posting 820-xxxx code of logic board.
Any diagnostic LED brights?
You will need to check some signals and voltages on the board.