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Mass Spectrometer Maintenance
Replacing the Diffusion Pump Thermocouple Gauge
The thermocouple gauge will need replacing if its filament has burned out or its
thermocouple has become detached. This will be indicated in the Diagnostics
report. To replace the thermocouple gauge:
1. Turn off the MS as described in the Start-up and Shutdown section.
2. Carefully separate the MS from the GC by approximately 250 mm (10").
NOTE: Be careful not to break the GC column.
3. Remove the top cover.
4. Remove the transfer line.
5. Rotate the MS to give full accessibility to the left side.
6. Remove the four screws holding the left side cover in place, and remove the
cover.
7. Disconnect the manifold and trap heater cables and move out of the way.
8. Remove the Peltier baffle ducting by pulling up at the front and sliding forward.
9. Disconnect the Peltier baffle power leads (orange and yellow wires) from the
Peltier baffle and slide out of the way.
10. Remove the two screws holding the Peltier baffle duct base to the rear panel,
and remove base by pulling up and forward over the Peltier baffle heat sink.
11. Disconnect the thermocouple gauge cable from the thermocouple gauge.
12. Unscrew the plastic nut and slide it up the 1/8" pneumatics exhaust tube.
Withdraw the tube from the elbow, using a twisting motion.
13. At the rear of the instrument, loosen the clamp holding the vacuum tubing onto
the stainless steel elbow, and withdraw the tubing. Slightly twisting the tube
while withdrawing may help.
14. Remove the small clamp from the diffusion pump’s exhaust port by unscrewing
the red wing nut, removing the screw, turning the clamp so the open end faces
the diffusion pump, and pulling the clamp toward you.
15. Lift the elbow up and wiggle it free of the rear panel.
16. Clamp the elbow in a vice fitted with jaw protectors.
17. Unscrew the thermocouple gauge using a 9/16" open-ended wrench.
18. Wrap three to four turns of Teflon
tape clockwise around the threads of the new
gauge (27-229907-00).
19. Check and remove residual Teflon tape from thermocouple gauge port.
20. Screw the thermocouple gauge into the threaded port on the elbow until snug.
21. Remove and inspect the seal on the diffusion pump exhaust port
(27-402536-00).
Replace if it is worn or damaged
.
22. Wipe the seal clean with a lint free cloth, and refit to the exhaust port.
23. Guide the tube end of the elbow through the hole in the rear panel, and wriggle it
into position on the diffusion pump exhaust port.
Take care not to dislodge the
seal.