What did I do wrong.

[EddieM]

I've put this is UK electrics although I guess it could easily go into tools or indeed DIY disasters.

Right, firstly I admit my knowledge of electrics is limited to say the least, and my knowledge of electronics even more so.

The problem was the laser on my mitre saw packed up. I took the laser off and ascertained that there was no voltage being registered at the laser. I then took the switch assembly off, and ascertianed there was no voltage output here either. I checked the inpput to the switch assembly, this read 240v. So naturally I reckoned the fault was in the switch assembly which incidentally transforms the 240v AC to 3.3v DC.

I then connected the 240v supply to the switch, and went to test the input to the switch and the output, to see if it was the actual switch itself rather than the transformer gubbins.

When I put the probes on the switch output, there was an electric flash, and I have now truly blown some of the electronics in the switch unit.

Why did this happen, was it because I accidentally connected 2 resistors in parallel ?

Feel free to laugh now.

 

[flameport]

When I put the probes on the switch output

Probes from what? A multimeter? Wrongly set to the Amps/current range?

 

[securespark]

If the switch is SP, then putting a multimeter set up for voltage across the switch will create a few sparks, as you would have been attempting to measure current flow...

I won't laugh. I've done it too....

 

[EddieM]

Nah, it's a DP switch or at least was a DP switch, I don't think the MM was on the wrong range, but why did it toast the electronics?

BTW, it tripped the MCB as well

 

[ban-all-sheds]

If the switch is SP, then putting a multimeter set up for voltage across the switch will create a few sparks, as you would have been attempting to measure current flow....

A multimeter set to voltage has an very high resistance - putting it in series with a circuit won't cause much current to flow at all.

With the switch closed it'd read 0V, with it open it'd read whatever the switch was switching, pretty much, and wouldn't let enough current through to work the <thing> being supplied.

 

[electronicsuk]

Either you accidentally touched across two terminals with one probe without realising it, or you had to meter set up to measure current and managed to put it across 230v. I can't imagine many other possibilities that would result in enough current flowing to trip the breaker.

 

[EddieM]

Hmm, I'm pretty sure I didn't touch the probes together. as obviously this would have been a dead short. I guess I must of had the MM on the wrong range.

Academic I suppose, as I've now well and truly fried it. Oh well it didn't work anyway, another ill afforded £50 notes out of the window.

 

[ban-all-sheds]

Nah, it's a DP switch or at least was a DP switch, I don't think the MM was on the wrong range, but why did it toast the electronics?

BTW, it tripped the MCB as well

I'd say that you had the MM set to a current or resistance range, and when you connected it across the two O/P terminals of the switch (presumably to see what voltage would appear) you effectively shorted the outputs together, and it's not at all unreasonable for the gubbins inside the switch to take a very dim view of a virtual dead short instead of a proper load.

How's the MM?

I can't imagine many other possibilities that would result in enough current flowing to trip the breaker.

I can.

The short across the switch O/P toasted the PSU inside the switch.

That toasting resulted in the PSU becoming a low-impedance fault path, and that's what tripped the MCB, and that's why there were sparks.

 

[electronicsuk]

I can't imagine many other possibilities that would result in enough current flowing to trip the breaker.

I can.

The short across the switch O/P toasted the PSU inside the switch.

That toasting resulted in the PSU becoming a low-impedance fault path, and that's what tripped the MCB, and that's why there were sparks.

Would that be a short caused by...

Either you accidentally touched across two terminals with one probe without realising it, or you had to meter set up to measure current and managed to put it across 230v.

...? I made no reference as to whether the short circuit was made before or after the switch, just suggestions as to how it may have happened.

 

[EddieM]

The Meter seems ok, it wasn't a particularly violent spark or pop, just a flash, a dull fut, and a blackened resistor / transistor / hard to tell what component actually got fried.

 

[ban-all-sheds]

The Meter seems ok, it wasn't a particularly violent spark or pop, just a flash, a dull fut, and a blackened resistor / transistor / hard to tell what component actually got fried.

Try replacing that component - worst case you'll have wasted a lot less than the £50 you'd waste if the thing is repairable.

 

[electronicsuk]

Assuming it's not so black that you can't tell what it was or a value/part number

 

[ban-all-sheds]

There is that...

 

[EddieM]

well, it didn't work before I completely blew it up, I was trying to narrow down whether the laser or the switch had failed. It was the switch, but it's definitely toast now.

Sad thing is I have to buy a new laser along with a new switch, typical!

I guess I'll replace the switch and the laser, and try to flog the old laser on flea bay to recoop some of the exorbitant cost of the new kit.

 

[ban-all-sheds]

Would that be a short caused by...

Either you accidentally touched across two terminals with one probe without realising it, or you had to meter set up to measure current and managed to put it across 230v.

No - not if I understood you correctly.

It looked like you were suggesting that the meter was the short that the supply saw, and what caused the MCB to trip.

I was suggesting that the meter was the short that the PSU saw, and what caused the PSU to toast itself. and it was the toasted PSU that became the short that the supply saw, and what caused the MCB to trip.

If the MM on a current or voltage range was what directly tripped the MCB then it would definitely not be OK now.

Apologies if I did misunderstand.