[Test-Equipment] TEK 494AP Gain problems

[Fuqua, Bill L]

  I have a Tektronix 494AP who's bain changes as it warms up as much as 8db. It will finally, after a long period of time, stabilize where it should be. However, it is not related to a display board problem or filters. I have looked at the 10MHz output and the IF output changes the same amount. It is the same regardless of resolution bandwidth.
  So it has to be something between the RF input and the 10MHz output. Has anyone encountered this problem before and found the problem?
I noticed some notes regarding the problems on the display board but this is not the cause since the 10MHz IF is before this board.
  Thanks
73
Bill wa4lav