There is a test for the MLX phones. Also, have you checked the wiring and cords? anyone of those items could cause a similar problem. Here is an excerpt from the Legend R6.0 Maintenance & Troubleshooting document starting on page 88:
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MLX Telephone Tests
If the LEDs, ringer, buttons, switchhook, or display appear not to be working, try the steps below.
1. Pick up the handset.
2. When you hear dial tone, press *00 (the feature access code).
The telephone enters test mode. For some tests, this means the LEDs
turn on; for others, it means the phone starts ringing.
• This test connects a test tone to the B-channel and sends a
repeated ring burst to the telephone.
• On an MLX telephone with a DSS attached, all LEDs light and the
phone rings throughout the test.
• On an MLX display telephone, the display blanks out and is
replaced with a grid of small dots.
3. Press each line/feature button (two LEDs each).
The red and green LEDs should toggle on and off.
4. Press each fixed-feature button that has an LED (Feature, HFAI,
Mute, and Speaker).
Each LED should toggle on and off.
NOTE:
Mute and Speaker LEDs may not toggle consistently because they
are managed by the control unit and the telephone.
5. Press each fixed-feature button that does not have an LED
(Transfer, Conf, Drop, and Hold) and each dialpad button.
When you press each one of these buttons, the Message LED should
toggle on and off.
6. Press the fixed-feature buttons and the dialpad buttons in the order shown below to turn on all the LEDs.
a Volume down
b Volume up
c Transfer
d Conf
e Drop
f Hold
g Dial 123456789*0#
The LEDs should toggle on and off.
7. If the MLX telephone does not have a display, hang up and go to
Step 9; if it does, continue with the next step.
8. To test an MLX display, press each display button.
Each button name should display in the upper-left corner as described in Table 3–2.
9. If any of these tests fail, replace the MLX telephone.
10. Test the Multi-Function Module (MFM) if present.
a Connect a single-line telephone to the MFM.
b Pick up the handset on the single-line telephone.
c When you hear the system access or intercom dial tone, dial *09
from the single-line telephone.
This connects the diagnostic test tone to the B-channel.
d Dial 123456789*0#; wait for silence, and then quickly press the
Recall button to perform a switchhook flash. You should hear a confirmation tone (three beeps).
e Hang up.
You should hear a ring burst, and the Message LED should turn on.
f Dial #54 to turn off the Message LED and resume normal
operations.
11. If these tests fail, replace the MFM.
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....JIM....