Panasonic KX-TD500 System Reference Manual page 1456

3.35 Digital trunk failure (out of synchronization)
Error Code
Possible cause of
the malfunction
Countermeasures
Note
70xx xx=01 to 40 : Slot number
T-1/E-1 card (physical number xx) lost the synchronization with the clock time
sent from the Central Office.
Confirm that the setting of "Frame Sequence" and "Line
Coding" are matched with that of the leased lines.
If not, change the setting of your KX-TD500 and CUS.
Then check the clock mode.
Check the cabling between "T-1/E-1 and "CSU and "CSU
and NIU". If not properly cabled, change and cabling.
Execute Loopback Test(Internal).
Test Results NG
Replace the T-1/E-1
card with a new one.
Execute Loopback Test(External: between KX-TD500 and
CSU)
OK
Check the CSU. If not good, replace it with a new one.
Ask the T-1/E-1 carrier to check the line conditions.
Or, check the equipment in other switching system which
your T-1/E-1 lines are connected with.
Another T-1/E-1 card with next priority will work as a master card, if more than
two T-1/E-1 cards were registered to system by CLP command beforehand.
Otherwise, the system will synchronize with the system internal clock.
15-E-38
OK
NG
OK
NG
Test Results
OK
NG
NG
End
OK