Introduction; Repair Considerations; Power-On Self-Test - Keithley 2700 Service Manual

4-2 Troubleshooting

Introduction

This section of the manual will assist you in troubleshooting and repairing the Model 2700.
Included are self-tests, test procedures, troubleshooting tables, and circuit descriptions. 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 procedures in Section 5 and
the parts lists in Section 6 for further information.
WARNING

Repair considerations

Before making any repairs to the Model 2700, be sure to read the following considerations.
CAUTION
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Power-on self-test

During the power-on sequence, the Model 2700 will perform a checksum test on its EPROM
(U156 and U157) and test its RAM (U151 and U152). If one of these tests fails, the instrument
will lock up.
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 hazardous
voltages.
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.
Without 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 instruc-
tions for the Model 2700 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 pre-
cautions and cleaning procedures explained in Section 5.
Many CMOS devices are installed in the Model 2700. 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 2700 must
be recalibrated. See Section 2 for details on calibrating the unit.