[R-390] revised PTO endpoint adjustment (long)

Wed Mar 11 11:49:49 EDT 2009

Good procedure.

I just wanted to add that if you do not have a frequency counter, you can "listen" to the PTO on a calibrated HF receiver by listening to the 2455 and 3455 signals, either with BFO on or SSB mode.

73 Tom 

--- On Wed, 3/11/09, wli <wli98122 at yahoo.com> wrote:

> From: wli <wli98122 at yahoo.com>
> Subject: Re: [R-390] revised PTO endpoint adjustment (long)
> To: R-390 at mailman.qth.net
> Date: Wednesday, March 11, 2009, 10:15 AM
> Hi. Have revised the previous post thanks to the comments
> received. Here is version 2.0
> --------------------------------------------------------
> PTO End-point adjustment
> W. Li
> 
> 1. From top of receiver, disconnect mini-BNC plug P217 and
> drop it thru the chassis hole to the bottom side. This coax
> carries the PTO output.
> 
> 2. Disconnect P116 mini-coax from rear panel
> 
> 3. Remove J116 from rear panel
> 
> 4. Tune the MC dial to 7MC (I did this in anticipation of
> further RF work)
> 
> 5. Tune the KC dial up to (+) 000
> 
> 6. Turn receiver over so it is up-side-down on the bench
> 
> 7. Remove Oldham spring using a fine forceps clamp (may
> have to rotate the KC dial a few degrees so that you can get
> at both ends of the Oldham spring). Tie a string on the
> spring before it flies off.
> 
> 8. Do not touch the KC  dial again until  step 28. Consider
> locking it.
> 
> 9. Remove both stainless steel 6-32 screws off of the
> trapezoidal metal support bracket on the back of the PTO. 
> This support secures the rear of the PTO to the chassis. Do
> not disturb the single green captive screw.
> 
> 10. Loosen both front green 8-32 captive screws. The entire
> PTO subchassis should now be free to slide aft.
> 
> 11. Wiggle the PTO subchassis and  slide it aft about an
> inch to free it from the KC shaft. The Oldham coupler will
> come apart and the center disc will fall free... save it.
> You now have one Oldham disc attached to the KC shaft, and
> the other  Oldham disc attached to the PTO shaft, and the
> middle one loose somewhere.
> 
> 12.. Tilt PTO chassis upwards 45 degrees. Rest it on small
> plywood shelf so the rear bracket sits down in its
> compartment, and the front rests up on the chassis cable
> loom. This exposes the front of the PTO . Note: the cable in
> the back with the blue plug carries power to the PTO and is
> left attached.
> 
> 13. Use J116 to adapt the PTO's mini-BNC to a standard
> BNC jack.
> 
> 14. Hook up your frequency counter to J116 using a short
> BNC cable
> 
> 15. On the front face of the PTO, remove the large
> hexagonal adjusting screw cover behind Z702. This cover
> screw has a very shallow thread, and comes out in 2 turns.
> Store it with the small Oldham spring for later.
> 
> 16. Plug in the receiver and counter and allow an hour or
> longer to warm up and stabilize the electronics.
> 
> 17. Using your hand, slowly twist the Oldham disc on the
> PTO shaft until the counter reads exactly 2455. Look at the
> counter to figure out which way to turn. Note: the PTO has
> its own stop, which can be easily damaged. GO SLOW.
> 
> 18. Using the Oldham spring post as a point of reference,
> mark the front PTO plate with a pencil as your start point. 
> 
> 19. Now manually rotate the Oldham disc on the PTO shaft
> exactly ten turns. Watch the counter readout rise as you
> turn. Stop at exactly ten turns lining up the spring post
> with your pencil mark. The counter now reads something
> fairly close to 3455KC. 
> 
> 20. Without any further rotation of the PTO, turn the tiny
> PTO adjusting screw with a fine screwdriver until the
> counter reads exactly 3455KC. 
> 
> 21. Go back about ten turns, stopping when the counter
> reads exactly 2455KC..
> 
> 22. Chances are your start point will not align with the
> spring post, so erase the old pencil mark and make a new
> one. Changing one end-point alters the other.
> 
> 23. Now hand rotate the PTO shaft exactly 10 turns the
> other way and see how close you end up to 3455KC. Chances
> are you will be off a bit.
> 
> 24. Readjust the PTO adjusting screw again, so that the
> counter reads exactly  3455KC
> 
> 25. Repeat steps 21-24 as often as necessary until 10 turns
> gets you from precisely 2455KC to 3455KC.(this took me 6
> cycles of fooling around). Note all the PTO adjusting screw
> tuning  is at the 3455KC end. All you do at the 2455KC end
> is redraw your pencil mark.  
> 
> 26. OK, now the PTO has the correct frequency range of
> 1000KC in exactly ten turns of the PTO shaft
> 
> 28. Be sure the KC dial is unlocked. Gently turn the KC
> dial down as far as it will go until it is stopped by the
> 10-turn stop. The Veeder-Root  should now read between -963
> and -972. If it does not, adjust the ten-turn stop until it
> does (another issue entirely).
> 
> 29. Rotate the PTO until the counter reads exactly 3455KC
> 
> 30. Rotate the KC dial up a few turns until the Veeder-Root
> reads exactly (-) 000, and lock it in place.
> 
> 31. Stick the middle Oldham coupler disc to its mate on the
> PTO shaft with a blob of grease. 
> 
> 32. Replace the large cover screw you took off in step 15. 
> 
> 33. Now loosen the Bristo screw clamp nearest the KC dial,
> so that the Oldham coupler nearest the front may rotate on
> the KC dial shaft to mate precisely with the Oldham coupler
> disk of the PTO shaft. Since the KC dial is locked, only the
> Oldham disc and its clamp will rotate. Take great care NOT
> to rotate the PTO shaft. You can tell if you do inadvertedly
> rotate it, because the counter will show a change in
> frequency.
> 
> In some cases, there is no room to access the Bristo clamp
> on the KC shaft. Plan B is to loosen the Bristo clamp on the
> PTO shaft, so that it can rotate to mate with the other
> Oldham disc. Here again, you must not allow the PTO shaft to
> rotate whilst you fiddle with the Oldham disc. There is no
> way to lock the PTO shaft, so great care must be taken not
> to move it. Again the counter will detect any rotation of
> the PTO shaft at this time.
> 
> 34. Now you can slide the entire PTO subchassis forward to
> mechanically re-engage the Oldham coupler........ this step
> is to mechanically synchronize the PTO to the rest of the RF
> gear train. This will require minute fiddling of the now
> loose Oldham coupler disc as the fit is very close.  Take
> your time in getting all the Oldham discs to mate.
> 
> 35. Loosely start both 8-32 green screws in, to stabilize
> the PTO chassis
> 
> 36. Now that the coupler is together, both the PTO shaft
> and the KC dial shaft will rotate together. The KC dial is
> at  (-)000 and the counter shows 3455KC.
> 
> 37. Unlock the KC dial now.
> 
> 38. Rotate the KC dial up slowly and gently until the
> spring posts are accessible for you to replace the Oldham
> spring. Note that the PTO shaft will also rotate the same
> amount since the coupler is now mechanically engaged.
> 
> 39. Wiggle the PTO such that both PTO and dial shafts line
> up, and so that there is a small gap visible between the
> Oldham coupler discs. At this point, if things are tight,
> you can gain an extra mm by loosening the single rear green
> screw. 
> 
> 40. Tighten the Bristo spline clamp on the shaft of the KC
> dial
> 
> 41. Secure things by tightening down both front green
> screws, and reinstalling both rear deck 6-32 screws.
> 
> 42. Now that the PTO is physically secured, do a final
> electrical check on the PTO with the counter. Turn the KC
> dial to (-)000. The counter should read exactly 3455KC. Now
> run the KC dial up to (+)000. The counter should read
> exactly 2455KC. This is the whole reason for setting the PTO
> endpoints.
> 
> 43. If you can not get exactly 1000KC in ten turns, go back
> and redo things until you can.
> 
> 44. Disconnect the counter, and restore the mini-coax
> interconnections.
> 
> 45. Final check: tune in WWV, it should come in exactly at
> 5MC, 10MC etc
> 
> 46. You are done
> ---------------------------------------------------------------------------------
> 
> 
> 
> 
>       
> 
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