My old shop's trick for testing laptop power circuits versus just swapping the board

For years, we would just replace the whole motherboard if a laptop wouldn't power on, which is expensive. Last month, I started using a bench power supply set to 19 volts and a current-limited probe to inject power directly at the DC jack solder points. In the last 10 repairs, this method found 7 bad DC jacks or blown fuses, saving the customer over $300 each on a board swap. It takes an extra 15 minutes, but you KNOW exactly where the break is. The bench supply cost me $80 and has already paid for itself. Anyone else have a go-to method for isolating power issues before you commit to a big part?

3 comments

3 Comments

riverhill18d ago

Man, that's a solid method. I always start with a visual check for obvious corrosion or a burnt mosfet by the charging port. Then I'll go in with a multimeter and check for a short to ground on the main power rail. If it's shorted, I'll use some isopropyl alcohol and power it up to see what gets hot. Found a tiny capacitor that way just last week.

alice24217d ago

Honestly, I'd never power up a board with a known short. That's asking to burn a trace or make the problem worse. I always hunt for the short with my meter in resistance mode first, checking each part on that rail. It takes longer but it's way safer. Why risk frying something when you can just trace it out?

troy_fox1d agoMost Upvoted

I used to do the alcohol trick but I killed a good board once by missing a tiny short. Now I always check resistance first like Alice said, it just feels less risky. My meter stays in that mode until I'm sure the rail is clear. The extra five minutes is worth not having to order a new part, lol.