This isn't a question, but my experience might be useful for others.
My daughter's flat has a phone entry system, and the amplifier went wrong. It's a Bell Model 61, like this:-
https://doorentrydirect.com/bell-61-2-way-speaker-unit-with-volume-control
I bought a replacement and that works, but I thought that I might as well find out what had gone wrong, so I opened it up. It is incredibly old-fashioned and simple for something that is over £50 delivered.
The screw terminal connector had corroded and I couldn't unscrew one of them, so I had to replace the block. However, that didn't stop the intercom from working. I hadn't cleaned up the pads from unsoldering before I took the photos.
The middle terminal comes from the microphones of any of the phones that have been picked up, so usually only one when working. That connection is pulled up by R9 from about 9 V, regulated by the TIP110. The audio is taken though the board on the through-plated hole near the microphone, and along the track on the top to another hole and C10.
The through-plated hole near the microphone had corroded through. I fixed that with bit of wire soldered through the hole. There's no real waterproofing of the housing and it's outside in the rain. The part of the board near the connectors has been wet, and the failure point was the bit that was wet, and had a DC bias on it for a decade.
I'm putting this here in case anyone else wants to try fixing one. I guess that most entry phone systems are the responsibility of a landlord, who gets someone in.
My daughter's flat has a phone entry system, and the amplifier went wrong. It's a Bell Model 61, like this:-
https://doorentrydirect.com/bell-61-2-way-speaker-unit-with-volume-control
I bought a replacement and that works, but I thought that I might as well find out what had gone wrong, so I opened it up. It is incredibly old-fashioned and simple for something that is over £50 delivered.
The screw terminal connector had corroded and I couldn't unscrew one of them, so I had to replace the block. However, that didn't stop the intercom from working. I hadn't cleaned up the pads from unsoldering before I took the photos.
The middle terminal comes from the microphones of any of the phones that have been picked up, so usually only one when working. That connection is pulled up by R9 from about 9 V, regulated by the TIP110. The audio is taken though the board on the through-plated hole near the microphone, and along the track on the top to another hole and C10.
The through-plated hole near the microphone had corroded through. I fixed that with bit of wire soldered through the hole. There's no real waterproofing of the housing and it's outside in the rain. The part of the board near the connectors has been wet, and the failure point was the bit that was wet, and had a DC bias on it for a decade.
I'm putting this here in case anyone else wants to try fixing one. I guess that most entry phone systems are the responsibility of a landlord, who gets someone in.
