6-88
5. If one channel shows PASS flags on all the ATTEN tests, swap the Preamps between channels to
determine if the Preamplifier inputs are ok. If that swaps the problem, replace the faulty Preamp. If
the problem remains in the same channel, replace the defective Attenuator.
50mV
0.5
V
5V
2 mV to 50 mV
100 mV to 500 mV
1 V to 5 V
Signal
Out
VOLTS/DIV
50 mV
50 mV
50 mV
Signal In
ATTENUATOR CHECK
4. Connect the output of a Standard Amplitude Calibrator to the vertical input of the failing channel
using coaxial cable with no terminator. Set the Standard Amplitude Generator output and the
VOLTS/DIV setting on the 2430 to the values given in the following table and check the signal
path between the Attenuator and the Preamplifier input of the failed channel. With a 10X probe on
the test scope, view the signal at the Preamp input pin. Use NOISE REJ Trigger Coupling and
20 MHz Bandwidth on the test scope to clear up the trace noise and obtain a stable trigger. If only
one channel is bad, the other channel of the 2430 may be used to view the signal. The signal
amplitude out of the Attenuator and into the Preamp should be approximately 50 mV peak-to-peak
for each attenuator setting in the three ranges. A possible, but unlikely, source of a failure that is
not in the signal path between the Attenuator and the Preamp is a shorted capacitor (C414 or
C311) connecting to the Attenuator.
3. If one and only one audible click was heard for each of the first four front-panel changes above,
then the circuitry that drives the four mag-latch relays in each attenuator is functioning properly by
switching the individual relays to the opposite latched position (the audible click).
2. Check that one audible click is heard when changing the VOLTS/DIV setting between 50 mV and
100 mV (10X attenuation) and between 500 mV and 1 V (100X attenuation). Also check that one
audible click is heard when changing the Vertical input coupling between DC and AC, and when
turning the fifty ohm input ON and OFF. Several clicks will normally be heard when switching in
and out of GND Coupling.
1. Check that the correct test voltages are used for the ATTEN calibration step.
Troubleshooting Procedure:
THIS TEST IS ONLY PERFORMED USING EXTENDED CALIBRATION. With the Preamplifier set to
50 mV non-inverted, the Preamplifier gain test is repeated interactively using standard dc test voltages
applied to the CH 1 and CH 2 inputs. By adjusting the Preamplifier balance to give - 2 divisions, the
output is swung between -2 (input grounded), and +2 (input set to 0.2 V per div), divisions. The gain
control DAC is adjusted to achieve an output within specifications. The difference between the resulting
control DAC setting and the gain calibration constant measured at 50 mV per division (non-inverted) is
the attenuator gain constant. If a solution cannot be found, or if the resulting solution is more than a
2% gain error, the test result is set to FAIL. If the test fails, an attenuator gain of 0 (nominal) is stored
for the calibration constant under the assumption that the test setup may be in error. The test is
repeated for all three vertical attenuators (1X, 10X, and 100X) using input test voltages of 0.2 Vdc,
2 Vdc, and 20 Vdc.
Testing Method:
Channel 1 and Channel 2 Attenuators AT400 and AT300 (schematic diagram 9):8700
ATTENUATORS
Table 6-6 (cont)
Maintenance-2430 Service
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