Agilent Technologies 5975T LTM GC/MSD, Troubleshooting And Maintenance Manual

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Electronics
14
Troubleshooting and Maintenance Guide 223
MSD Power Supplies
Low voltage (AC-DC) MSD power supply
The low voltage MSD power supply is mounted next to the MSD
toroid transformer in the MSD electronics module. A universal
input power supply, it converts AC line voltage into the DC
voltages used by the rest of the electronics. The power supply
generates the following DC voltages:
• +24 V (nominal)
• +15 V (nominal)
• –15 V (nominal)
• +5 V (nominal)
High voltage (HED) power supply
The high voltage power supply provides the –10,000 volts DC for
the high energy dynode (HED) in the detector for the EI MSD.
The HED power supply also provides 600 VDC for the detector
focus lens. Due to the high impedance of this circuit, measuring
the detector focus voltage with a handheld voltmeter will give a
typical reading of 90 to 100 volts where the polarity matches
that of the HED voltage.
MSD toroid transformer
The MSD toroid transformer is mounted next to the AC board. It
provides 24 VAC for the mass filter and source heater circuits.
The input wires take 120 VAC or 200 to 260 VAC from the AC
board. The AC board samples the line voltage and uses a relay to
appropriately strap the toroid primary. The output wires
connect to the main board.