Technical data

Troubleshooting
Hints
(continued)
Current input is inoperative
Verify that the rear panel 3 A, 250 V current fuse is functional.
Verify that the internal 7 A, 250 V high-interrupt fuse is functional.
Power supply problems
Check that the input to the supply voltage regulator is at least 1 V
greater than its output. Circuit failures can cause heavy supply loads
which may pull down the regulator output voltage.
Some circuits produce their own local power supplies from the main
supplies. Be sure to check that these local supplies are active.
In particular, the
ADC (analog-to-digital converter), ac, and front panel
sections have local supplies. Always check that the power supplies are
free of ac oscillations using an oscilloscope.
Failure of the analog voltage reference
U403 will cause many self-test
failures. Be certain that
U403 is seated properly in its socket.
Check the main supply voltages as shown below.
Readings indicate OVERLOAD
An overload is caused when the gain and offset corrected reading result
is greater than the full scale value (or less than the full scale value) for
the present measuring function and range. This can be caused by
incorrect calibration, saturated (railed) dc input amplifier, or by failure
of the a-to-d converter. Overload can also be caused if the current source
value is too large in the ohms function. In ac functions, overload will
also be generated if the output of the rms-to-dc converter
U308 is greater
than 2 Vdc for sinewave inputs > 20 Hz.
Power Supply Minimum Maximum
+5 Ground Ref.
+5 Floating
+18 Floating
-18 Floating
+7REF Floating
+5REF Floating
4.75 V
4.75 V
18.0 V
-17.0 V
6.45 V
4.75 V
5.25 V
5.25 V
20.0 V
-19.1 V
7.35 V
5.25 V
Chapter 6 Service
Troubleshooting Hints
118