If any part of the self test fails, the display will stop and indicate "FAILED" after the
appropriate test. The display does not proceed to the display of VDU emulations. The front
panel LED display also stops. This indicates a fault that cannot be remedied. Please contact
Black Box for assistance.
Back-To-Back Testing
It is possible to test a pair of multiplexers in a back-to-back mode. This is a useful way to
gain familiarity with the configuration procedures, and to check for correct operation if
malfunction is suspected.
To carry out a back to back test a multiplexer pair are interconnected via the composite
connector using the appropriate cable selected from Appendix G.
Our normal procedure is to use the X.21/V.11 composite back-to-back cable with the
interface selection also set to X.21/V.11.
When connected by the cable one multiplexer is selected to Internal Clock and the data rate
set to an appropriate value (64Kbps.) The second multiplexer is selected to AUTO or EXT
thus accepting clock from the other.
When correctly interconnected and appropriate clocking is accepted the multiplexer pair will
intercommunicate as if a link was present; CARRIER is then indicated as PRESENT on the
VDU, with the CARRIER LED being illuminated.
Having achieved this situation all configuration procedures may be exercised.
After back-to-back testing it is essential to reconfigure the composite clocking, from internal
(INT) to external (EXT or AUTO,) on the unit originally providing a system clock.
