What was the first system to use flash or beep codes as a diagnostic?

Question

It has long been the case that computer systems can signal serious faults using a series of beeps or flashes, where such faults occur too early in the boot process for them to be communicated in more conventional form.

There is a long history of this: modern PCs' motherboards can beep or flash their errors, and going back to 1986 the Sun 3/50 could indicate serious faults with the set of LEDs on its back panel.

What was the first system to use such a method? I'm interested in systems which had some kind of text interface as well; I'm aware that systems with only lights and switches could do little else.

Answer 1

Going back to mainframes which had wide words and large panels of indicator lights, it was possible to display messages on CPU registers quite comfortably. For example, on BESM-6 the boot-up error messages, like "NO BT DSK" or "DISK ERR", but in Russian, of course, were displayed using data cache registers consisting of 8 48-bit words (the second shelf from the bottom of the leftmost rack, with a large whitish rectangle of neon lights in the picture below). An OS even used scrolling to accommodate messages of arbitrary length.

That said, the question effectively asks "What was the first system with too few lights on the front panel to write letters or to scroll dots and dashes?"

Answer 2

The Harwell Dekatron, which is the oldest computer still in working order, has lights on its main control panel to indicate whether it completed its program successfully or halted due to an error. (If it was still running, you would hear the relays clicking and/or the very loud tape reader.)

Its main output was either by punching a paper tape or printing on a modified teletype. I don't think it could print text, only numbers.

An unusual feature of the machine was that you could also read the contents of main memory and the arithmetic accumulator directly by eye, due to the ionisation path maintained by the Dekatron tubes. This must have been a great help for troubleshooting.