Lexicon MPX 110, Service Manual, Page: 16 / 75

MPX 110 Service Manual
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6. Turn VARIATION to 13 and press Store to set up the MPX 110 for the following tests.
GAIN TEST
This test verifies the input-to-output gain characteristic of the MPX 110 through the signal path.
1. Apply a 1kHz signal at 775mV to the MPX 110.
2. Verify 1.95 V +/- 0.05V at the MPX 110 Left output.
3. Connect the oscillator output to the MPX 110 Right input.
4. Connect the analyzer input to the MPX 110 Right output.
5. Verify an output of 1.95V +/- 0.05V at the MPX 110 Right output.
SIGNAL-TO-NOISE TEST
This test checks the signal-to-noise through the MPX 110 signal path.
1. Set the scale on the distortion analyzer to measure -50dBu signal.
2. Disconnect the oscillator from the MPX 110 input, or turn the oscillator off.
3. Verify that the noise floor is <90dBr.
4. Connect the oscillator output to the MPX 110 Left input.
5. Connect the analyzer input to the MPX 110 Left output.
6. Repeat the test, verifying the levels at the Left output.
THD+N
This test verifies THD+N through the MPX 110 signal path.
1. Apply a 1kHz signal at 220mV to the MPX 110 left input.
2. Adjust the scale on the distortion analyzer to measure % THD+N.
3. Verify a distortion level <0.05% THD+N at the Left output.
4. Connect the oscillator output to the MPX 110 right input.
5. Connect the analyzer input to the MPX 110 right output.
6. Verify a distortion level <0.05% THD+N at the right output.
FREQUENCY RESPONSE TEST
This test verifies the frequency response of the MPX 110 through the signal path at 20Hz, 3kHz, 5kHz, and
20kHz.
1. Apply a 220mV signal at 1kHz with the analyzer Bandwidth filters off to the MPX 110 Right input.
2. Use the output level at the MPX 110 Right output for the 0DB reference to check frequency response.
3. Verify that the signal level output is within ±0.5dB of the reference at the above frequencies.
4. Connect the oscillator output to the MPX 110 Left input.
5. Connect the analyzer input to the MPX 110 Left output.
6. Repeat the test, verifying levels for the MPX 110 Left output.