HP Laserjet 9000, 9040, 9050 Printer

Question:
After printer warms up (30 minutes) the display goes blank, back lighting still on, goes off the network. Cycle power still no good. Turn the printer off for a few hours printer works great till it warms up again.  Replaced formatter, DC Controller, same problem
Response:
If the engine test is ok that eliminates the power supply and dc controller.  What about the memory and firmware.  Did you move from the old formatter to the new or are you using the same memory.  That could be the issue.  Also after it comes back on run an event log from the diagnostics menu and see if the latest error is at the current page count.  If it is what is the error or event message?