A590 problem, advice would be appreciated

[arttu80]

Also you may check if your A590 have "self powered" -hack, which would look something like this -->

http://members.iinet.net.au/~davem2/overclock/a590.jpg

If it does look familiar, you must have more powerful power supply on your Amiga 500 and ofcourse leave disconnected A590 power supply.