Swapped all the socketed chips in my 3000T with the ones in my 3000 desktop (known working) except for the memory chips without any change. sigh....
Just curious and admiring your efforts to get the machine going...
Isn't it a real possibility that your power supply has failed? If it is not able to provide enough 'juice' anymore due to age you will have some weird effects. As LED's and things will probably only draw a little current on 5V they might still work.
Jus a guess, maybe you can get a cheap ATX to Amiga PSU adapter cable somewhere to test this...
