This repair service/tutorial video clip by the phone Connections Museum of Seattle features an wonderful piece of electro-mechanical technology from the 1950s — the 5XB trouble recorder. Museum volunteer Sarah the “Switch Witch” has a deep enthusiasm for aged phone machines, and provides an fantastic description of the hassle recorder, the difficulties it solved, and how it operates, and how they went about repairing it.
As central workplace switching became additional intricate and extra dense, the manual strategies of searching down faults turned unmanageable. Semi-automated strategies making use of trouble lamps, but even that experienced its limits. This “stack trace”, which could have hundreds of indicators, had to be frozen although the technician recorded the position on a form. If one more fault came alongside for the duration of this time, it was dropped. The remedy, working with the out there technology of the day, was a mind-boggling punched card apparatus that punches more than a thousand bits of data when an switching error is detected or when different watchdog timers expire.
The difficulties recorder in the Connections Museum was not really operating. But with a ton of tolerance and accessibility to a assistance guide, the staff eventually received it up and working yet again. Now the greatest issue now is acquiring new blank cards printed when the several packing containers they have finally run out.
If you are intrigued in these sorts of intricate electro-mechanical methods, do look at out the video under. We in particular liked the system that broke up 1200 bits into a timed sequence of 10 every 120 bits to generate the punches employing motors, cams, gears and relay contacts. You can read through extra about this difficulty recorder in this Bell Labs Report technological report (pg 214) from Could 1950 (curiously, this concern sales opportunities off with Dr Hamming’s famous paper on error detection and correction codes).