MAINTENANCE
Section 17, Page 25 May 2002
MECHANICAL ADJUSTMENT OF CRYSTALS
There is rarely a need to mechanically adjust Crystal Oscillators. Always attempt to adjust
Crystal Oscillators electronically first (Section 6.2). If mechanical adjustment is necessary,
begin with adjusting the crystal on the XMT.
NOTE: It is always best to contact a Zonge engineer before attempting to perform mechanical
adjustments.
Mechanical adjustment of the XMT-32 crystal
After both the receiver and transmitter controller have had power applied for at least 60 minutes,
the following procedure can be used to adjust the mechanical trim on the crystals:
1. Set the 20-turn crystal adjust trim pot on the XMT to its mid point (turn the slotted screw
20 complete turns in one direction, then turn the screw 10 complete turns in the opposite
direction). This provides for the maximum electrical adjustment range after the
mechanical adjustment is made.
2. Turn the Power switch on the XMT to OFF.
3. Loosen the 4 hand screws on the right side of the front panel and remove the battery.
4. Remove the 6 screws holding down the left front panel and carefully lift it and the
attached boards out of the case.
5. Locate the crystal and the mechanical adjustment access hole cover.
6. Using a small flat-bladed screwdriver, carefully remove the adjustment hole screw
located in the middle of the base of the crystal (located next to the coaxial output
connector).
7. Attach the battery and turn the Power switch to the ON position. Wait at least 15 minutes
for the crystal to warm up again.
8. Connect the synchronization cable between the GDP-32
II
and the XMT-32.
9. Set the BATT/PHASE switch on the XMT-32 to PHASE, and observe the motion in the
meter due to the frequency differences between the crystals.
10. Use the plastic trim tool supplied with the GDP-32
II
to adjust the mechanical trim pot
inside the crystal can. Very carefully rotate the pot about 1/4 turn in one direction and
then the other to determine which direction it should be turned to bring the two crystals
into synchronization.
11. Adjust the mechanical trim to stop the motion in the phase meter. This should never take
more than 1/2 turn in either direction. If more rotation is needed, it could indicate that
you have a faulty crystal in either the GDP-32
II
or the XMT-32.
12. Wait for about one minute to determine that the adjustment is stable. If movement in the
phase meter resumes, very carefully adjust the mechanical trim to stop the motion.
13. TURN THE POWER SWITCH TO OFF, replace the screw covering the adjustment hole,
and put the XMT-32 back together again.
14. Turn the Power switch to ON and wait for 10 minutes before attempting to synchronize
the two units again.
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