Introduction; Handling And Cleaning; Handling Pc Boards; Solder Repairs - Keithley 2750 Service Manual

5-2 Disassembly

Introduction

This section explains how to handle, clean, and disassemble the Model 2750. Disassembly
drawings are located at the end of this section.

Handling and cleaning

To avoid contaminating PC board traces with body oil or other foreign matter, avoid
touching the PC board traces while you are repairing the instrument. Some circuit board
areas, especially those under the motherboard shield, have high-impedance devices or sen-
sitive circuitry where contamination could cause degraded performance.

Handling PC boards

Observe the following precautions when handling PC boards:
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Solder repairs

Observe the following precautions when soldering a circuit board:
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Wear cotton gloves.
Only handle PC boards by the edges and shields.
Do not touch any board traces or components not associated with repair.
Do not touch areas adjacent to electrical contacts.
Use dry nitrogen gas to clean dust off PC boards.
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 area when you have finished the repair by using
pure water with clean, foam-tipped swabs or a clean, soft brush.
Once you have removed the flux, swab only the repair area with methanol, then
blow dry the board with dry nitrogen gas.
After cleaning, allow the board to dry in a 50°C, low-humidity environment for
several hours.
Model 2750 Multimeter/Switch System Service Manual