Keithley 7999-4, Инструкция по эксплуатации

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Service Information 4-5
Replacing components
Replacement parts
Replacement parts can be obtained directly from Keithley Instruments, Inc. See the parts list
in Section 5 for part numbers.
Replacement precautions
CAUTION Observe the following precautions when replacing components:
• To avoid contamination, which could degrade switch performance,
always handle the switch only by the covers and side edges. Do not
touch the connector, board surfaces, or components on the switch.
• Use care when removing components from the PC board to avoid pull-
ing traces away from the circuit board. Before attempting to remove a
relay, use an appropriate de-soldering tool, to clear each mounting
hole completely free of solder.
Soldering considerations
When using solder on the circuit board, observe the following precautions:
• Use an OA-based (organic activated) flux, and take care not to spread the flux to other
areas of the circuit board.
• Remove the flux from the work areas when the repair has been completed. Use pure
water along with clean cotton swabs or a clean soft brush to remove the flux.
• Once the flux has been removed, swab only the repaired area with methanol, then blow
dry the board with dry nitrogen gas.
• After cleaning, allow the card to dry in a 50˚C low-humidity environment for several
hours before use.
Disassembly
Perform the following steps to disassemble the Model 7999-4 to gain access to parts on the
circuit board:
1. Remove the six screws that hold the case together and the two hex-nuts on the DB9
connector.
2. Separate the two halves of the case.
3. Unplug the connector from the relay.
4. Remove the screws that secure the PC board to the case, then remove the board.