Fire!

[Dave S]

We had a fairly scary situation the other day in our museum. An RCA 721 was one of several sets running in the display. After this particular set lost picture, we shut it off. But a minute or two later, we noticed that flames were coming out of the cabinet! Although it was a small fire, we had to use a fire extinguisher to put it out, and it was obviously an unsettling situation. We haven't done a full postmortem on the set yet, but according to the initial examination it appears that the filter caps shorted out and caused the power transformer to heat up. Possibly it heated enough to degrade the insulation on the wiring causing a massive increase in current, because the burnt primary leads seem to be the source of the fire. We're not sure yet, but we hope to figure out exactly what happened.

In all my decades monkeying with this stuff, I've never before heard of a case where an electrical fault, even in a 60+ year old piece of equipment, caused a fire. Smoke, sure. We all joke about the magic smoke. But fire?

These sets were made, of course, a long time ago, but I was under the impression that by that point in time things had been designed, especially by big companies like RCA, with safety during failure mode in mind. And I also seem to recall that in order to qualify for the Underwriter's Laboratory seal the equipment had to be designed to fail gracefully, i.e. smoke was acceptable but fire, if any, would be contained.

So I got to wondering, does anyone know how the design of this old equipment dealt with minimizing hazards during inevitable component failure? And has anyone else had the misfortune to actually experience an actual fire in an old piece of electronic equipment?

--Dave Sica

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