Cool Video about 70's Electronics

[Zak]

I was recommended this German YouTube video about electronics from 1974.

The title says "introduction into digital technology. Part 1: the principle of small steps (1974)". I hope you can understand the translation of the automatic subtitles, which are a bit imprecise. Once you clicked the subtitles symbol, you can click the otions symbol and then click on subtitles, then select automatic translation (if you didn't know that already ).

[ Show youtube player ]

[Bruce Abbott]

The rotary dial telephone and relays bring back memories.

I was trained as a telephone exchange technician starting in 1976, working on equipment that was designed in the 1930s. Everything was done with relays and electromechanical rotary switches. The exchange I worked in (in Hastings, New Zealand) had 20,000 phone lines, and at peak traffic times the noise of all those relays and switches operating was deafening. It was powered by 50V DC and drew up to 600 amps. The bus bars that carried the current from the battery room up to the switchroom were as thick as my arm.

In the 1980's it was upgraded to a solid-state NEC NEAX 'stored program control' system that converted the analogue speech signals to PCM and was controlled by two proprietary central processing units running in parallel for redundancy. This system drew ~500 amps continuously even when idle - more current on average than the electromechanical system! It was much quieter though.

By this time I was working on outlying exchanges and didn't get any training on the NEAX, however I occasionally had to interact with it when working on trunk lines (connections from one exchange to another). The interesting part is that this sometimes involved programming 'patches' into the NEAX that were written in asm code. That was the job of the NEAX technicians, but I remember one time the patch didn't work and I was able to tell the technician what was wrong with it even though I had never seen the asm code for this system before.

I also worked on PBX (Private Branch Exchange) systems in local businesses. These went solid-state around the same time, but were much smaller systems typically controlled by an 8 bit microprocessor such as an 8085 or 6809. Servicing these was supposed to be restricted to replacing modules, and we got no training on the internal system software or hardware.

Of course these early PBX systems were full of bugs which we couldn't do anything about except report them, and manufacturers were very tardy at providing fixes. In one system the operator's console had a 'feature' that the incoming call buzzer wouldn't sound if she was already on a call, which meant calls would be missed and customers got upset. The manufacturer refused to modify it so I hacked into the ROM and patched it. The only documentation I had at the time was a one page summary of the 8031 instruction set.

Good times!