Leak Checking

• RGA should not have com cable plugged in without power cable plugged in. Don't just unplug power cable.

• Always turn the electron multiplier on!

• Work top-to-bottom (helium rises, so start on the top of the machine first to avoid false positives)

• Bagging flanges can be helpful.

  • Small leaks can take time to appear, but blowing helium all over the lab can lead to false positives (e.g. helium diffuses through the lab to the flange that is actually leaking)

• Sometimes bisection method is easier than brute-force for pesky leaks, e.g. bag top half of machine; if on top half, then bag source flange; if not on source flange, bag CAR; continue as-needed.

• Viton seals, outlet of scrolls, etc. can all look like leaks.

• Tabulated from Homan's spreadsheet

  • More here: http://webbook.nist.gov/chemistry/mw-ser.html

  • Or here: http://sdbs.riodb.aist.go.jp/sdbs/cgi-bin/cre_index.cgi

• Example of how to interpret spectra: https://www.lesker.com/newweb/technical_info/vacuumtech/rga_03_simpleinterpret.cfm

• Cracking patterns often available in the built-in SRS RGA software

• Isotope proportions for all the elements are at

-SRB: I tried nesting tables to make it more intuitive to edit, but there were issues...

Last updated by SDM - June 2016

1. Partial pressure readings during an analog scan do not make sense, e.g. values are too high or the ratio for certain peaks do not make sense

2. RGA is reading negative values and wildly varying values during leak checking

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Broken analog scan

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Broken leak check

Sending the RGA to SRS costs ~$650 to replace a resistor and a transistor, which cost ~$1 alone and require ~15 minutes of soldering.

• Parts that you need to complete this repair can be purchased from Mouser, Allied Electronics, Digitkey, etc, but I'll give the Mouser links below

  • 1x 100 ohm carbon film, 1/4 Watt, 5% tolerance length ~ 6 mm (http://www.mouser.com/Search/ProductDetail.aspx?R=CF1%2f4C101Jvirtualkey66000000virtualkey660-CF1%2f4C101J)

  • 1x npn transistor, part # D44VH10G (part number is independent of saler), TO-220 (TAB) package type, with a through hole (http://www.mouser.com/Search/ProductDetail.aspx?R=D44VH10Gvirtualkey58410000virtualkey863-D44VH10G )

    • The RGA manual says it's just D44VH10, but that part contains lead and is no longer fabricated, but D44VH10G is the lead-free version

• Remove the outer cover of the ECU box (top and bottom) and disconnect the power cable between the two halves

• Remove the big threads (long rods) that normally screw into RGA flange when attached to the machine

  • Remove c-clips, washer, and rod on both sides (top and bottom)

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Removing C-clamp and long rod

• Remove the back plate

  • Fan screws

  • RS232 screws

  • Power pin screws

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Removing back plate

• Remove the bottom side PCB (i.e. not the resistor board -- i.e. the board with the femail RS232 and the red and green LEDs). You'll need to remove two screws from the side of the box before you can pull up this board.

  • After unscrewing, gently pry up the board. It is held on the the rest of the box assembly with delicate pins. You also risk cracking the board if you warp it too much

• Remove the resistor R408

  • Cut wires at the resistor base. There are 2 to cut.

  • Using solder, heat the hold near the old resistor's wire ends that were just snipped, and pull the wire ends from the board

  • Clean the remaining solder from the holes on the board

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Resistor R408

• Remove the npn bipolar transistor Q401

  • Cut wires at the transistor's base. There are 3 to cut.

  • (From the outside of the box) unscrew the nut that holds the transistor to the box

  • Remove the remaining pins you just snipped and clean the holes of the remaining solder

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Transistor Q401

• Add the new resistor and transistor

  • Note: one of the RGAs has a wire near the transistor because there is a problem with the connection to pin 1 of the transistor. Add a wire to another appropriate node in the circuit, e.g. the node that connects to C402 or R405.

  • Consult the manual if you need more information about the circuit and board

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Circuit layout

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Board layout

• Perform a continuity check after completing the solder of the new components to ensure the circuit was correctly reconnected

• Reassemble the board and box

  • Screw in the transistor

  • Add the plastic slab, then the bottom PCB that was removed -- be gentle!

  • Add the back plate

  • Add the long rods with c-claps and washers

  • Add the outer covers of the box

• Check the rebuilt RGA against another known-good RGA in the lab by performing an analog scan of the known-good RGA, then the repaired RGA.

  • E.g. compare the peak values to make sure the repaired RGA is performing correctly.