This entry can also have a title "Being Lucky with This One". I got this Commodore Amiga 500 on eBay. These were one of the most exciting machines back in mid 80s. When I tried to turn it on it would turn green screen, flash several times, then re-boot and a do it all over again. Please note that I did not have any previous experience with Amigas. I had an Atari 520 ST back in the good old days.
Symptoms
Amiga does not boot, it comes on with green screen, screen flashing (I think someone mentioned 11 flashes before reboot), and then reboot. Doing this continuously. After some reading I found that it could be either bad RAM or issues with Angus chip.
First Attempt
First, I tried opening the Amiga, doing some alcohol cleaning of the board and especially PLCC socket and Agnus chip without removing the chip. I tried the thing while still open and it booted properly and asked for OS disk. I put everything back together. Turned it on and got where I was before. No go.
Amiga 500 is the one on the right. On the left is an Atari ST 1040 probably the biggest rival at the time. Although, ST folks (I was one of them back in 80s) and Amiga folks kind of found their way of mutual respect and little bit different interests.
Second Attempt
I purchased on of those PLCC chip extractors. You can see it in the picture above. Me and my assistant (also in picture) opened this Amiga again gently.
Removed the top cover and the keyboard. Please not that to remove keyboard you need also to disconnect the ground wire connected at the floppy. Kids, do try this at home, we are not professionals. Well, I am kidding there, if you are attempting this be very careful and gentle. This is an electrical device (no playing when it is powered on and connected) and any fault play can easily damage it.
And located Mr. Agnus again.
Now, we used PLCC chip extractor. Here you have to be very careful not to damage the PLCC socket nor the actual chip. Some people on net mentioned use of two small screw driver to remove this chip. Never do that with any PLCC chip especially if the socket is old. It will break. We successfully removed the chip. I used some rubbing alcohol to clean the socket and the pins on the chip. I could not see any damage. After good cleaning, we snapped the chip back into the socket.
After half assembly back, we tested the machine while still open. We got the picture on, which was a good sign. My second "assistant" got interested here. One thing my kids learned from me is that old computers are fun, very often much more than the new ones.
We put everything together (keyboard, cover top), popped in a floppy with good old Indiana Jones game and ran a test drive.
I reckon we got lucky with this one, at least for now. If you have an Amiga with similar symptoms there is a big chance you have Agnus chip issue or bad RAM. In this case, it seems that little bit of cleaning and re-seating the chip nicely into its socked helped.
References
http://eab.abime.net/showthread.php?t=23908
http://en.wikipedia.org/wiki/Amiga_500
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