When I switch on my 8500 the picture is out of focus and it seems all stored setups are gone. If I enter the service menu the stigmator adjustment is not available when it is there. After switching off and on many times things come back to normal situation.
Is it a matter of cleaning some contact on some board? If yes which is the board affected? Is it better to remove the boards clean all contacts and reseat back the boards?
Any help will be appreciated.

Gianfi

I would start with CLM board and daughter boards on it.
Mauro

Maybe the 3V backup battery need to be checked/changed ?

It sounds like it needs a thorough cleaning at the board level. It's been discussed alot here but the search engine here won't make it easy to find so I'll give a quick overview.
It isn't difficult to do but make sure everything is dry before powering up when you're done. Get some Deoxyt or denatured alcohol, a small soft parts brush, (an old toothbrush will work), a can or two of compressed air, and a chip puller (PLCC type) and clean everything with contact points. This included card edges, LVPS and HVPS male contacts and daughter boards.

Do NOT use a small screwdriver to try to remove the chips. Been there, broke that.
Do NOT use a pencil eraser to "clean" anything.
DO unplug the pj and wait at least 10 mins before removing any boards.

Again, let it dry well before powering it up. Some people advise letting everything sit overnight before putting it all back together and energizing it. I just went nuts with the canned air and dried everything well.

This is the best place to start high level troubleshooting if needed.

Greg