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Repair of ZC1 Power Supply Vibrator Units

 
 
 
 
 
 
 
 
 
 

The 12 Volt vibrator units type V6295 as used in the ZC1 radio series are normally fairly reliable devices given their age, typically 60 + years, and the fact that they are largely mechanical devices.

However they can be prone to the following faults

  • The most common problem is oxidised contacts if left unused for more than a few months without use.

  • Next most common is burnt and sticking contacts.

  • Less common are open circuit coils or failed joints.

The first two problems can often be fixed and the third rarely.

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Vibrator Unit

Oxidised Contacts:-  Even NOS vibrator units of this type tend to suffer from oxidised contacts. It is believed to be caused by the rubber used for sound deadening and shock absorption giving off fumes over time which react with the metal used for the contacts.   The oxide coating acts as an excellent insulator preventing the flow of current through the vibrator and preventing the vibrator unit from "starting".   The solution is fairly simple, the vibrator must be carefully opened using pliers to straighten out the crimped over base of the aluminium can of the vibrator until the base and mechanism of the vibrator can be removed.   Try not to damage the can too much as you will have to re-make the crimp when you have finished repairing the unit.
     
 

Vibrator removed from can

Burnishing tool

      Contacts

 
     
 
  • Carefully remove the vibrator mechanism from its protective can. 
  • The points can then be burnished using a contact burnishing tool until the oxide coating is removed.  
  • Next re-gap the contacts, a business card is about the right thickness.
  • Check vibrator now works and "sounds right".  If excess sparking from contacts or if unit sounds "rough" try re-setting the gap between contacts by opening or closing the gap slightly until the unit is working satisfactorily.  When the unit is working properly there should be little or no sparking visible at the contacts.

    Note; The process is somewhat subjective but after a bit of experimentation with setting the gap you should soon get the hang of it.  Be careful not to over bend the contact arms.  The use of a "stroking tool" as used to adjust relays is best, but the job can be done using long nose pliers.

     

  • If the vibrator is a spare and not expected to be used immediately lightly coat the contacts with a contact cleaner fluid suitable for electronic component contacts.  This should prevent or slow down oxidation reoccurring for a considerable time.  As soon as you use the vibrator the protective coating will be burnt away so do not re-test the vibrator before placing it into storage after applying the preservative coating.  
  • Re-fit the vibrator to its protective can and re-crimp the base.  Note;  Do not remove the rubber material from the can as it is important to damp down the noise and vibration of a working vibrator.
  • Job finished.
 
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  Burnt and pitted contacts:-   Is usually caused by the points operating out of sync, which may be caused by long usage or faulty circuitry in sets power supply.  Check set for faults before replacing vibrator. 

The vibrator points should be set up so that all four contacts have little if any sparking seen. This allows the primary & secondary of the vibrator transformer to operate efficiently.

Otherwise follow the procedure as set out above.

Notes:

  • Ensure pits and "whiskers" on contacts are removed by careful burnishing.  Be careful not to remove more contact material than necessary.
  • If contacts are welded together it may be possible to prize them apart but if not there is generally little you can do to save the unit.
  • Trying to make one good unit out of several dud units is generally not successful as usually the same bits are faulty.  Also experience has shown that working units should not be disassembled further than set out above as reassembly is fraught with difficulty and in Club members experience unlikely to be fully successful even if you manage to get it back together.
  • It also helps with regulation & vibrator "hash" if 1N4007 or similar diodes are fitted across the vibrator points on the vibrator socket.  Make sure the diodes are fitted the right way around though!
 
     
Open circuit coils or failed joints:-  If the coils in the unit are open circuit or have shorted turns there is normally little you can do.  Even if you are able to rewind the coils re-assembling all the disassembled bits to make a working unit is next to impossible.  However if the coils are OK re-soldering the pin connections on the base and other soldered joints may do the trick.
     
  Members of the ZC1 Club have successfully restored many faulty vibrator units using the above methods.  
     

top                                                                                         June 2011