Arrived at SL1 oscillator output - it is unstable (wandering over a few hundred kHz.)
Re-confirmed stability of N1, N2, N3 and SL2 outputs using a second instrument.
Attached is photo from SL1 phase error test point.
Next stop is the 8660B main service manual, as the 00070 manual goes into no further detail at this point (there are three plug-in cards and possibly other components involved.)
