[ronbryan]

If you have the manual, I would check the DC supplies are within limits. To make sure that the pre-scaler chip is getting enough RF signal, you could go through the input amplifier calibration procedure, adjusting R19 if necessary.

If you put an AC coupled scope at a fairly high gain setting on the 'Sync Out' connection, when the generator is locked, what does the control voltage look like? I think the design provides a current output, to be fed into a summing network in the TF2015, but it might give a clue if the variation is random, rather than periodic.

Although you have two TF2015 signal generators, which should eliminate a problem with that area, I have had an unsoldered connection to the 'Counter Out' connector, which gave low amplitude to that signal, which is used as the input to the TF2017. It should be no problem to check that you are getting >80mV output into 50 ohm from that point - in fact I'm sure that my generator gave more like 300mV once working properly.

I cannot remember for certain, but I think there are some 'vias' on the top logic board, possibly on power supply rails, that might need checking or re-soldering. Maybe someone else can clarify that.

If all else fails, you could go through the 'Circuit Checks and Adjustments' in the manual. The only other fault I have had with my unit is with one of the BCY71 transistors in the output amplifier, but in that case the fault was not the same.

Ron