Hello,

I have 5 volts supplied by a phone charger. Some green and red LEDs some 2n222 transistors and a 555 timer. While powered up a slip with the meter probe and everything has stopped working. One LED might light up. What is likely to fry instantaneously, any ideas thanks

 

everything has stopped working.

Including the phone charger?

 

Charger still works and one led

 

Which single part would cause all the failures if removed from the circuit? That is what I would check first. Of course it might also be multiple parts.

 

Charger still works and one led

Without a schematic we have no way of knowing what else might be got working again.

 

Also; what exactly did you short?
Do you know how to troubleshoot transistors with a DMM?

 

Hello,

I have 5 volts supplied by a phone charger. Some green and red LEDs some 2n222 transistors and a 555 timer. While powered up a slip with the meter probe and everything has stopped working. One LED might light up. What is likely to fry instantaneously, any ideas, thanks. Also the dmm was set to check current.

Hello guys thanks for all the input. I was looking for what might be likely to fry instantaneously by a misplaced dmm probe. I have wired 555 timers so poorly they got so hot you could fry eggs on them and they would still work. I've put transistors in backwards and they still work. I'm about to go component by component I was just wondering if something is a notorious weak link. Thanks again

 

I have wired 555 timers so poorly they got so hot you could fry eggs on them and they would still work.

If you leave them in that condition long enough, junctions will start melting.

I've put transistors in backwards and they still work.

Are you sure they still work? If you breakdown the base-emitter junction, current gain can be damaged.

I'm about to go component by component I was just wondering if something is a notorious weak link.

Just troubleshoot the problem instead of guessing.

If you ask for help, you should post a schematic so we know what you're dealing with. If you don't know what you're doing, add voltage measurements for important nodes.

 

Here is an analysis based on a guess that the transistor controlled the LEDs that no longer light, and that the probe short circuited some device..
1.) if the probe connected the two leads of an LED to each other, and the transistor had been passing some current to light the LED, then the guess is that the transistor suddenly had five volts, emitter to collector, while switched on. So it would quickly overheat and fail. Or the slip applied 5 volts between the base and emitter, and fried that junction. If that also caused a collector to emitter short inside, then the 5 volts across the LEDs could fail them in a very short time.
If the connection was on the 555 pins, and the +5 applied to the output pin while it was active, the output transistor in the 555 may be failed.
Consider that those guesses are based on no hint as to where the probe was whan it slipped, and no circuit information.

 

Here is an analysis based on a guess that the transistor controlled the LEDs that no longer light, and that the probe short circuited some device..
1.) if the probe connected the two leads of an LED to each other, and the transistor had been passing some current to light the LED, then the guess is that the transistor suddenly had five volts, emitter to collector, while switched on. So it would quickly overheat and fail. Or the slip applied 5 volts between the base and emitter, and fried that junction. If that also caused a collector to emitter short inside, then the 5 volts across the LEDs could fail them in a very short time.
If the connection was on the 555 pins, and the +5 applied to the output pin while it was active, the output transistor in the 555 may be failed.
Consider that those guesses are based on no hint as to where the probe was whan it slipped, and no circuit information.

Thank you, it was a transistor!