A4000 getting flaky- need a quick checklist

[CRL]

Hi All-
My A4000 (stock internally except for Sonnet quaddoubler 68040(50mhz)) has been running ontinuously for most of a year. In the last week it has frozen up every time I turn it on after about an hour or so.  I cleaned out the battery a year ago.  I haven't added any new softwear.  I did blow the dust out of the fans, but that made little difference.  If I was getting guru meditations I might have some clue, but the solid freeze has me spooked.  (I left it running because my cheap add-on flickerfixer/scan doubler wouldn't stablize until it had been running for 5 minutes or so.)

A few ideas to try or things to check would be appreciated.
CRL

[CRL]

Hi All-
Thanks for the checklist.  I finally took off the lid and started it up to see what I could see (I wondered if the muffin fan on the quaddoubler had quit and let the CPU overheat), and discovered that the fan in the PSU had frozen up.  Looks like I will have to replace it and maybe do a preventative replace on the capacitors as well.(?) An overheated PSU could account for the symptoms if I read the checklist correctly.  I have done some electronic hobby building about 40 years ago, but nothing since.  Anything I need to watch out for as I dig into the PSU?
Thanks for the help- this comunity is the greatest if not the crazyest!
CRL

[CRL]

Hi All-
Just a note to say my A4000 is running again.  I found an exact replacement muffin fan at Radio Shack (pricy, but oh well).  Blew out 14 years worth of dust and everything looked shiny, clean and OK.  No bulging or sagging or melting or brown colors from heat.  The big PSU caps were rated for 85C and looked like new.  I put in the fan, reassembled the PSU, the computer, and it ran fine.  I did break the flimsy and brittle power switch on the PSU, but I never used it anyway.  Thanks for the suggestions of where to start.  Thought you guy would like to know there is one more Amiga amoung the living.
CRL