Telephone Disconects on First Ring

[WayneSallee.com]

My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the ring.
What usualy causes this? so that I can fix it.

Wayne Sallee
[email protected]

 

[WayneSallee.com]

And it is the phone, not the phone line shorting out.

I've already fully tested that.

Wayne Sallee
[email protected]

 

[[email protected]]

Is it only this phone? Have you tried a different phone?

Richard

 

[Fred McKenzie]

<< My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the ring.
What usualy causes this? so that I can fix i >>

Wayne-

The ringing voltage from the phone company is about 90 volts peak-to-peak,
probably a square wave. There is a DC voltage on the line from batteries at
the phone company, often 48 volts DC positive ground.

From your brief description, it sounds like something in the phone can't
withstand the peak voltage and breaks down. When that happens, the phone
company's equipment senses the DC current and reacts as if the phone had been
answered. However, when the ringing stops, the weak part stops conducting as
if the phone had been hung-up.

It is possible that the phone was damaged by lightning striking a telephone
pole. Look for burnt spots on the phone's circuit board. There may be a diode
bridge used to ensure correct voltage polarity, that has a bad diode. There
may be a capacitor across the line that has too low a breakdown voltage.
Unless you can isolate the weak part(s), a new phone is in order.

Fred

 

[Dbowey]

Wayne posted:

<< My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the ring.
What usualy causes this? so that I can fix it.

Many things can cause it, including telco trouble.

The first thing you should look at on your side of the Network Interface is:
How many ringer equivalents (REN) do you have on the line? Too many can trip
the ring, especially if you are on a long line from the Central Office.

Don

 

[w_tom]

Others here have provided good reasons for your failure.
Now start by breaking the problem into parts. Take a simple
POTS phone to your NID. Open that 'premise interface' box.
Unplug the wire going inside your house. Connect phone
directly to that box. Conduct the ringing test. Now we have
important facts to further solve the problem.

 

[[email protected]]

<< My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the
ring.
What usualy causes this? so that I can fix it.


Many things can cause it, including telco trouble.

To protect the telcos apparatus the telco usually
has a ring trip, so if the relatively high 50v ring
voltage meets a low impedance, it trips.
Try a single different phone directly on the
telcos incoming line socket.

 

[WayneSallee.com]

Thanks for your responce. That's basicly the way I see it. I have not been able
to find anything. I was hoping that there might be some part that was more
likely to be the defective item. I did try disconecting one part that shorts
the two lines. It seemed to work for a while, and then started doing it again.
It's kindof speratic.. The pice I disconected, I then reconected. It looks
like a light bulb, probably designed for filtering out high voltage. Since I
could not find anything obvious, I was hoping that there might be some common
culprit.

The problem with buying a new phone is that they just don't make them like this
one anymore. It's sad how manufacturers will add new features, but take out
good features.

I supose I could get a schematic and check all the points, but I doubt that
Panasonic still has the schematics for this phone.


Wayne Sallee
[email protected]

In a message dated 1/5/2005 1:19:16 PM Eastern Standard Time, [email protected]
writes:



Wayne-

The ringing voltage from the phone company is about 90 volts peak-to-peak,
probably a square wave. There is a DC voltage on the line from batteries at
the phone company, often 48 volts DC positive ground.

From your brief description, it sounds like something in the phone can't
withstand the peak voltage and breaks down. When that happens, the phone
company's equipment senses the DC current and reacts as if the phone had been
answered. However, when the ringing stops, the weak part stops conducting as
if the phone had been hung-up.

It is possible that the phone was damaged by lightning striking a telephone
pole. Look for burnt spots on the phone's circuit board. There may be a diode
bridge used to ensure correct voltage polarity, that has a bad diode. There
may be a capacitor across the line that has too low a breakdown voltage.
Unless you can isolate the weak part(s), a new phone is in order.

Fred

 

[Franc Zabkar]

My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the ring.
What usualy causes this? so that I can fix it.

Most (?) telephones have a bridge rectifier on the tip and ring inputs
to protect them from polarity reversals. This bridge could be made
from discrete diodes. In normal operation only two of these diodes (A
and D) are forward biased. It could be that one of these normally
forward biased diodes (eg diode A) is shorted. This would mean that
the phone would work OK when making calls (DC current) but not when
the line is ringing (AC current). During the negative AC cycle the
defective diode A would form a S/C with diode C.

A
Tip o-|-|-|>|---|-o +
| |
| B |
|-|<|-| |
| |
|--|>|--)-|
| C |
| |
Ring o-|--|<|--|---o -
D


- Franc Zabkar

 

[Franc Zabkar]

My telephone disconects on the first ring.
Sometimes it's the second or third ring, but it's shorting out on the ring.
What usualy causes this? so that I can fix it.

Disable your phone's ringer circuit by desoldering one pin of the 1uF
or 0.47uF 250VAC cap in that area. Call the phone using your mobile.
You won't hear it ring, but if your phone stays alive, then the
problem is somewhere in its ringer circuit, probably a "ring detect"
IC. These ICs contain the bridge rectifier alluded to in my other
post.


- Franc Zabkar

 

[[email protected]]

AOL is really getting discusting. My postings have not been properly
coming through lately. So I had to come to google to read the posts.

But anyway enouph about pathetic aol:

I tryed the REN factor by diconecting other lines to reduce the REN.
But sill it's the phone. When the phone does it speraticaly, it makes
testig more dificult. The speraticness is probably caused by capasitors
charching or discharging, making a slight difference in how the phone
hadles the situation.

Wayne Sallee
[email protected]

 

[[email protected]]

I've already done all that.

Wayne Sallee
[email protected]

 

[[email protected]]

What's the best way to locate the ringer circuit?

Wayne Sallee
[email protected]

 

[[email protected]]

Also If I unplug the phone line from the phone for some time, and then
plug it back in, it works.

Wayne Sallee
[email protected]

 

[Ross Herbert]

AOL is really getting discusting. My postings have not been properly
coming through lately. So I had to come to google to read the posts.

But anyway enouph about pathetic aol:

I tryed the REN factor by diconecting other lines to reduce the REN.
But sill it's the phone. When the phone does it speraticaly, it makes
testig more dificult. The speraticness is probably caused by capasitors
charching or discharging, making a slight difference in how the phone
hadles the situation.

Wayne Sallee
[email protected]

You seem to have correctly determined theat the problem is caused by
the phone in question by substitution and other measures so now you
have to determine what is causing the problem inside the phone.

The device which looks like a "light bulb" might be a gas arrestor to
limit lightning surges (by going low resistance) but these devices are
not usual in most telephones. Since you have tried disconnecting this
without any change in symptoms, indicates that this device is not the
problem. You have only mentioned that the phone is by Panasonic and
hinted that it is fairly old but nothing else as to its physical
appearance or construction. The probable manufacturing era might give
us a clue if you can supply this info. From my experience the most
likely cause of the problem is in the ringer circuit as suggested by
Fred McKenzie and Frank Zabkar.

 

[Franc Zabkar]

What's the best way to locate the ringer circuit?

Locate the 1uF or 0.47uF 250VAC capacitor. The ringer is everything
downstream from it.

Wayne Sallee
[email protected]

- Franc Zabkar

 

[Franc Zabkar]

Also If I unplug the phone line from the phone for some time, and then
plug it back in, it works.

Disconnect the phone from the wall socket and measure the voltage at
the socket. Mine measures 52V. Now reconnect the phone. The voltage
should not change significantly, if at all. Take the phone off hook.
The voltage should now drop to around 10V-20V. Hangup the phone and
the voltage should return to 52V or near enough.


- Franc Zabkar

 

[WayneSallee.com]

The device which looks like a "light bulb" might be a gas arrestor to
limit lightning surges (by going low resistance) but these devices are
not usual in most telephones.

I'd say that's probably what it is, as it looks like one of those gass filled
light bulbs.

Wayne Sallee
[email protected]

 

[Dbowey]

wayne posted:

I'd say that's probably what it is, as it looks like one of those gass filled
light bulbs.

Some 60's vintage phone circuits used an NE2 in the ringer. It modulated a
high-piched oscillator to create a "tweet" effect. Also, you could observe the
NE2 flashing through the phone's translucent case.

Don

 

[WayneSallee.com]

Some 60's vintage phone circuits used an NE2 in the ringer. It modulated a
high-piched oscillator to create a "tweet" effect. Also, you could observe
the
NE2 flashing through the phone's translucent case.

Don

This one does not flash, but it might if the voltage was increased enouph

Wayne Sallee
[email protected]