Telephone Fault Finding

First things first - if a telephone doesn't work, replace it with a known working telephone to isolate the fault away from the line or socket!

Most faults are very simple.  On the 100, 200 & 300 type range the components generally do not go faulty.

Newly Converted Phone - No dial tone

1. Disconnect the blue and green line cord wires.  Phone should have dial tone, be able to dial out but will get no incoming ring.
2. Double check wiring and metal straps.
3. Remove new installed rectifier 205 if fitted.

No Dial Tone

1. Ensure that dial is in the home position.
2. On 706, 710 and 711 telephones - make sure that there is a small regulator card, that is plugged into the phone,  between the switchooks and that it is inserted properly.
3. Check connections are good on handset cord and line cord.
4. Check that switch hooks are functioning mechanically.
5. On Bakelite and wooden phones ensure that the receiver has a diaphragm (metal plate) fitted under the earcap (slide sideways to remove).
6. Check that the two non-impulse contacts on the rear of the dial are apart when the dial is normal.
7. Listen on the receiver (don't put to close to ear) and with a screwdriver - short out transmitter - if you get dial tone then transmitter is missing or faulty.
8. Listen on the receiver (don't put to close to ear) and with a screwdriver - short out the impulse contacts on the back of the dial (these are normally closed) - you should lose dial tone when shorting one set of contacts.
9. With a screwdriver - short out the switch hook contacts one at a time (there are two on the Bakelite telephones - you cannot do this on a 746 telephone).

Noise whilst talking

1. Listen on the receiver, dial a digit 2 and blow gently into the mouthpiece - if you hear a sound like frying bacon then the microphone is faulty - replace with the same type or upgrade to a modern electronic microphone.
2. On 746 type telephones listen on the receiver and very slowly move the switch hooks up and down.  If you hear a harsh crackling then the switch hooks are faulty.  These cannot be replaced, so it's a new circuit board - try spraying the switch with a general purpose switch cleaner, it may work.
3. Clonking/knocking noise is handset moved on 700 type phones is normally the receiver.  This can only be replaced.
4. General noise which worsens if handset is moved.  Possibly the handset cord - normally goes faulty where the cord meets the handset.  Pull the handset cord tight and test - if the noise goes then you have the culprit.  Remedy is replacement on 700 type phones, or cut back on cloth covered cords.

Bell does not ring

1. If the phone is converted then check that the resistor is installed or a metal link is fitted in place of the resistor.
2. Ensure that bell fixings screws are all present and that bell mechanism is free and that the clapper arm can swing from side to side.
3. Ensure that bell gongs are not touching the bell clapper arm.
4. On 700 type telephones, metal swarf can sometimes be attracted to the magnet and get into the mechanism.
5. Bell ON/OFF switch operated.

Bell faint

1. Bell gong fixing screws are loose and gongs have rotated and closed together.
2. Bell clapper has dropped off - replacement needed of the whole bell assembly.
3. On 700 type telephones - paper wedged between clapper and bell gongs.
4. On 300 types telephones, paper jammed in the paper tray.

Faint outgoing speech

1. Generally the mouthpiece - on Bakelite's check that microphone is seated OK.
2. If the caller is unable to hear completely, but you can hear them, then check the dial contacts.  With the dial normal the two small contacts should be apart.
3. On 200 and 300 telephones bad transmission is generally a faulty old transmitter.

Faint incoming speech

1. Generally a faulty earpiece on 700 type telephones - replace (clue is normally a rattle from the earpiece).
2. On Bakelite's - remove the earpiece cover, then remove the earpiece diaphragm (by sliding the metal plate sideways) and check that there is no swarf on top of the pole faces inside the earpiece and that the plate is clean and not rusty.
3. Also check that the two fixing screws are not loose as these form part of the circuit.

Unable to dial out

1. Check that dial is running at the right speed - dial a digit 0 and as it returns say the following at normal speech speed - "one one thousand and one".  The dial should reach it's stop as you finish.
2. Check that dial is wired up correctly.  On 300 types ensure that the dial is also connected to the terminals block inside the phone correctly as well (looking at rear of dial and the contact set screws upper most the dial is wired from left to right as Blue - Grey - Brown - Pink - Orange.

Dial is slow to return or stiff

1. The dial governor should be checked for dust and fluff.  Oil sparingly the bearings and the governor cup face sparingly (a dab of light oil on the end of a small screwdriver.
2. The dial centre spindle could be seizing.  Normally a strip down - try dropping a very small amount of oil into the central spindle first.
3. The return spring could be broken - requires replacement.
   
   Warning - removing the dial return spring can be dangerous, as it is under tension and is made of spring steel.

Dial does not return

1. Dial return spring broken - requires complete strip down - purchase a replacement and either transplant spring or migrate dial parts to replacement dial.
2. Finger stop bent and fouling on finger plate.

Loud clicking noise in ear whilst dialing out

1. Usual cause is one of the two smaller springs on the dial - clean the contacts.  Test by shorting out the contacts one at a time.  One contact will disable the microphone and the other the receiver.

Last revised: April 08, 2010