Keithley 2750, Service Manual

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4-2 Troubleshooting Model 2750 Multimeter/Switch System Service Manual
Introduction
This section of the manual will assist you in troubleshooting and repairing the Model
2750. Included are self-tests, test procedures, troubleshooting tables, and circuit descrip-
tions. It is left to the discretion of the repair technician to select the appropriate tests and
documentation needed to troubleshoot the instrument. Refer to the disassembly proce-
dures in
Section 5 and the parts lists in Section 6 for further information.
WARNING The information in this section is intended only for qualified service per-
sonnel. Do not perform these procedures unless you are qualified to do so.
Some of these procedures may expose you to hazardous voltages that
could cause personal injury or death. Use caution when working with haz-
ardous voltages.
The metal shield located on the motherboard is at analog LO potential and
may have hazardous voltages. To avoid a possible shock hazard, connect
the metal shield to chassis ground before servicing.
Repair considerations
Before making any repairs to the Model 2750, be sure to read the following
considerations.
CAUTION The PC boards are built using surface mount techniques and require spe-
cialized equipment and skills for repair. If you are not equipped and/or
qualified, it is strongly recommended that you send the unit back to the
factory for repairs or limit repairs to the PC board replacement level. With-
out proper equipment and training, you could damage a PC board beyond
repair.
• Repairs will require various degrees of disassembly. However, it is recommended
that the Front Panel Tests be performed prior to any disassembly. The disassembly
instructions for the Model 2750 are contained in
Section 5 of this manual.
• Do not make repairs to surface mount PC boards unless equipped and qualified to
do so (see previous CAUTION).
• When working inside the unit and replacing parts, be sure to adhere to the handling
precautions and cleaning procedures explained in
Section 5 .
• Many CMOS devices are installed in the Model 2750. These static-sensitive
devices require special handling as explained in
Section 5 .
• Whenever a circuit board is removed or a component is replaced, the Model 2750
must be recalibrated. See
Section 2 for details on calibrating the unit.