I have previously upgraded Timebase for Agilent/HP 53132A Universal frequency counter and also PM66xx Counter. This time i will be upgrading Keysight 53220A.
This upgrade is going to be little different as keysight 53220A does not have a oscillator module. OCXO is directly soldered to the main board. So this upgrade is just going to be desoldring existing TCXO and mounting correct OCXO to have Option 010 Ultra High Stability OCXO Timebase activated.