LED flashes when soldering

Could be plain old ESD discharge. What shoes were you wearing? Is there carpet or non-treated linoleum flooring? Sometimes moving a bit in an office chair with some artificial fiber content in the padding suffices.

I was thinking it may be that. I was wearing 100% cotton and sitting on a wooden stool, but I'm not sure I was remembering my static strap.

Has the soldering iron ground wire lifted?

piglet

I'd bet ESD, but has anyone been able to shuffle on the rug and light an led? I found nothing in Google jb

I don't think there is enough thermocouple voltage to light an led.

Maybe some cap on the board had a charge on it? or ESD as per Joerg.

I did do some ESD testing of a laser diode (while monitoring the light output.) And I'd get a big light spike sometimes when I zapped it.. (that wasn't very good for the diode.)

George H.

Was it a brief flash, or sustained?

Might the soldering iron have some 60 Hz (or if Metcal, RF) current leaking out? 1 uA is visible with a modern LED.

Any battery backups or other power sources?

Could it be that bypass caps were charged? Electrolytics can generate their own voltages!

Hopefully no loose neutral situation in the house ...

Check the ground on your soldering iron. it may have failed, letting some leakage from the heating element through to the tip.

Jon

You're lucky that it flashed. That means you had the non-destructive polarity on your ESD. Some chemistries of LEDs will slowly burn themselves away during use after they get the slightest reverse current. (Those blister packs of 14000 mcd green LEDs at Frys come pre-damaged) It's why you'll see a little blob of MOV next to expensive emitters.

On an unpowered PCB with scope probes still attached, you can see 50Hz mains coupled thorugh the Y capacitors of the solering iron if not ground properly

Cheers

Klaus

Yeah, a 100 A/1 ns spike will reliably put your diode laser way, way above threshold, and the resulting huge light pulse will blow the output facet right off the die.

Cheers

Phil Hobbs

That's interesting. Do you have a link for that?

Thanks

Phil Hobbs

My first clandestine soldering iron that I secretly bought as a kid had no protective earth connection. You could see the glowing coil through little holes at the top of the metal shaft, connected directly to 230VAC mains. The mains plugs in Germany are not keyed so you never know which one is phase.

It is a miracle that I never killed components (maybe I did?) or electrocuted myself with that. All it would have taken is an innocent silver wire lead sticking up and poking through one of those holes.

We're using some Avago optoisolators and I was curious about the LED reverse characteristics. They zener at -45 volts, and a little reverse current doesn't seem to bother them. ACPL227.

My old S38 shortwave receiver had one side of the AC line soldered directly to the chassis, and an unpolarized cord. The chassis was separated from the metal box by 4 rubber grommets, long since disintegrated when I got it. I'd just plug it in the way that didn't light a handheld neon bulb.

Guy I knew was standing waist-deep in Lake Pontchartrain [1] drilling a hole in the side of his sailboat with an old metal-case electric drill. He didn't make it. Those were the days.

When I built my first kilowatt amp for shortwave ham operation I was still a teenager, had just gotten the highest license class but short on money. So a fat transformer wasn't in the cards. But ... we had 230VAC so a 3x Cockroft-Walton and a massive bank of electrolytics made over

Like this guy?

As long as you don't step on anything nasty.

Virtually all the 5-tube AC/DC radios made from 1948 to 1963 had one side of the line connected directly to the chassis. See the switch on the volume control on the right side in the schematic below

I used to tell if the line plug was in the right way by brushing my knuckle against the chassis. If the chassis was hot, you would feel a vibration.

This technique still works today when there is an unexpected AC voltage on a chassis or piece of metal when you brush up against it. It is an instinctive warning that the metal is hot.

That is sometimes true for parts of New Orleans too.

I had one of the "All American Five" radios (Zenith, IIRC) when I was a kid. I remember losing one of the knobs once. I found that a pair of pliers wasn't the right tool to adjust the volume.