Got it a few months ago from some family.
It worked fine till yesterday. I was trying to unpack a LZX file, when suddely the 1200 made some strange noises and went black.
I had some flickering on de 1940 amiga screen before it shut down.
My amiga 500 doesn't have that flickering on de screen, maybe it was a sign?
Start with the power supply, are the voltages there and close to +5,+12 and -5v?
Work from there, look for any leaking caps or bulged ones.
mech