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I live in a very old house. Up until recently, my doorbell worked fine, but at some point in the last couple months it stopped working. At the transformer, I see ~18V, so that appears to be ok, but it is what I see at the chime that has me a little confused.

The previous chime had three unlabeled wires run to it. My working assumption is that 1 is to the transformer, 2 goes to the front door and 3 may have run to another switch (but I don't know where this is/was). This is where I have become stumped: At the chime, if I measure between 1 (the transformer wire) and either of the others, I read ~8V. I get this reading whether the front door switch is opened or closed (I took the button off and have tested Voltage with them loose and also tied together). Can anyone help me with a likely explanation for this? As I said before, the system was working up until recently.

  • Is this a total of 6 conductors (2 per wire)? I assumed so until you said you measured between '1 and..' implying a single conductor. Either way I'd start by making note of how it's wired now, then disconnecting everything and trying to label it. Check for voltage first (to identify the transformer). If you get 0V, switch to continuity mode and watch while someone pushes the doorbell, you should be able to identify the doorbell wire that way. If you don't know where the other wire goes, don't connect it. – gregmac Mar 13 '17 at 21:40
  • Most of the old ones I have worked on had 2 chimes and a common 1 chime for the front door one for the back door. I thought they were 24v. If you have voltage check that the switch is good these are very cheap and fail more often than the transformers do. The voltage was supplied to each chime through the switches. – Ed Beal Mar 13 '17 at 21:55
  • Doorbells usually fail because the pushbutton corrodes out due to the elements. If the button is mounted on the door itself, the second most common failure is fatigue in the wire where it bends at the door hinge point. – Trevor_G Mar 13 '17 at 22:39
  • My main question is: what could the explanation be if I have left the front door switch open (removed button, disconnecting leads) and at the chime, I still measure 8V between the transformer lead and and either of the other two. I will try @gregmac's suggestion of using continuity mode to find out which of the other leads it to the front door, but I don't understand why I'd still be measuring 8V with that switch open. – sethro Mar 13 '17 at 23:49
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Most likely, the doorbell button has failed.

There will always be voltage across the doorbell button unless it is pushed. That's because the circuit would be complete, but for the button. I would expect to see 18 volts (or bare transformer voltage), but with an electronic chime, I could see that value being a little funny.

You can test this out; short the 2 wires to the doorbell, that is the same as ringing the doorbell.

  • Thanks for the reply, but I should have been more clear in my question. I removed the chime, and the front door button. Even with the two button leads disconnected and not touching, I read 8V between the transformer wire and either of the other two wires where the chime had been connected. – sethro Mar 13 '17 at 23:42
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    Oh. That sounds like the classic "induced voltage" (really capacitive coupling) from parallel mains wires. They can produce phantom voltages as high as 80% of mains voltage if they run right alongside for some distance. Any load at all, even the jeweled needle mechanism on a classic analog voltmeter, will make it go away. Modern DVM's have too light a touch. – Harper Mar 14 '17 at 0:41
  • OK, so if I understand, you're saying that is a red herring? I definitely think these wires are being run together for a significant distance. – sethro Mar 14 '17 at 0:46
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    Yes. That red-herring regularly appears on this forum, and drives us bonkers. You can test it definitely by putting a very small resistor load on it (my "go-to" for a small resistive load is an incandescent bulb like a night-light; given the low voltage perhaps a larger one like a 40W.) – Harper Mar 14 '17 at 0:48
  • Thank you much! I was so confused by this. Now that I'm not distracted by this, hopefully I'll be able to find the actual problem. If you make this "induced voltage" an answer, I'll accept it. – sethro Mar 14 '17 at 0:49

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