How to use lab power supply

[nazrul145]

Hello boss, how are u? I think everybody is fine. Today i need your help. I think you will be help me how to use lab power supply to find short on laptop motherboard. Pls Share youre knowledge with us and keep update our service line... Thank you.

[khaahk]

Re: How to use lab power supply

If you apply voltage across very low resistance then the result must be many amps.
I apply low voltage (depending on the rail - 1V is mostly enough) and limit the current to 1A and touch by hand, if nothing heats up then it is time to add more amps. If the short is inside a big IC (northbride or smth), then even 3A might turn it only slightly warm. If you give too much amps at once and the short is inside a small cap, then it might burn up and you might get damaged pcb.
The main point is that you don't need to use high voltage to find shorts.
I attach the negative lead with alligator clip to ground and for positive lead i use either a alligator clip with needle or if more amps are needed then soldering is required. I used rather thick wire (~2mm diam) to solder the alligator clips to, because if you don't then the wires are going to heat up instead. If any questions - ask and will try to answer

[nazrul145]

Re: How to use lab power supply

I am not clear about positive lead connection. negative lead connect with pcb ground? and positive lead use with needle. I m not understand what is needle. pls give me an example, how to connect positive lead for finding 3.3v rail short. please clear me. Many many thanks for reply. wait for reply.

[Learn2Day]

Re: How to use lab power supply

Needle is a really thin tip. When using many amps you DON'T want to touch the metal, I use a multimeter tip, it's thin enough and provides you some plastic protection..

One little tip to add, when seeing or feeling heat wasn't working for me, I spread some solder paste around the area, applied current, and the capacitor started bubbling at the bottom almost immediately.

Good luck!