BT Cardphone 1A

BT Card Phone 1A
CARDPHONE 1A SGZ/81 Mark Number/1

Ive Just got this phone into my collection, I'll post here as I found out more about it.

This white model was on tomorrows world ..

tomorrows world

Birds of a Feather prison card phone

Payphone card phone birds of a feather


Ive powered up my phone from a 24v AC supply and a Testel 200 payphone line simulator.

On picking up the phone, I get a dial tone and "000" flashes on the display.

Inserting a card causes it to be ejected immediately.

Inserting a card upside down causes the reader to move the read head for a second then the card is ejected again.

The phone continues to flash "000"

Thanks to for the green Fault codes from a more modern card phone

Pressing the test button on the phones logic card causes the display..











1 18

2 8

3 1

4 15

then blank with tones to line and in earpiece

Inserting a card causes it to be ejected immediately. The tones mute for a while the display will then show


Inserting a card upside down causes the reader to move the read head for a second then the card is ejected again.

10 is shown on the display

putting the card in sideways causes

03 if the card jams on the carriage

removing the fuse from the card reader pcb, then running the tests again causes the code

"61" -

Fault codes from a later BT Phonecard phone
61 - reader not switched on

after the 1111-9999 count

pressing test again gives

1 18

2 8

3 1

4 15

replacing the fuse causes the "23" and "10" results from card inserts as before

If I manually wind the carriage to the other end, when the card is inserted the carriage returns before exhibiting the same

"23" and "10" results from card inserts.

The interface between the reader and the phone

There are 3 Opto isolators in the reader which seem closely connected to the ribbon cable to the phone.

I could guess 1 is data out 1 data in and perhaps 1 for reset ?

BT Phonecard 1A - Opto isolators in SK30 Land & Gry reader

Both the phone and card reader have a RCA CDP1854CD UART so I would guess the comms between the card reader and phone is some sort of current loop asynchronous serial. says

The interface between the reader and the telephone incorporates the following functions

  1. Recognise valid cards - by verification of the family code

  2. decode the information bits of the type code

  3. command the read and erase processes

  4. command the carriage movement

  5. count the number of value bits erased and by subtraction deduce the balance remaining on the card

The input signals to the reader are

  1. Read command

  2. Erase command

  3. Carriage advance command

  4. Eject card command

The card reader outputs the following information

  1. Card present

  2. Beginning of track

  3. Presence of valid value bit

There must also be error states output from the card reader.

Landis & Gyr Optical Test Cards for BT

Ive looked on the internet for all the testcards i can find and plotted V0 and V1 against the numbers that follow..

They look like straight lines to me.

Landis & Gyr Test cards
Graph of BT phone card detector voltage against number


In November 1988 the "Summary of Charges for Telecommunications Services PH3824" on Page 42 says.

£74 connection, £101.50 Quarterly rental, £115 for new line,£26.75 Quarterly business line rental +£17.00 connection and £2.50 per Quarter for meter pulse.

Eprom Images

The SK30 Card reader has 2 MBM2716 Eproms on a PCB Marked SK.30 carte E

IC 12 is marked Chip 1 and IC 11 is marked Chip 2

The Phone it self has a PCB marked TK12 Carte Logique, this has 4 eprom sockets, none of which have eproms in them, instead IC 12 has a DIL plug and a ribbon cable leading to a eprom daughter card with 12 x 24 pin dil sockets.

In the first 7 of these are intercil im6654IJG eproms, the other sockets are empty. The Intercil IM6654 is an 8 by 512 cmos eprom. So the total software on the card is 3.5k bytes.

Intercil .5 k eprom