Pulsing noise in the phone speakers?

Audioguru again

Joined Oct 21, 2019
3,318
Hee, hee. My Name Brand 4k UHD TV is 11 months old, still covered by its warranty and has a turning on problem that I phoned customer support about. They told me how to do a system reset which fixed the problem but the problem came back. I phoned again and they said to send them photos of the problem which I did. I asked if there is a local repair depot and they said no.

They said to take the TV to the local garbage recycling depot and throw it away there, and send photos of it in the trash, then they will give my money back.

It seems that it is made so cheaply that some of them are garbage.
 

djsfantasi

Joined Apr 11, 2010
7,763
I had a problem with an air conditioner. The manufacturer had me cut off the power cord and send it to them. When they received it, they shipped me a new unit. No AC for a couple more days, but whatever...
 

Thread Starter

xchcui

Joined May 12, 2014
203
Yes,i got the idea of your examples,but if i wanted to return the phone,
as anniel747 suggested,i would already be doing that and i could take the money back or replace it.
It is funny to get that kind of advice,it is an obvious option,but don't get
me wrong,i don't underestimate any advice and i grateful for any help.
I asked those questions in this forum in order to understand the problem
and learn new things that i couldn't find other place.
I will very appreciate,Audioguru,if you may answer my last question.
You says that in the old phone,the hook switch disconnects its DC parts from
the phone line,besides the ringer.In the modern phone,does the hook switch
also disconnects its DC parts from the phone line,while only the lcd screen
and its ringer gets power or there are other components that gets power?
 

Audioguru again

Joined Oct 21, 2019
3,318
The LCD display in a phone might be disconnected when it is on-hook if the display is not showing the time like a clock.
The mechanical bell in an old phone and is capacitor-coupled when on-hook therefore it draws no DC current if the capacitor does not leak DC current.

The ringer IC in a modern phone has an input coupling capacitor that might leak a DC current of 20uA when not ringing and the phone is on-hook.
 

Thread Starter

xchcui

Joined May 12, 2014
203
The LCD display in a phone might be disconnected when it is on-hook if the display is not showing the time like a clock.
The mechanical bell in an old phone and is capacitor-coupled when on-hook therefore it draws no DC current if the capacitor does not leak DC current.

The ringer IC in a modern phone has an input coupling capacitor that might leak a DC current of 20uA when not ringing and the phone is on-hook.
In my case,the lcd is not disconnected when it is on-hook,but
even if it was disconnected,the circuit inside the telephone
should continue to work in order to keep the date/clock update,shouldn't it?Aren't there some component,like Integral-Circuit chips
,inside the phone that are still working when the phone is on-hook
in order to keep things update etc.?
 

Thread Starter

xchcui

Joined May 12, 2014
203
Why are you asking US about YOUR phone that we have never seen?
Have you never seen a corded phone with lcd and speaker phones?
Are one is so different from another?
As you may see,my last question was a kind of a general question about those kind of modern corded phones,which have lcd screen and speakerphones.
It is not necessarily have to be my specific one.
The question may be a little exceeding from the main issue,
but since we talked about the consumption on-hook and you said that
it should not consume current on-hook,i was interesting how it can be,
if the phone still needs to keep the clock and date update.
So i tried to figure out what components in those kind of phones
consume power when the phone on-hook.
You said that you opened a lot of telephones,so i realized that i can
trust your knowledge.If you don't know,it's okay.
I didn't forget that you helped me so far with all my questions.
Thanks.
 

Audioguru again

Joined Oct 21, 2019
3,318
I have a worn out corded speakerphone with LCD screen made by Thompson and one I use everyday made by Uniden. They both have very different circuits and both use four AA battery cells for the display and for the speakerphone audio amplifier.
 

Thread Starter

xchcui

Joined May 12, 2014
203
I have a worn out corded speakerphone with LCD screen made by Thompson and one I use everyday made by Uniden. They both have very different circuits and both use four AA battery cells for the display and for the speakerphone audio amplifier.
I thought that it was obvious,but maybe,i should have mentioned
,that the phone doesn't runon batteries.It gets its power only from the telephone line.
I am sure that each phone may have a different circuit,but
the idea is the same idea,if both phones have the same functions.
So,on modern phones that have phone speakers and lcd screen
and powered only by telephone line voltage,doesn't the
phone still consume power while it on-hook?what electronic components
consume power in that case?
Thanks.
 

Wolframore

Joined Jan 21, 2019
2,317
I recall hearing pulsing on old analog phones when my cell phone was about to ring. Some sounds systems used to do that. It could be radio interference from unbalanced lines and poor design.
 

Thread Starter

xchcui

Joined May 12, 2014
203
...On modern phones that have phone speakers and lcd screen
and powered only by telephone line voltage,with no batteries,but
the date/clock is showing all the time on lcd display even when on-hook,
Doesn't the phone still consume power while it on-hook?what electronic components
consume power in that case?
Thanks.
Audioguru again,from your experience,may you answer
to my question?
Thank.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
3,318
I took apart my worn out Thompson speakerphone. It uses four AA batteries to power its display and speakerphone.
It does not have a clock so it draws no current when it is on-hook.
Its speakerphone circuit is a "black blob" on a separate little pcb.
Its speakerphone is powered by batteries so that it is loud enough even when the telephone switching center is far away which might be the problem with your pulsing speakerphone.

Since your phone has a clock on its LCD screen when on hook and has no batteries then guess what powers the clock. The telephone line or simple magic? Unplug it from the telephone line to see if its LCD clock still works for a day or two.
 

Thread Starter

xchcui

Joined May 12, 2014
203
I took apart my worn out Thompson speakerphone. It uses four AA batteries to power its display and speakerphone.
It does not have a clock so it draws no current when it is on-hook.
Its speakerphone circuit is a "black blob" on a separate little pcb.
Its speakerphone is powered by batteries so that it is loud enough even when the telephone switching center is far away which might be the problem with your pulsing speakerphone.

Since your phone has a clock on its LCD screen when on hook and has no batteries then guess what powers the clock. The telephone line or simple magic? Unplug it from the telephone line to see if its LCD clock still works for a day or two.
I tend to believe that it is a Christmas miracle :)
Yes,the lcd clock gets its power from the telephone line
and if i unplug it for more than few seconds,the time and date
are lost and resets to default value.
So,the 25uA that i measured before,when the phone is on-hook,
doesn't necessarily a coupling capacitor leakage.does it?
It is a normal consumption of the lcd clock/date time isn't it?
 
Last edited:

Thread Starter

xchcui

Joined May 12, 2014
203
I wonder if your cheap Chinese phone is illegally stealing power from the phone company for its LCD clock? My Name-brand phones do not.
At my previous post,it wasn't a statement(refer to the cause of the
on-hook current),it was a question.
So,from your answer can i conclude that the only components
that powered when the phone is on-hook are the lcd display and
its corresponding chip,while 25uA current is normal for this consumption?
 
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