[time-nuts] Issues with Datum FTS 4065A cesium beam reference

[AC0XU (Jim)]

Time Nuts-

Having fixed the dead power supply on this Datum FTS 4065A, the control panel displays mostly "Major" fault, although this occasionally shifts to "Minor" fault for a brief time. It reports Cesium Module faults that vary from time to time. They are usually one of:

2,18
2,3,18
2,3,7,18

According to the 4065C manual, the codes mean:

2 - Voltage difference (symmetry check of clock transition) > 40 mV
or
Voltage difference (clock pedestal) >40 mV

3 - Voltage difference (Zeeman pedestal) >160 mV

7 -  DAC voltage < 5% or > 95% of input range

18 - Beam Gain DAC Near Limit

Is there a straightfoward way to determine whether the tube is dead or - how should I drill down??

All voltages displayed by the control panel seem to be within range. Oscillator shifts from 'COLD' to 'warm'. There is a 10 MHZX output signal but it is not especially stable.

Thanks in advance-

Jim