why i got shocked !

[watzmann]

Hi All ,

i have a not working power supply board of a network switch ..... i was dignosingthe problem and thought to replace a transistor named k2611 ..... i did that and when i turned the circuit on and touched the heat sink i got shocked but i don't why as this is so strange !!!!!

thanks for your advice

watzmann

 

[KeepItSimpleStupid]

The case of the transistor has a potential attached to it.

In fact, it's the drain: https://pdf1.alldatasheet.com/datasheet-pdf/view/30661/TOSHIBA/2SK2611.html

Insulating washers and thermal grease as well as shoulder washers are used to electrically insulate the case from the heatsink if required.

 

[ChrisP58]

In any mains or line voltage fed power supply. unless you absolutely know that a heatsink is at earth ground potential, it is always best to assume that it is a shock hazard.

Particularly if it was the heatsink for a 900 volt transistor you replaced. If the components have a high voltage rating, then there is a high voltage potential on nearly anything they are connected to.

 

[kubeek]

but i don't why as this is so strange

I think you should not attempt to repair stuff when you don´t know how it works. Especially with mains power supplies you are putting not only yourself but all around you in lethal danger.

 

[dr pepper]

To answer your question directly the reason why you got shocked after you pulled the power is that the smoothing capacitor on the board holds a charge a while after the power is pulled, esp if there is a fault that prevents the supply from pulling any current (but the input stage still works).

If the transistor drain remains at a constant dc potential a while after the power is pulled, then that suggests that either there is no drive to the gate of the transistor ie the controller chip is dead and or the transistor itself is open circuit.

I'm not a killjoy or a lurker but I have to agree with the above post.