Hi, I'm having a problem with a 7890A/5975C GC/MS, it rebooted and now I get a banner that says "STATUS - Not ready Oven off AUX HEATER 2 FAULT".
I would like to know what this sign could be due to, if it is something related to connectivity, software or if it was suddenly the mainboad.

  • Aux 2 Heater Fault.  Aux 2 is nearly always setup for the MSD transferline heater/sensor.  See: 5975 Series MSD Troubleshooting and Maintenance Manual, starting on Page 153.

    From the computer, set the MS to vent. When the vent cycle is complete, don't let air in, just turn the GC and MS power off. 

    If it's possible and you're very careful, without removing the column, pull the MSD very slightly away from the GC -watching that you do not stretch or break the GC column - until you can see the wires/connector for the transferline heater/sensor.   If it's not possible without damaging the column, remove the column from the already vented MS, then pull the MSD away to gain access to this connector.

    Unplug that connector, as shown in the red below.

    Turn on the GC power...does it give that same error on the GC display?   If it does, either Aux 2 is something else or the main board has troubles..   

    If the error does not show up on the GC display, then take a voltmeter, set it to Ohms, and measure these resistances at the connector that goes to the MSD transferline.

    Two of the wires are skinny and two are fatter and the pairs are diagonal from each other.

    Measure between connectors where the two skinny wires go - it should read about 109 Ohms at room temperature.

    Measure between connectors where the two fatter wires go - it should read about 16 to 17 Ohms at room temperature.

    If either are open, shorted, or measure dramatically differently, the heater/sensor must be replaced.

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