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SENTEX Spectrum Intercom Troubleshooting

Posted 07.16.09 at 04:11 PM by Zachariah Boren

I am here in Canoga Park, CA in the 818 area code and it split to 818/747. I had an older SENTEX Spectrum DI Intercom with a handsfree kit in a surface mount box. It was using a single analog phone line to dial each unit in the apartment building.

The problem was that the old 100 system board / bios memory chips only has 7digit phone number capability and we needed 11 digit dialing. EX: 1-(818)-xxx-xxxx , 1-(747)-xxx-xxxx. To fix this an order was made for SN1650055 Sentex 301 (Mic & Speaker) Kit.

After the new unit was installed and programmed via. computer using SVWin software and a modem I ran into a problem where the "#" key did not give me a dial tone. I instead got 4 beeps from the unit and a "b" in the LED indicator and no dial tone or option to type in a unit number.

The 'b' indicates that the system thinks that the phone line is busy. This can happen if the phone line measures other than 48vdc when it is idle, or if does not drop to between 5 to 7vdc when it goes off hook.

Testing the voltages I found that everything was fine yet the system still did not work. While troubleshooting In program mode 69+# gave me a dial tone used to adjust the speaker volume. The phone line was working as I could program the intercom via PC.

I hooked up a Tempo 77HP Tone Generator and sniffed out the telco line with a Tempo 200EP Amplifier Probe back at the punchdown box. It turned out that there was a inline testing block installed many years ago by the telco company that did not effect the old 100 board.

Once the punchdown testing block was removed, the intercom system operated normal.

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