This procedure will explain how to replace the channel plates (technically, they are Chevron plates) in the MCD detector used on Physical Electronics (PHI) 5600, 5700 and 5800 X-ray Photoelectron spectrometers. You may also want to check out our blog post on checking the MCD pins continuity.
Set up a work area with some aluminum foil and lint free cloths.
Vent the system.
Mark the MCD feedthrough flange to confirm the orientation of the flange when you replace it later.
Remove most of the bolts and nuts that secure the MCD feedthrough flange to the analyzer. The MCD feedthrough flange has some springs on the inside so there will be some tension when you remove the flange. There are 3 studs that are used to guide the MCD feedthrough flange when it is removed or installed.
Remove the last few nuts or bolts and carefully lower the MCD feedthrough flange and place it on the aluminum foil. Incidentally, most food grade aluminum foil has oil on it. If possible, use UHV compatible foil when working with electron optics.
The MCD assembly is located inside the 6″ CF flange where you just removed the MCD feedthrough flange from. You can remove one of the analyzer braces in order to gain better access to the MCD assembly.
At this point put on a pair of gloves as you will be working inside the analyzer and want to prevent oil contaminator from your hands. Use tools that have been cleaned with Isopropanol or Methanol.
Remove the screw that holds the capacitor in place.
Remove the capacitor by pulling on the pin that is connected to the MCD assembly. Do not pull on the capacitor. The pin wire is silver soldered to the capacitor and it can come off easily, so be very careful with the capacitor.
Remove the POS and NEG pins from the MCD assembly. Just pull up on the pins, keep the wires attached to the SHV feedthrough pins.
The MCD assembly is held in place with 2 slotted screws. Remove one of the screws completely. Be careful as it is easy to drop.
Loosen the second screw and then reach up and hold the MCD assembly as you remove the screw. Ease the MCD assembly down and out of the 6″ CF flange.
Set the MCD assembly on a clean working surface.
Pull up on the pins and insert a small Allen wrench or rod to hold the pins in place. The pins are spring loaded and by inserting a small Allen wrench or rod into the holes in the pins, that will prevent the pins from contacting the plates or 16 channel ceramic when replacing the plates.
Remove the two inner slotted screws.
Hold the MCD assembly as you rotate it 180 degrees so that the grid screen is facing up.
Remove the grid screen. Set it to the side.
Remove the ceramic. Set it next to the grid screen. As you remove parts, set them down next to each other in sequence. That will make it easier to reassembly the parts in the correct order.
Remove the gold spacer. Sometimes that part will stick to the bottom of the ceramic.
Remove the Teflon tubes
Remove the top plate.
Remove the second plate. Note that the plates have a little dot on them. Those dots need to face each other. So, the bottom plate has the dot facing up, and the top plate has the dot facing down.
Use some clean air or nitrogen to blow off the 16 channel ceramic. Feel free to dust off the MCD assembly and plates frequently. Dust is to be avoided as much as possible.
Install the new bottom plate. It sits on the gold spacer which is on top of the 16-pin ceramic. The hole in the plate needs to line up with the pin. The pin is centered in the hole in the plate. The little dot on the plate needs to face up.
Install the new top plate. The dot needs to face down and the pin should be centered in the hole in the plate.
Install the gold spacer. The tab on the spacer should be above the pin.
Install the Teflon tubes.
Install the ceramic over the Teflon tubes. The top of the tubes should be flush with the ceramic.
Set the grid screen on top of the ceramic.
While holding the grid screen and ceramic in place, rotate the MCD assembly 180 degrees so that the pins face up. Since the screw are not get installed, the only thing holding the grin screen and ceramic in place is you.
Install the two screws to secure the grid screen. You may need to rotate things just a little bit. Tighten the screws firmly but not too tightly or you may crack the ceramic.
Remove the Allen wrench or rods from the pins. Rotate the pins a little bit to make sure that they are seated.
Measure the resistance between the POS and NEG pins. You should have 15 to 24 meg ohms. From the other pin to POS or NEG should be about 1 Meg ohm.
The MCD assembly is now ready to install back into the analyzer.
Before you insert the MCD assembly, prepare one of the screws for mounting. A pronged grabber works well as does a starter screw driver. In a pinch you can use a regular screw driver with a little bit of tape to hold the screw on. The tape needs to stick to the screwdriver so that it all comes out when you remove the screwdriver.
Insert the MCD assembly (it can only go in one way or else the screw will not line up) and rotate it slightly to make sure that it is seated properly. Tighten the one screw to where it is just snug.
Install the second screw and tighten it to where it is just snug.
Slightly rotate the MCD assembly to make sure that it is seated properly and then tighten both screws firmly.
Reconnect the POS and NEG pins. Refer to the drawing to make sure that you do not insert the pins backwards. Also make sure that the POS and NEG wires are centered as the MCD feedthrough flange will need to clear the POS and NEG pins.
Insert the capacitor pin. Be careful not to stress the capacitor.
Reattach the capacitor wire screw and tighten the screw. The capacitor should be perpendicular (not tilted) as the MCD feedthrough flange will need to clear it.
Remove the used 6″ copper gasket.
Install a new 6″ copper gasket on the MCD feedthrough flange.
Carefully line up the MCD feedthrough flange and slide it onto the 3 guide studs. Install the 3 nuts to hold the MCD feedthrough flange in place and then slightly rotate the flange to make sure it is seated. The springs on the MCD feedthrough flange fit into the 16 holes in the MCD ceramic and press against the metal discs which in turn make contact with small capacitors inside the MCD assembly.
Install the bolts and lightly tighten the MCD feedthrough flange.
Measure the capacitance of all of the pins on the MCD feedthrough with respect to the vacuum chamber. The four center pins should read approximately 100 pf (open). All of the other pins should read 250 to 300 pf. If not, you need to drop the MCD feedthrough flange down and inspect to see where it is hanging up. Sometimes the spring pins do make contact with the MCD assembly and need to be adjusted slightly.
Once you have the correct capacitance on all of the pins, tighten all of the nuts and bolts.
The vacuum chamber is ready to pump down and baked.
Note: Set the MCD multiplier voltage to 1800V in the software so that after the bake out you start outgassing the new plates at a lower operating voltage.
Here is a side view of the MCD assembly.