Very interesting 'scoping results

I happy that you enjoyed that.

Good going. That's just what it's supposed to do. It's a bit dangerous poking round inside line-powered supplies with a scope probe, so if you're going to make a habit of it I'd recommend using an isolation transformer as well.

Cheers

Phil Hobbs

Greetings Phil, I was just checking the low voltage outputs. But now I have the bad supply to check. I have not been able to find a schematic for it after lots of looking and asking so I guess I will be poking around in it. Why the isolation transformer? Thanks, Eric

That's to prevent flames from shooting out of your nether region :-)

So you don't electrocute yourself by some fat-fingered move while poking around inside. I almost did that when I was 14 years old, building a

The power supply went through the window, dropped 2 stories and knocked a couple of shingles off a porch roof before embedding itself in the ground. (Still worked though.) I woke up leaning against the opposite wall. If it had been a 400 volt supply, I might well have died, because the spasm in my triceps might not have been strong enough to break my grip, and of course moderately high voltages like that more commonly cause heart fibrillation, because there isn't enough current to completely reset the heart rhythm.

An isolation transformer won't save you from fat-fingeredness on that scale, but it will usually keep you from frying yourself with the AC mains.

And keep one hand in your pocket.

Cheers

Phil Hobbs

I thought the isolation transformer advice was being given because it protects the oscilloscope. I do keep one hand in a pocket when checking high voltages. After getting a few whopper shocks when I was a kid I learned to respect electricity. Nevertheless, I will get an isolation transformer to use when testing the bad power supply. Eric

The incident that made sure I was careful of high voltage in the future was when I was about 14 too. I don't really remember the shock, I remember banging my elbow against something, which hurt, as my arm jerked away from the high voltage (which was a lower high voltage). It was the hurt elbow that is the reason I'm more careful. Though I can (not so vividly) remember that funny feeling from touching B+ and ground, so different from the funny feeling when I accidentally put my fingers across the 120VAC line.

The important thing is to hope the lesson comes early, because otherwise it's fatal.

Michael

Chance would be a fine thing ;-)

It wouldn't, as I noted in the part you snipped. However, every bit helps.

Cheers

Phil Hobbs