5 Stations
Issue 1, Nov 1973

Self-Contained Keyphone with 10 PPS Signalling

This Instruction gives maintenance information on Telephone 1/SA 4275 which is a self-contained keyphone with 10 pps signalling, based on the Telephone 746. The telephone is at present the subject of trials being held in selected Areas by THQ/TMkD. A description of the instrument and installation details are contained in C3 B3021.

Circuit and wiring diagrams are contained in Dgm SA(L) 4275.

On-site maintenance of this instrument is restricted to the replacing of standard parts as used on the Telephone 746 (see E5 B2676) and the changing of faulty batteries. For all other faults the instrument must be changed. Attempts must not be made to repair or adjust faulty push-button units (pbu). Faulty telephones, with a fault label attached giving details of the fault, should be returned to Supplies Dept in the normal way.

A rechargeable nickel-cadmium 7.2V/150 mAh capacity battery is provided in the telephone to drive the circuits associated with the pbu. it is mounted in a metal clip on the gravity-switch gantry. The battery will discharge if the handset is not replaced and care must be taken to replace the handset correctly at all times. When the telephone is being stored or is in transit a 12 mm wide rubber band should be placed around the base of the telephone and over the plungers in such a way as to keep the plungers depressed.

NOTE: The red battery lead is connected to the red sleeved positive end of the battery.


Battery Charging
The method used to charge the battery is determined by the installation requirements (see C3 B3021) and may be either "on-hook", i.e. battery being charged while the receiver is on its rest, or "on-hook" and off-hook", i.e. battery being charged while the receiver is on its rest and also while the receiver is off rest.

On-hook Charging
Telephone 1/SA 4275 is issued complete with Kit 213A for on-hook charging.

On-hook and Off-hook Charging
Telephone 1/SA 4275 may be converted to on-hook and off-hook charging by fitting Kit 275A in place of the existing Kit 213A and providing a local power supply.

Spare Batteries
Spare batteries (unchanged), coded 6/150 DK, will be supplied by THQ/SvD/Sv5.3.2 to those Areas participating in the trials.

Until a battery charging/dispensing unit is available, arrangements should be made to keep spare batteries on charge using a Power Unit 53A. A maximum of 80 Keyphone batteries in parallel can be charged from one of these 12V power units at one time. It is important that the charging current is restricted to 3 ma and a suitable dropping resistor should be inserted to ensure this value is not exceeded. Ensure correct polarity of battery and power unit as reversal will result in change of battery polarity and subsequent damage to the telephone.

Kit 213A
Telephone 1/SA 4275 is issued with Kit 213A fitted in position on the back of the keypad printed wiring board. Kit 213A consists of an electronic circuit on a printed wiring board. This circuit disconnects the battery when the line is tested. After normal line conditions have been restored for about 30-100 seconds, the battery is reconnected to line and charging resumes.

Kit 275A
Kit 275A consists of an electronic circuit mounted on a printed wiring board. This kit replaces Kit 213A to provide on-hook and off-hook charging from a Power Unit 53A or from a PMBX2/.... switchboard power supply.

Charge Current
Kit 213A Fitted
Disconnect the red wire from the positive terminal of the battery and connect the positive lead of a meter multi-range to this wire. Connect the negative lead of the meter to the battery terminal. With the plungers of the gravity switch depressed, a period of about 30-100 seconds should elapse before a charge of 1-3 ma is observed.

Kit 275A Fitted
Connect a meter multi-range as detailed above with the receiver either on or off-rest, a constant charge of 1-3 ma should be observed.

The pulsing of Telephone 1/SA 4275 is identical to that of a normal telephone dial and should be tested for speed on, all 10 digits, and ratio in the normal manner. The conditions observed when testing towards the telephone will be as follows:-

Telephone Fitted with Kit 213A
Normal line conditions, except that a 15k ohm shunt will appear momentarily across the line at 30-100 second intervals.

Telephone Fitted with Kit 275A
Normal line conditions.

Introduced in 1971 and obsolescent in 1976.  Superseded by the Telephone No. 2/764.

Requires a Power Unit No. 53A.

Introduced in 1972 and obsolescent in 1981.  Superseded by the Telephone No. 756.

Charged via exchange line.

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Last revised: December 17, 2019