PSU REPAIR

[Bloudy_Parrot]

so i have an old psu with cut cables which i use for powering my diy projects.

i gave it to a teacher of mine and he wanted to pass curent through a wire in order to heat up wax or something. now the psu isnt even open opening the fan when i connect the green wire to the ground. i want to repair it. what could have gone wrong or failed...the SC protection or....the chip that powers everything on?

 

[mariushm]

Not enough information. 

 

Could be the fuse, could be the controller, could be the transistors / mosfets on the primary side.

 

Sounds like you don't have enough electrical knowledge to mess with the internals of a power supply. So you shouldn't. 

[suedseefrucht]

1 hour ago, Bloudy_Parrot said:

so i have an old psu with cut cables which i use for powering my diy projects.

i gave it to a teacher of mine and he wanted to pass curent through a wire in order to heat up wax or something. now the psu isnt even open opening the fan when i connect the green wire to the ground. i want to repair it. what could have gone wrong or failed...the SC protection or....the chip that powers everything on?

English is not my main language but I try to understand, what you mean...

You have a PSU. Which one?

Your teacher shorted some cables to archieve a high current to melt wax. Which cables?

Now the PSU's fan isn't spinning anymore?

 

There is not only one green wire in the universe of electrical devices...
Is it for the fan's power supply?

 

If an output has been shorted and there is a current limiting or short circuit protection, it should not be dead.
High currents can destroy diodes or FETs.

[Bloudy_Parrot]

2 hours ago, mariushm said:

Sounds like you don't have enough electrical knowledge to mess with the internals of a power supply. So you shouldn't.

To begin with, i dont open the power supply while it is pluged in, i dont have enough time to die this year  also if i do anything wrong and something fails, i have a fire extinguiser just in case. You are right, i am not a professional like you are (i guess), what do i know right? i am just a 14 year old who likes messing with cables. But you know something, i like what i am doing and if i had "enough electrical knowledge" as you say, i wouldn't be asking you right now.

and what does even mean? what kind of knowledge  do i need HUH? soldering...electronic basics.....a master in electronics enegeneering WHAT kind of knowlege do i need to open a power supply.

[seon123]

47 minutes ago, Bloudy_Parrot said:

To begin with, i dont open the power supply while it is pluged in, i dont have enough time to die this year  

If you think it's safe to mess around with the internals of a PSU, just because it's not plugged in, it just proves that

3 hours ago, mariushm said:

you don't have enough electrical knowledge to mess with the internals of a power supply

 

[Bloudy_Parrot]

10 minutes ago, seon123 said:

If you think it's safe to mess around with the internals of a PSU, just because it's not plugged in, it just proves that

 

why tho what could go wrong while it is not plugged in....exept from the charged caps....what else ?

please, tell me

[LWM723]

The charged caps could kill you!

[Bloudy_Parrot]

13 hours ago, LWM723 said:

The charged caps could kill you!

i know, i just discharge them with a resistor

 

[akio123008]

To be very honest though, those charged capacitors are rather low risk anyway. It's all DC.

 

If you want to repair the power supply, and you've failed to diagnose the problem by observing its behavior, the first step would be to open it up for visual inspection.

[Bloudy_Parrot]

ok so, i opened it up as you said and apart from some dust ....everything else looks normal. no burnt components and the fuse is still connected .

[akio123008]

 

On 12/8/2020 at 1:49 PM, mariushm said:

Not enough information. 

This is your main problem. I'd ask that teacher what exactly he's done with it, that could help quite a bit in figuring out what happened.

 

Then there's also the green wire you shorted to GND (power on). You could check the voltage on that wire; it's supposed to be around 5V when it's not shorted.

 

Otherwise you'll just have to probe around with a multimeter until you find the problem. Troubleshooting power supplies is very difficult though, I've torn down plenty of them without success, so be warned.