Got this Amiga 500 Revision 5 computer in a non working state. Initial problem was a black screen. Upon reseating the AGNUS chip, the machine showed a green screen. Green screen usually means bad RAM, first thing I tried was to burn an EPROM with DIAGROM and fit it in the ROM socket with an adapter for revision 5 motherboards. DIAGROM was unable to show me something on screen via the RGB video output, so I connected another computer to the AMIGA with a serial cable. With this method the output of DIAGROM was that the chip RAM was bad, the problem is that we still need to identify which ones are the bad ones, there are 16 RAM chips soldered to the pcb.
I tried the ‘piggyback’ method, it consist in adding a chip in top of another, in this case I’ve placed a RAM chip in top of the soldered ones. I added 16 chips, and the green screen went away, it showed random patterns on screen. Then I proceed to remove RAM chips one by one (the piggyback ones) until the green screen came back.
Upon removing all the piggyback chips and leaving just the one that made the machine output a green screen, the AMIGA booted into the WORKBENCH prompt.
With the defective chip identified, I just cut the legs for an easier removal. New socket and new RAM ic and problem fixed.