Problem with Audio on DP

[Warby]

HI

We are using a Fermax doorphone with a DPM. Everything works fine except for the audio, nothing can be heard either way. The D8 LED comes on when i press 0 for doorstatioin. It is not working on the phones or the Keypad.

The DPM ID is 1 (SW all shunted) and there are no other DP\'s. We are using a third party transformer for the Fermax unit and all cabling is in order.

The system is Comfort II .

Any Ideas?

[admin]

Perhaps the mic and speaker wiring to the Fermax side is reversed?
Or the Mic and Spk pair which are supposed to be connected to Comfort are connected to Fermax and vice versa?

[Warby]

I have tried reversing all the Mic Voice cables, DPM to comfort then Fermax to DPM.

 

[admin]

Which Fermax model are you using, is it the Cityline?
Some intercoms, not Fermax as far as we know require the \"handset\" to be offhook in order for the audio to go through This requires a relay to connect to the intercom side to give the offhook connection. This is why I asked for the model

Do you have access to a multimeter or better still an oscilloscope?
Are you able to see if there is AC Voltage at the SPK out to Fermax  terminal block when the door station should be talking? If you can see AC volateg here then the problem is related to the Fermax connections

[Warby]

 

We used a tone source genarator and wand to narrow it down to the Fermax unit.

We tried reversing the polarity of the DC input which has solved it.

Thanks for the quick responses!!