First, ask neighbors if they have intercoms. This will allow us to locate the fault. If all the other intercoms operate properly, so the problem you have. Carefully inspect the cable going from apartment block to the hole in the wall through which he goes to the entrance. Perhaps his damage (breakage or short circuit) you will see with the naked eye. Repair it again and you will be able to use the intercom system. When all else fails, remove the residential unit cap and see how the inserted wires into the terminal block. If necessary, correct them and tighten the screws. In any case, do not move the jumper! Then assemble the block. Work in rubber gloves, in case of insulation breakdown in the Central power supply.
If the screen of the intercom, equipped with an optical keyboard, the message "E-2" and the keyboard does not work at all (app key reaction is normal), this means that the holes through which the light travels from the sensors to the sinks, clogged with dirt. Look closely at the frame of the keyboard, and you will find it of infrared emitters and photosensors. Gently swipe him a few times with a cloth to remove dirt. If soon message "E-2" will disappear and the keys will work, you just eliminated the problem.
There is a malfunction of the intercom, the perpetrator of which are the residents themselves. Wanting to eliminate the loud bangs when the door is closed, they are glued to the electromagnet duct tape or Scotch tape. As a result, the claps disappear, but sufficient force for opening locked doors, is greatly reduced, and to open it anyone can. Remove all such stickers from the electromagnet and the door stopped clapping, fix and adjust closer — in fact, he's the problem.
The rest of the fault side of the block to search for and eliminate prohibited, because it is not your property, and the property of the organization that supports the intercom. However, it is not possible, since the unit is attached to the door or rivets, or screws, which drilled the slot. The same applies to the cables located outside of the apartment. If the housing unit intercom combined with the housing of the alarm unit, to search for and troubleshoot and not in it. Find in the entrance of the advertisement with the telephone number of the organization that supports intercom and call of the master.