220 5977B Series MSD Troubleshooting and Maintenance Manual
8 Electronics
Power Supplies
Low voltage (AC-DC) power supply
The low voltage power supply is mounted next to the toroid transformer in the
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 V DC for the high energy
dynode (HED) in the detector for the EI MSD. The EI/PCI/NCI MSD requires a
bipolar power supply that can also provide +10,000 V for NCI operation. 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 V where the
polarity matches that of the HED voltage.
Toro id tr ansf orm e r
The 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.
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