Lakeshore 642 User Manual page 100

Firmware Replacement (Continued)
4. Disconnect the ribbon cable to the Analog Board assembly from J-2.
5. Disconnect the cable to the fan from J-3.
6. Disconnect the ribbon cable to the Keypad Board assembly from J-4.
7. Disconnect the main transformer connector from J-7.
8. Remove all connections from the IEEE-488, RS232C, Power Supply, Auxiliary, and Magnet Water connectors on
the back of the Model 642.
9. Remove and retain the hexagonal mounting standoffs from the IEEE-488 and RS232C connectors on the back of the
Model 642.
10. Locate, remove and retain the two 6-32 pan-head machine screws holding the Digital Board in place. See Figure 7-6.
11. Remove the Digital Board by pulling it toward the front to clear the rear connectors from their back panel holes and
then carefully lifting the Board assembly out of the unit.
12. Locate the appropriate IC(s) on the main circuit board. See Figure 7-6. Note orientation of existing IC.
CAUTION: The ICs are Electrostatic Discharge Sensitive (ESDS) devices. Wear shock-proof wrist straps (resistor
limited to <5 mA) to prevent injury to service personnel and to avoid inducing an Electrostatic
Discharge (ESD) into the device.
13. Use IC puller to remove existing IC(s) from the socket.
14. Noting orientation of new IC(s), use an IC insertion tool to place new device(s) into socket(s). Ensure that no pins
are allowed to bend.
15. Reinstall the Digital Board into the unit taking care to properly locate the bottom edge of the board between the four
locator pins on the bottom of the instrument. Push the Digital Board carefully rearward taking care to locate the rear
connectors through the rear panel of the unit.
16. Attach the Digital Board using the two 6-32 pan-head Phillips screws removed earlier.
17. Remount the IEEE-488 and RS232C connectors using the hexagonal mounting standoffs removed earlier.
18. Reinstall all appropriate rear panel connections that were removed earlier. Take care NOT to interchange the
"Magnet" and "Power Supply" connectors.
19. Reinstall all Digital Board connections removed earlier. See Figure 7-6
20. Recheck that all connectors have been reinstalled and confirm proper locations and orientations of each.
21. Follow the top of enclosure installation procedure of Section 7.8.2.
7-8
Lake Shore Model 642 Electromagnet Power Supply User's Manual
Service