Scanning Auger Objective Coil Replacement Procedure

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This post describes the steps needed to successfully replace the objective coil on PHI 600 and 660 systems. Note: Use gloves, clean tools and place UHV aluminum foil on your workspace. For best results, dust off the assemblies with dry nitrogen or canned air as you reassemble the analyzer to remove any dust particles.

Tools required:

Latex gloves


Small screwdrivers

Tweezers and/or needle nose pliers

048-4 Bristol spline wrench

Disassembly Procedure

  1. Vent the system.
  2. Remove the filament housing (8″ flange on a hinge).
  3. Stand the analyzer on the back of the condenser nipple (8″ flange).
  4. Remove magnetic shield (4 screws).
  5. Remove conical ceramic (4 screws, aluminum ring).
  6. Remove the outer cylinder after first disconnecting the VM screw.
  7. Remove the upper inner cylinder assembly (4 screws). Be very careful not to touch the grids.
  8. Remove the 8 screws that hold the two aluminum rings in place and carefully lift up the Objective lens assembly. Scribe the objective lens assembly so that you can put it back with the exact same orientation.
  9. Turn the Objective lens housing upside down and remove the 8 screws that hold the nose cap in place.
  10. Hold the cap and point the lens assembly up and carefully lift the nose cap off.
  11. Carefully lift off the octopole ceramic and spacers. TIP: Position the spacers on the clean aluminum foil in the order in which you remove them so that you can replace them in the same order later.
  12. Remove the 3 flat spring couplers and ceramics from the objective coil wires. You will need a 0.048 4-spline wrench.
  13. Loosen and remove the 4 nuts which hold the objective coil to the base plate.
  14. Remove the objective coil. Note that there are 4 spacers on the studs.

Reassembly Procedure:

  1. Install the spacers on the objective coil studs and insert the objective coil into the base.
  2. Put the nuts on the studs and tighten the nuts finger tight.
  3. Using some 0.020 wire, slip it in and around the coil and the center tube so that the coil is evenly spaced around the center tube.
  4. Securely tighten the 4 nuts.
  5. Slide the ceramics over the objective wires and replace the 3 objective coil spring couplers.
  6. Stack up the octopole ceramic spacers and slide the octopole ceramic back on. It is keyed and can only go on one way.
  7. Carefully slide down the nose cap and replace the 8 screws finger tight.
  8. Slightly rotate the nose cap to make sure that the octopole ceramic is well seated and then tighten the 8 screws.
  9. Reinstall the objective lens assembly into the inner cylinder. It can only go in one way and still make the electrical connections.
  10. Install the two aluminum rings in place and tighten the 8 screws.
  11. Measure the resistance of the condenser and objective connectors and make sure that you have a good connection to the objective lens. The resistance on the two internal windings of the objective coil (Pins A, B and C) should be about 8 Ω each and 16 Ω across.
  12. Check for connectivity on pins A, B, C, D, E, F, G and H on the octopole deflection feedthrough to the octopole ceramic to ensure that you have a good contact on each plate. The best way to do this is to set your meter up so that it beeps with continuity and then insert a small (0.010) wire into the nose cap and move it around while having the other end of the meter connected to the octopole defection feedthrough. If the connections do not all check out then remove the objective lens assembly and look for a contact problem.
  13. Reinstall the upper inner cylinder assembly. (Do not touch the grids!)
  14. Install the outer cylinder and reattach the VM wire.
  15. Carefully place the conical ceramic on top of the outer cylinder and measure the resistance of the outer cylinder to ground. It should be 3 MΩ. If the conical ceramic is not making good contact, the resistance will be about 6 MΩ. It needs to be 3 MΩ. Shim with copper or gold foil if necessary. The resistance coating section (the dark sections between the rings) on the conical ceramic should be 180 degrees out from the resistance coating on the base.
  16. Replace the aluminum ring on top of the conical ceramic and tighten the 4 screws evenly and firmly (but not too tight!).
  17. Reinstall the magnetic shield.
  18. Degauss the analyzer.
  19. Ohm-out the objective connector one more time, and also ohm-out the VM to ground to ensure that the resistances are still correct.
  20. Use a new gasket and reinstall the CMA into the bell jar.
  21. Pump down the system and bake-out.

The pictures below will help you to understand this procedure.

RBD Instruments provides replacement objective coils for the PHI 600 and 660 scanning Auger systems. Contact us for more information. The coils are expensive but we occasionally have used coils that cost much less than a new one.

Additional information on the 25-120A CMA is posted below the pictures.


25-120A Analyzer Info

1. Resistance measurements:

  • Cond. coil, pins D & E, 10 ohms
  • Obj. coils, pins A, B, & C, 8 ohms, 16 ohms, open to ground

2. Steering – all pins open to ground

  • Cond. X: A & C, gnd at J
  • Cond. Y: B & D, gnd at M
  • Obj. X: E & G, gnd at L
  • Obj. Y: F & H, gnd at K

 20-622 System Test

It is possible for a 20-620 or 20-622 to work on the bench but not focus properly on a system. That is because on the bench the Objective and ISO Objective supplies are tested separately but on the system the objective coil is actually two coils which are tied together. It is possible for one of the objective supplies to cave in when connected to the objective coil. You can do a quick test by measuring the voltage across the current resistors behind the front panel of the 20-622 or 20-620.

Voltages for the 20-622 are listed below. The 20-620 should show a similar trend.

20-622 3kV Beam voltage, COND set to 35%, OBJ set to 74.49%, and Objective fine pot set to midrange. COND .856 V DC
OBJ 3.68  V DC
ISO OBJ 3.69  V DC

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