EEVblog #363 - Gold Phone Teardown

[Cranky]

Wow. This brought back some memories.
I serviced these for about 14 years.

A bit of info...
These phones were operated by customers leasing them from Telecom (at that time) CT4 = customer telephone 4.

They were obviously line powered (48V positive earth) as you have discovered and the super caps on the bottom of the mainboard would run the electronics during a call.

They were also polarity sensitive. They would power up and accept coins when connected in either polarity but would drop the call on answer if the polarity was incorrect.
Speaking of which, in normal operation the phone would accept coins into the mech' whenever the display was active. I am guessing the coin mech' in the video was faulty as it should have accepted coins when they were inserted.

It would collect coins into the cash box on answer, and then collect the set amount every time it would receive a meter pulse (for multi-metered aka long distance calls).
On answer the line polarity reversed, then within 250mS it should receive a 50Hz longitudinal meter pulse of 250mS duration. The meter pulse was the same amplitude and phase on both 'legs' of the line and was referenced to earth. (The goldphone required an earth to operate.)
The lift up mechanism allowed the service tech to test the coin mechanism by making a test call to designated test numbers and the coins collected would drop into the refund chute, not into the cash box. (Calls to these numbers weren't charged to the lessee of the phone.)

The coin mech' would use the coils to measure the thickness, diameter and material of the coin to determine its value.
The little kicker solenoid wouldn't pull in acceptance of a coin, just depower enough so that the weight of the coin would operate the kicker arm and allow the coin to run into the coin holding area.
Just a bit of trivia: The same coin mech' was used in the green and grey coin and card payphone used in the street at the time.

The tariff unit at the top of the mainboard was able to be modded to adjust the tariff. The left side for the tariff on answer and the right side for each subsequent collection.
The three diode positions on each side would set the tariff. from the top down they were 10c, 20c, and 40c, so you could set the tariff from 10c t0 70c just by adding or removing diodes.
The board in the video is set for 50c.
Later revisions of the board had DIP switches to set the tariff.

I still have the maintenance key for the rear lock and quite a few spares parts laying around. I also have 2 complete gold phones as well.

Don