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Wireless door bell Sender not working

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fixit7

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Diagnose circuit board issue

I am trying to diagnose why the door chime no longer works.

The receiving unit sounds the various melodies.

The battery voltage is ok.

I have thoroughly cleaned the circuit board.

The led lights up when the switch is pressed.

Any other things to try next?

Thanks.

https://imgur.com/a/cZH4n5U
 

betwixt

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Re: Diagnose circuit board issue

I'm guessing that is the remote sender board, it appears it isn't sending any RF signal or the receiver isn't picking it up. With only two units it can be difficult to tell which end is responsible, when you say the receiving unit sounds the melodies, how are you triggering them?

Brian.
 

fixit7

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Re: Diagnose circuit board issue

With a push button soldered into the circuit board.

The sender unit resides on my outside entry door.

I live about 1/4 mile from a lake that intermixes with the ocean if that may be a consideration.
 

fixit7

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Re: Diagnose circuit board issue

Why was my thread closed?

One person answered.

Maybe I am in the wrong place?
 

ads-ee

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Re: Diagnose circuit board issue

Your thread does not appear to be closed, but as a moderator sometimes it's difficult to tell what a normal user sees.
 

fixit7

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I have a wireless doorbell made by Radio Shack. :)

Something is wrong with the sender unit.

When the button is pressed, the led lights up but the chimes do not ring.

The chime unit does work, I believe, because it sounds when I change the melody.

I am wondering if it is worth the trouble to see what is wrong with the sender unit?

Thanks.

I forgot to mention, but I live within 1/2 mile of a lake that does have saltwater ingress.
 

Allen6502

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The Tx PCB looks fine to me. I normally would suspect a bad push button. But as you said the LED lights up OK, then it should be fine too.

The inductance are printed on the PCB and I couldn't find datasheet for MC908T and the SAW. Did you do a rough check on Q1 and Q2 BJT to make sure that they are not shorted?

Your PCB is attached here..
fmWEG5o.jpg

Another similar sender I found which is similar uses 433MHz frequency..
doorbell_433_4.jpg
 

fixit7

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Thanks for your reply.

I had a second transmitter and it worked fine with the receiving unit.

I suspect, but have no evidence, is that the first transmitter failed due to the high humidity environment of living 1/4 mile from a lake fed by saltwater.

I have a near constant breeze.

I may try to find a way to make the transmitter water proof or at least water resistant. :)
 

betwixt

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I live on the coast with constant seawater nearby and in an area of very high rainfall, I have never had problems with corrosion.

If the LED on the sender is coming on when you press the button, the fault almost certainly lies with the transmitter oscillator. That would be Q2 or a component connected to it. From tracing the tracks it appears the signal that turns the LED on is the same one that enables the oscillator (ASK mode) so if one works and not the other it implies the oscillator is at fault. You need an audible receiver, spectrum analyzer or a wide bandwidth oscilloscope to check the operation conclusively.

Brian.
 

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