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'Sup's that go "Boom"

posted Dec 6, 2020, 7:28 PM by Charles Boling   [ updated Dec 25, 2020, 12:34 PM ]
We like the 'sup's -
The 'sup's that go "Boom".
We're Alex & Chucky
And We like the boom.

(with a nod to the '80s' hit, "Cars That Go Boom" by L'Trimm)

KD7TJR's power supply didn't fare as well. It had previously blown a fuse and damaged a resistor. As it turns out, one of a pair of power transistors failed. Alexander removed the resistor and, after some time examining the schematic, determined that it was likely that doing so would remove the voltage applied to the base and likely reduce the load that the transistor was sinking. I was trying to get "real" work done and not paying too much attention myself, but we decided to power it up briefly and measure the current draw.

Looks like it was the wrong approach; apparently the base was biased from somewhere else and removing the resistor (which would've happened by itself had we powered it up a 2nd time with it still in there, judging from the damage done by the previous run) opened the emitter-collector gate wide, and the resulting current rush violently melted the collector pin.

The good news is that, as you can see, I did catch some good pictures of its final act (which blew a couple more components as well) in spite of the fact that the stupid camera was set for 120fps, but for some reason it merely duplicated each frame 4x, making it effectively 30fps.

If you look carefully at the first picture (click the pictures to see full-size copies), you can see a single streak coming from the collector. It progresses from there. My mini tripod disappeared, so I was holding the camera in my hand, and my involuntary jerk is obvious.  It was a loud crack and a bright flash!

It was interesting watching & listening to the video slowed down 32x (1fps); in the frame before the first one shown, you can hear the initial small "boom" that of that first spark, then you can hear multiple explosions as the fireball builds; it sounds like a barrage of cannon fire. Neato! Sad, though; we decided that it's not worth the effort of buying & replacing multiple parts when we don't even know for sure that the transistor was the root cause, so we're laying the whole thing to rest.
Charles Boling,
Dec 25, 2020, 12:32 PM
Charles Boling,
Dec 25, 2020, 12:27 PM