Digital Board Removal - Keithley SourceMeter 3A 2420 Service Manual

3.
4. Remove analog board assembly.
5. Disassemble analog board assembly.
CAUTION
NOTE

Digital board removal

Perform the following steps to remove the digital board. This procedure assumes that the an-
alog board assembly is already removed.
NOTE
1.
2.
3.
4.
Remove screws.
• Remove the two fastening screws that secure the analog board assembly to the
chassis. These screws are located on the side of the board opposite from the heat sink.
• Remove the two screws that secure the heat sink to the chassis.
After all screws have been removed, carefully lift the analog board assembly free of the
main chassis.
• Remove the screws that secure the analog board and heat sink to the analog board
subchassis.
• Carefully remove the heat sink by sliding the clips off the power transistors.
Be careful not to damage the heat sink insulation layer.
• Remove the analog board from the subchassis.
• Remove the four screws that secure the bottom cover, then remove the cover
from the bottom of the PC board.
When re-installing the heat sink, make sure that all clips are properly installed
and centered on each pair of output transistors.
In order to remove the digital board, the display board must first be removed.
Remove the IEEE-488, Digital I/O, and RS-232 fasteners.
The IEEE-488, Digital I/O, and RS-232 connectors each have two nuts that secure the
connectors to the rear panel. Remove these nuts.
Remove the POWER switch rod.
At the switch, place the edge of a flat-blade screw driver in the notch on the pushrod.
Gently twist the screw driver while pulling the rod from the shaft.
Unplug cables:
• Unplug the display board ribbon cable.
• Unplug the cables going to the power supply.
• Unplug the rear panel power module cable.
• The fan may need to be removed.
Remove digital board.
Slide the digital board forward until it is free of the guide pins, then remove the board.
During re-assembly, replace the board, and start the IEEE-488, Digital I/O, and RS-232
connector nuts and the mounting screw. Tighten all the fasteners once they are all in
place and the board is correctly aligned.
Disassembly 5-5