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No Phase Lock


The lock light starts to blink on the front panel... Now what?!

The lock light monitors the most critical circuits of the unit. Check the unit in the following order:

     1.  Make sure the lock knob is fully ccw and the variable gen is off.
     2.  Remove the case and observe the high loop and low loop LED's on               the modules. If only the low loop LED is lit, the problem is in the low loop. If the high loop LED is lit, the problem could be in the high loop, Dual VCO, Hi/Lo Filter, Low Pass Filter, or SMB RF connections that connect the modules together. Otherwise, the high loop is not calibrated correctly. If both LED's are lit, a time piece failure has most likely occured (TCXO or related area).
      The high loop circuit which includes the VCO, Hi/Lo filter and Low pass filter, is a very delicate circuit. At times it could function intermittently -- it might work for 30 minutes, lose phase lock, then work again. It is possible that it loses lock at one end of the spectrum only. If you are unable to calibrate the high loop to where it will stay locked all the time, it may be time to get your service monitor checked. Very few techs survive their first high loop/VCO experience. Of course this depends on your level, you make the call. Go to the Quick Cal section on this page to check out the High loop circuit.

      If you find the low loop light on, you can just send in the module for repair

High Loop Calibration

This is a quick check to see if your unit will stay phase-locked. A more detailed procedure is done upon thorough check of the modules.

  1. Set unit to 000.0000MHZ and adjust R60 until you are able to just barely lock up the unit. Then adjust slightly more then STOP.
  2. Set unit to 999.9999MHZ and adjust R61 in the same way as step 1.
  3. Hi/Lo filter R65 is the next adjustment. The filter is located at the bottom of the unit, right behind the front panel, with 2 rf lines and a brown wire attached to it. There is also a number on this filter. Write the number down. This is the crossover frequency and you need to subtract 90 from this number.
  4. Attach a dvm voltmeter to the brown wire on the Hi/Lo filter and set freq to 400MHZ. The voltmeter should read approximately +10 volts.
  5. Slowly increase frequency until your voltmeter reads -10 volts.
  6. Is the reading +/- 10 mhz from the number that you wrote down after subtracting 90 from it? If not, start this process over and adjust R65 until it is.
  7. Gain adjustment R45. Set the unit to 50.04 MHZ and inject a 50 mhz signal at -30db.
  8. Set the IFR spectrum analyzer to 10Khz/div.
  9. Adjust R45 so the hump between the red lines is 4 to 8db. If the gain is set to high, oscillations will occur.
  10. R32 500khz null adjustment. This is not important for phase lock, but it should be adjusted if you see a 500khz dispersion off of the carrier. To eliminate this, adjust accordingly while monitoring the output with a spectrum analyzer.
High Loop Quick Cal