Keithley 2750, Service Manual

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5-4 Disassembly Model 2750 Multimeter/Switch System Service Manual
Disassembly procedures
Case cover removal
Follow the steps below to remove the case cover to gain access to internal parts.
WARNING Before removing the case cover, disconnect the line cord and any test leads
from the instrument.
1. Remove Screws — Remove the four screws (two on each side) that secure the case
to the chassis.
2. Remove Cover — To remove the case, grasp the case at the sides, and carefully
slide the cover back about an inch, then lift the case cover off the chassis.
Motherboard removal
Perform the following steps to remove the motherboard. This procedure assumes that the
case cover is already removed.
1. Remove the IEEE-488, RS-232, and Digital I/O fasteners.
2. The IEEE-488, RS-232, and Digital I/O connectors each have two nuts that secure
the connectors to the rear panel. Remove these nuts.
3. Remove the front/rear switch rod.
4. At the switch, place the edge of a flat-blade screwdriver in the notch on the push-
rod. Gently twist the screwdriver while pulling the rod from the shaft.
5. Unplug cables:
• Unplug the display board ribbon cable from connector J1014.
• Unplug the transformer cables from connectors J1002 and J1003.
• Unplug scanner slots ribbon cables from connectors J1012 and J1016.
• Unplug analog backplane connections J1008 and J1010.
• Unplug front panel input terminals connector from J1017.
6. Remove the fastening screws (five total) that secure the motherboard to the chassis.
Most screws are around the periphery of the board (one of these screws secures
U144), while two are located away from the edges of the board.
7. During reassembly, replace the board, and start the IEEE-488, RS-232, and Digital
I/O connector nuts and the mounting screw. Tighten all the fasteners once they are
all in place and the board is correctly aligned.
8. Remove the motherboard by sliding it forward until the connectors clear the rear
panel, then carefully pull the motherboard from the chassis.