Keithley SourceMeter 3A 2420, Service Manual

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4-2 Troubleshooting
Introduction
This section of the manual will assist you in troubleshooting and repairing the Model 2420.
Included are self-tests, test procedures, troubleshooting tables, and circuit descriptions. Note
that disassembly instructions are located in Section 5, and component layout drawings are at the
end of Section 6.
WARNING The information in this section is intended for qualified service personnel
only. 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.
Repair considerations
Before making any repairs to the Model 2420, be sure to read the following considerations.
CAUTION The PC-boards are built using surface mount techniques and require special-
ized 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 re-
pairs 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 2420 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 2420. 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 2420 must
be recalibrated. See Section 2 for details on calibrating the unit.
Power-on self-test
During the power-on sequence, the Model 2420 will perform a checksum test on its EPROM
and test its RAM. If one of these tests fails, the instrument will lock up.