Most of the time when something burns like that it's due to a fault in the power supply. I'm not familiar with the PSUs used in Amigas but there are failure modes where one or more output voltages can go way up and fry a bunch of stuff. I had a desktop PC about 15 years ago where the power supply failed with a bang and in the process it fried the motherboard, CPU, RAM, and video card. I think the sound card and network card survived along with the drives.