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Removal and Adjustment of ZC1 Tuning Dial Mechanisms

by Chris Underwood ZL2CU

 
 
 
Refurbishing Tuning Dial
 
 
 
 
 

Many ZC1's have tuning mechanisms that seem rough or sticky when used.  Unless there is evidence of mechanical damage in most cases a few simple adjustments can fix the problem.

While the dial mechanisms for Mk-1 and Mk-2 sets are essentially identical there are some small differences that have to be considered.  These differences will be covered as they arise.

   
PART ONE
  1. Remove set from case.
  2. Loosen the screw clamping the rear end of the dial mechanism to the tuning gang. 
  3. Remove fine tune knob.
  4. In theory the tuning mechanism should now be able to be easily withdrawn from the set.
    1. In practice it will most likely be still stuck to the tuning gang
    2. Rotate the tuning knob anticlockwise until it hits the stop.
    3. Place a small piece of wood across the fully closed tuning gang then firmly pressing on the wood to prevent the gang from opening gently, but firmly, rotate the tuning knob clockwise hopefully breaking the oxide coating gluing the tuning mechanism and gang together.  Once this coating is broken, and hopefully nothing else, and the mechanism free then,
  5. Turn the "flick tune"  knob to "flick tune", this also causes the "fine tune" drive wheel to lift away from the scale plate of the tuning dial. 
  6. Carefully withdraw the dial assembly from the set.
    1. Caution.  As you remove the assembly turn it to line up in turn each of the "V" notches cut in each flick tune setting plate with the "flick tune" detent springs located on the inside front panel just above the tuning mechanism.  Failure to do this makes it hard to remove, or replace, the dial assembly and can damage the detent springs and "flag assemblies".
    2. It may also be necessary to hold the fine tune drive wheel down further out of the way so that it doesn't catch on the scale plate while you remove the dial assembly.
 
 

With the dial assembly removed the V notches in each flick tune setting plate are clearly visible.

One of the reasons setting up a flick tune frequency is hard or impossible to do is that the flick tune plates have become stuck.  The two plates, with all four locking screws loosened, (the coloured screws protruding the front of the large bakelite knob) should be able rotate smoothly and independently.

In my experience this is rarely the case.  Probably because of disuse over many years the plates have become glued in place by a combination of dried out lubricant and oxidisation.  However records exist that indicate these assemblies sometimes suffered from lack of quality control in their assembly.

With the dial assembly removed it is easy to check if the plates are stuck. 

Rear view of Dial Assembly

   
 

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Light finger pressure should enable each plate to rotate smoothly and freely in either direction.  If the plates are very stiff, stick in places or simply won't rotate the assembly will have to be dismantled and cleaned.

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To disassemble the dial assembly proceed as follows.
  1. Unscrew and remove coloured locking set screws.
    • Note the Mk-1 Red screws hold the dial scale plate to the "hub Assembly", the Red screws of the Mk-2 and the Grey/Blue screws of both Mk's pass through the scale plate.
  2. Unscrew and remove small screw in centre of the bakelite knob.
  3. Remove the knob and scale plate together.
  4. Unscrew and remove screw from locking clamp fitted to rear of dial assembly.
    • Note shaft of assembly is grooved to hold screw and clamp cannot be removed with screw in place.
  5. Remove locking clamp from assembly.

Dial Assemblies with Knob and Scale Plate Removed

Photo shows differences between the Mk-1 (left) and Mk-2 (right) assemblies.

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Differences are;
  1. The Mk-1 lacks a dust shield.
  2. The Mk-1 locking clamp is squared at the locking screw end and rounded on the Mk-2.
  3. The colour of the Grey locking screws on the Mk-1 is changed to Blue on the Mk-2.
  4. The red locking set screws on the Mk-1 have a short section turned down above the threaded portion.
    • Note; Thread is 3/16 inch BSW.

Mk-2 set screw above Mk-1 set screw below.

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With the knob, scale plate and rear clamp removed it is now possible to strip down the flick tune locking sub-assembly.

Carefully bend the two "wings" on each of the two retaining clips inwards so that the clips can be withdrawn from the reverse side of the assembly.

The two die-cast rings and their associated flick tune setting plates can now be gently pried off the die-cast central hub.

In many cases it will be found that the flick tune setting plates are firmly "glued" by a combination of dried out lubricant and oxidisation.

Holding the setting plate in your fingers use your thumbs to carefully push the die-cast ring out of the centre of the setting plate.

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Although the surface area holding the two parts together is not very large in some cases the two parts are strongly "glued" together and it can take some force to break them apart.  Be careful to spread the load of your fingers on the setting plate so that in extreme cases you don't inadvertently bend it.  Using your fingers rather than a vice allows you to feel what's happening.

Repeat the process for the second setting plate and ring after removing it from the front of the hub unit.

Clean the parts to remove all traces of old lubricant.

If you have a 3/16 inch BSW tap you may wish to clean the two threaded holes on the rear ring.

Flick tune setting plate and die-cast ring

   
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Mk-1 Dial Assembly Fully Stripped Down

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Putting it Back Together.
  1. Try fitting a cleaned die-cast ring to a flick tune setting plate.  It will most likely fit tightly and be difficult to rotate.

    • Given that it would seem easier to make a new flick tune setting plate than a new die-cast ring.  The centre hole in the setting plate should be carefully enlarged using a piece of fine Emery cloth.  Take your time and constantly try fitting the plate to the ring.  Gradually it will become easier to rotate.  Keep going until the plate smoothly rotates without any trace of sticking.  The fit of the two pieces should still be close but not tight.  No lubricant is necessary to obtain smooth operation but application of a dry lubricant such as Graphite powder commonly used in locks is recommended at final reassembly.

    • Be careful not to reduce the thickness of the setting plate.  When fitted the setting plate must be slightly "Proud" of the die-cast ring or the locking action of the flick tune will not work.

  2. Repeat process for the second set of die-cast ring and flick tune setting plate.

  3. Select the set that fits to the front of the main assembly Hub. 

    • Note: The die-cast ring of this set has two sets of holes through it. One set of four for the retaining clips, and one set of four smaller diameter unthreaded holes to take the set screws.

    • The rear facing die-cast ring has three sets of holes. One set of four for the retaining clips, one set of two unthreaded holes for the Grey or Blue set screws and one set of two threaded holes for the Red set screws.

  4. Take the two Grey coloured set screws (Blue if a Mk-2 Set) pass them through two diagonally opposite smaller holes of the die-cast ring of the front set and screw them into the front of the Hub of the dial assembly.  The setting plate should be fitted facing the hub assembly.

    • Check that the flick tune setting plate is able to freely rotate with the two set screws not fully tightened.  The screws must be tightened sufficiently so that the flick tune setting plate is held properly centered in position by the die-cast ring.

    • Check that when the set screws are "finger tight" that the die-cast ring and setting plate are locked together and the plate cannot be rotated on the die-cast ring

    • If all OK then,.

  5. Take the two Red set screws and pass them through the remaining two hole of the smaller set on the front die-cast ring and through the Hub assembly so that they protrude.

  6. Carefully fit the second set of die-cast ring and flick tune setting plate ensuring that the unthreaded set of smaller holes fit over the ends of the Grey/Blue set screws.  This should line up the ends of the Red set screws with the set of small threaded holes.  Screw the Red set screws into the threaded holes.

    • Check that the flick tune setting plate is able to freely rotate with the two Red set screws not fully tightened.  The screws must be tightened sufficiently so that the flick tune setting plate is held properly centered in position by the die-cast ring.

    • Check that when the set screws are "finger tight" that the die-cast ring and setting plate are locked together and the plate cannot be rotated on the die-cast ring

    • Warning:  On the Mk-1 assembly with the scale plate removed it is easy to screw the Red Set screws too far through the rear die-cast ring attempting lock the flick-tune Set plate.  It is then possible to screw them up hard against the die-cast clamp and shatter it into several pieces.   See photo above labeled "Dial Assemblies with Knob and Scale Plate Removed" and you can see the problem occurring on the Mk-1 assembly.   Yes I learned the hard way!  For this reason it is best to fit the clamp only after the scale plate is fitted.

         

    These cast clamps have the reputation of being extremely brittle.  Possibly they were cranked out too fast from the extruding machine and are full of stress flaws.

    They are also very easy to break by the over tightening of their clamp screw.

    Fortunately I had a spare but if you suffer this misfortune and can't find another genuine clamp a suitably sized Hose clamp (Jubilee clip) would be an effective substitute.

     
         
  7. Fit the two retaining clips and carefully bend their "wings" back into shape so that the assembly is held together.

    • Check that the Flick set plates are still free to rotate with the four set screws loosened.

  8. Fit locking clamp to rear of the assembly hub.

    • Ensure that the clamp is fitted with the clamping screw on the right when the split in the clamp is facing downwards.  If this not done extreme difficulty will be experienced in trying to tighten the screw when the assembly is refitted to the set.

  9. Remove the two Red set screws on the Mk-1and refit knob and scale plate.

    • Note on the Mk-1 the Red set screws pass through the two small diameter holes on the scale plate.

    • Note the scale plate can be fitted to the centre hub in one of two positions.   The correct position is with the 3.5 MHz (centre scale) roughly opposite the position of the slotted square face of the clamp.  In the alternative position the scale will be upside down when fitted although it will not appear to be so initially.

    • On the Mk-2 the large knob and scale plate is easier to fit with two screws of any colour removed but this is not essential.

  10. Refit the two Grey/Blue set screws.

  11. Fit and tighten screw in centre of Bakelite knob.

  12. Check Dial assembly still operating properly.

  13. See Part 3 for refitting assembly to set.

 

1 - 2 - 3

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PART ONE  Adjusting ZC1 Tuning Dial Mechanisms

PART TWO Flick Tune Flags and Actuating Linkages.

PART THREE Refitting Dial Assembly to set.

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top                                                                                         September 2011