Lakeshore Learning Materials 642 - Manual (Page 99)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
Service 7-7
7.7.2 Handling Electrostatic Discharge Sensitive Components
Observe all precautions necessary to prevent damage to ESDS components before attempting installation. Bring the
device and everything that contacts it to ground potential by providing a conductive surface and discharge paths. As a
minimum, observe these precautions:
1. De-energize or disconnect all power and signal sources and loads used with unit.
2. Place unit on a grounded conductive work surface.
3. Ground the technician through a conductive wrist strap (or other device) using 1 M
Ω series resistor to protect
operator.
4. Ground any tools, such as soldering equipment, that will contact unit. Contact with operator's hands provides a
sufficient ground for tools that are otherwise electrically isolated.
5. Place ESDS devices and assemblies removed from a unit on a conductive work surface or in a conductive container.
An operator inserting or removing a device or assembly from a container must maintain contact with a conductive
portion of the container. Use only plastic bags approved for storage of ESD material.
6. Do not handle ESDS devices unnecessarily or remove from the packages until actually used or tested.
7.8 ENCLOSURE TOP PANEL REMOVAL AND REPLACEMENT
WARNING: To avoid potentially lethal shocks, set current output to 0 A, turn off the power supply, and disconnect
it from AC power line before performing this procedure. Only qualified personnel should perform this
procedure.
7.8.1 Removal
1. Set power switch to Off (O) and disconnect power cord from the power outlet.
2. Remove the Model 642 from rack (if necessary) to gain easy access to the top panel.
3. Remove and retain the 17 flat-head Phillips screws securing the top panel of the Model 642.
4. Remove and retain the two truss-head Phillips screws and nylon washers from the top edge of the front panel that
secure the top panel to the front panel.
5. Carefully remove the top panel from the unit.
7.8.2 Installation
1. Replace the top panel on the Model 642 with the folded lip of the panel toward the front of the unit.
2. Replace and secure the 17 flat-headed Phillips screws. Do not use excessive torque.
3. Replace the two Phillips head screws securing the top panel lip to the top edge of the front panel.
4. Replace the Model 642 in the rack (if used)
5. Reconnect the Model 642 to the power outlet. Apply power via the front panel button (l).
7.9 FIRMWARE REPLACEMENT
There are two integrated circuits (IC) that may potentially require replacement. See Figure 7-6 for respective locations.
• Main Firmware Erasable Programmable Read Only Memory (EPROM) (U35) – Contains the user interface software.
Has a sticker on top labeled “MModel 642F.HEX” and a date.
• DAC Microcontroller (U51) – Contains software that controls the output DAC. Has a sticker on top labeled “MModel
642DACF.HEX” and a date.
Use the following procedure to replace either or both of these ICs.
1. Follow the top of enclosure removal procedure of Section 7.8.1.
2. Refer to Figure 7-5 and locate the Digital Board assembly.
3. Disconnect the housekeeping transformer connector from J-1.