How Do I Troubleshoot a Multiplexer Problem?
Models 570 & 575
These 2 units are very similar and can be tested individually or as a system. Make sure you have a terminal and a properly pinned cable to connect to one of the ports of the Mux.
1 - As a quick check, set the front panel switch to Local Loopback. All LEDS except the Power LED should be "OFF."
2 - If any other LED is "ON" or blinking, the unit is defective.
3 - Connect a terminal to one port of the Mux and start typing on the keyboard, the TD & RD Leds should blink and the characters should appear on the terminal screen.
4 - The test above checks everything internal except the output circuitry. For a complete check of the unit, set the Local Loopback switch back to normal and jumper T+ to R+ and T- to R- on the green link connector on the back of the unit.
5 - Repeat step 3. Repeat this for the second unit.
6 - If the individual units test good, then reconnect them as a system. Disconnect all cables from the ports. All LEDS should be "OFF" except the power LED. If any of the LEDS are "ON" or blinking this normally means that your link cable is defective or the twisted pairs are not paired properly, T+ & T- have to be one twisted pair and R+ & R- the other. The T+ lead must connect to R+ and T- to R- and vice versa. This problem can also be caused by having a stub somewhere on the line. If this link line is going through punch down blocks you may have a pair of wires connected inadvertently going nowhere.
7 - This problem can also be caused by the NORMAL/HALF SPEED switch internal in the Model 570 set opposite in each unit. This switch must be set the same in both units. This switch allows the units to communicate at longer distances (8000 feet rather than 5000 feet) but at a maximum of 9600 Baud instead of 19.2 KBPS.
8 - The Muxes have no settings for Baud rate, etc., they are transparent to these parameters but the equipment connected to the ports at each end must be set the same per port.
Back Panel RJ-12 pinout for the Multiplexers
Note 1 - DI,CI,DO & CO, the I and O refers to Input and Output with respect to the Mux. DATA IN TO MUX & DATA OUT FROM MUX, also CONTRO IN TO MUX AND CONTROL OUT FROM MUX
Note 2 - The +12 volts pin is voltage available but normally not used.
