12V Door Bell System Repair

[JimKnopf92]

Hello,

I was hoping I could get some advice from a knowledgable person here

We have a 12V door bell system installed in our communal tenement. Exactly this one: UK Door Bell, Model 801, Issue 6A
In this video the guy takes it apart and explains it, it is spot on:

Recently our buzzing signal has died down to a short blip or is simply not working at all. There have been no changes made to the system (it is correctly wired).
https://www.bellsystem.co.uk/assets/(pd-083-iss-3a)-bellcall-manual.pdf

I suspected the microcontroller that makes the Dinglinglingling sound was broken and replaced the handset. But the result is the same:
- intercom, speaking and hearing downstairs: works
- door opener button: works
- door bell: does not work/only comes though as short blip sometimes

I have measured the following:
Power supply at handset: 13V
Power for signal when door bell is rung 7-6V - I suspect this is too low and does not allow for a loud long lasting door ringing?

I went to the distribution box on my level for the signals and measured there - same Voltagelevels.

I also rung had my wife ring my neighbour while measuring at this distribution box (he has the same door bell system) and his got ~12V and the door bell made the full long loud sound it should.

I am not sure what to make out of this but assume the following. (could you comment or confirm?)

1. our transformer for the power supply works fine (system has 13V and neighbour's doorbells can ring)
2. When my door bell gets rung the handset only receives a signal of ~7V, so there must be too high resistance in the line between the actual ring button in the door bell panel downstairs and my handset?

Does that makes sense? What could I do to confirm/fix?

Sidenote: We got a new entry door installed (but kept using the old unlocking buzzer magnet, because the new one was not working).
Something like this https://www.elro.eu/en/electric-door-opener-12v-dl6000 (it only received ~8V at the door, which I assume was too little to trigger the magnet to pull the blocking bar down, I tested it at 12V with a transformer and it worked; the old one was operating at 8V)

 

[sparkymarka]

Post picture of external panel ….could be a faulty / corroded button

 

[JimKnopf92]

I am honestly not sure how to get inside there. As you can see there are 2 rivets. How do I get it off the wall?

Any idea? Also just to understand what to expect... is the transformer behind there, so will there be 230V cabling? I tried finding example pictures online but wasn't able to... if you have any that would be helpful.

 

[sparkymarka]

Ok that’s OLD …. They are probably star torx that are worn , would probably say it’s the button that’s high resistance / corroded only way to check would be remove your call wire on the back of the panel and touch it on the common rail ( this is all 12v ac or dc )

 

[sparkymarka]

Example ( old aiphone panel ) see how there is a common wire to all buttons ( these can be removed and replaced ) also bell wiring diagram

 

[Harry Bloomfield]

I am honestly not sure how to get inside there. As you can see there are 2 rivets.

Those rivets, are some sort of heavily corroded security screw. You will need to drill the heads of those, and take the remains to a nut and bolt stockist, to try to source some sort of replacement.