I blew the Chip Mem in my A500 & the 0.5 meg expansion in the trapdoor slot in 1987, sent it to an authorised Amiga repair center they replaced the chips on the motherboard & I bought a new trapdoor expznsion.
When booting the screen only displayed white then grey & after green.
Take a look here at the
Self Test Output paragraph two second bullet point
http://www.amigahistory.co.uk/selftest.html Good luck
