User's Manual

144
Modem 34336
Appendix D: Jumpers
WARNING
Jumpers should be switched only by qualified service personel.
For most applications, there is no need to reset the modem’s internal jumper
switches. However, a jumper switch will have to be reset if you need to do any
of the following:
• Connect frame ground to signal ground.
• Switch from A/A1 control to MI/MIC control.
• Strap the modem for use in a DC rack enclosure.
• Change the function of EIA interface pin 25.
If you need to reset a jumper switch, refer to the next page to determine the
jumper that should be switched, where it is located, and how it should be set.
The jumpers are numbered on the circuit board; for example, JP4 is jumper
4. To access the jumpers, unscrew the four screws on the bottom of the
modem and carefully lift off the cover.
WARNING
Improper setting of AC and DC power jumpers could result in serious
damage to the modem.