Door entry
Voice intercom and door-opening system
A typical block entry system for flats. It has four functions :
- Entrance door button to sound a buzzer in one individual flat
- Entrance door-lock release. A common line so the lock can be opened from any flat
- Speech from a microphone in the entrance panel that can be heard in any handset speaker
- Speech from any handset microphone heard from a speaker in the entrance panel.
1980's-era typical system description
The enrty-phone is a white plastic wall-hung handset like a telephone. Lifting the handset releases an off-hook switch which makes the microphone and speaker live and you can then talk to anyone outside. You can also speak to anyone else with an off-hook handset. There may be an amplifier in the system or it may be just a signal voltage generated by a carbon microphone and heard in a sensitive speaker. All that would need to work is a small direct current (DC) voltage to energise the microphone.
The buzzer and lock circuit is separate and runs on alternating current (AC) low voltage and it's the 50Hertz buzz you can hear at both.
Often the entry panel has back-lighting for the call buttons, this is also run from low-voltage AC.
The handset is hard-wired through a multicore telephone-type cable having 5-6-8 strands, usually in colour coded pairs e.g. blue/white + white/blue, same for orange, green, brown. Looking at a compatability chart on a supplier's website, there is no common use of numbering or colouring between manufacturers.
Circuit diagrams
In general, five wires go to the handset from the entry panel. Ring - Talk - Common - Hear - Unlock. Common is from the positive + side of the power supply so The RING wire will only show a voltage when the entry button is pressed and -12V will appear across the buzzer terminals. The other side of the buzzer is the common terminal. The door-open button on the handset also connects to the common one and pressing this will drop the voltage on the UNLOCK terminal and so identify itself. Knowing those three terminals, the other two are Talk and Receive. and the R will make a scratching in the speaker if you disconnect and reconnect its wire. That should give you the connections.
Complications come with wire duplication, usually more than one common wire. Some handsets have 4 wires, 2 for T and 2 for R. Also cables come in twisted pairs, so 5 connections on six wires means a redundant common wire to the entrance. There are also options for additional functions, like a button to turn on the stair-lights.
Comparing two handsets I've seen, one had a MUTE function where the hook-switch decoupled the speaker wires 2 and 6, while the other didn't and the hand-held unit had a push-to-talk button instead.
The hook switch is half-depressed when the hand-piece is stowed. When fully depressed it connects the metal strips between 9 and 6, Before pressing, you should find a voltage reading across 9-6 of -12VAC.
... to be continued. Any info gratefully received!
Trouble-shooting
Try this link
https://doorentrydirect.com/acrobat/bell/data/Bell%20801%20Trouble%20shooting.pdf
Video Doorbells
... to be added?