Mechanical Repair HP 5255A (plug in for 5245L) 'Frozen' Dial

[VK5RC]

Having repaired my 5245L https://www.eevblog.com/forum/repair/repair-of-hp-5245l-nixie-frequency-counter/ -  a lovely beast - I am slowly getting some of the many plug ins that are available (and some other 1960s counters).

The 5255A is a heterodyne type frequency converter that takes the 1MHz reference signal from the main counter, multiplies it many times (to 200MHZ first) then mixes it with the signal to be measured (3-12GHz),mixing it down into the 50MHz bandwidth of the 5245L.
The 5255A uses a tuned cavity to select the Nth harmonic of the 200MHz derived from the 5245Ls reference, the harmonic frequency selected is determined by the mechanics of the cavity, controlled by some lovely gears. See HP Journal http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1964-06.pdf

My unit had a problem in that the 'Knob' would turn freely - and would appear to reach end stops - but the 'Dial'  (indicating the approximate harmonic being tuned) would not move at all. See Front Photo.
A manual is available from Keysight (Thanks guys!)  but isn't a lot of help with the mechanics.    http://literature.cdn.keysight.com/litweb/pdf/05255-9031.pdf?id=1869245

After quite a bit of experimentation, access to the area requires removal of the entire bottom aluminium plate - see photo Access.The front Knob is removed by an imperial Allen key, and the Dial by Phillips screws. Also removal of other screws holding on the front cover is required. The front cover can then be moved forward little to gain access. See Photo Gears
There is a shaft - labelled  A in the below photos, and the gears B and C are swaged together, and D and E should be swaged together but weren't in my unit. The lubricant between the shaft A and gear E had dried - fixing gear E (and the Dial that it drives eventually) very firmly to the chassis . gear D was being driven very nicely and rotating around the swaged area. With apologies to robrenz (a mechanical genius) a few well punched divetts again linked gears D and E. See photo gears 2.
Hope this is of some help to others.
Now on to the electrical fix!