Connect with us

Telephone Disconects on First Ring

Discussion in 'Electronic Repair' started by WayneSallee.com, Jan 5, 2005.

Scroll to continue with content
  1. 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
     
  2. And it is the phone, not the phone line shorting out.

    I've already fully tested that.

    Wayne Sallee
     
  3. Guest

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

    Richard
     
  4. << 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
     
  5. Dbowey

    Dbowey Guest

    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
     
  6. w_tom

    w_tom Guest

    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.
     
  7. Guest

    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.
     
  8. 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


    In a message dated 1/5/2005 1:19:16 PM Eastern Standard Time,
    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
     
  9. Franc Zabkar

    Franc Zabkar Guest

    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
     
  10. Franc Zabkar

    Franc Zabkar Guest

    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
     
  11. Guest

    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
     
  12. Guest

    I've already done all that.

    Wayne Sallee
     
  13. Guest

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

    Wayne Sallee
     
  14. Guest

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

    Wayne Sallee
     
  15. Ross Herbert

    Ross Herbert Guest

    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.
     
  16. Franc Zabkar

    Franc Zabkar Guest

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

    - Franc Zabkar
     
  17. Franc Zabkar

    Franc Zabkar Guest

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

    Wayne Sallee
     
  19. Dbowey

    Dbowey Guest

    wayne posted:
    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
     
  20. This one does not flash, but it might if the voltage was increased enouph :)

    Wayne Sallee
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-