Fixing a Thin Client After 19V Overvoltage

Overview

I made a costly mistake: plugged a 19V power adapter into an HP thin client designed for 12V. The system wouldn’t power on at all. In this video, I reverse-engineer the power input circuit, identify the failed protection diode, remove it, and successfully restore power. This is NOT the proper fix (you should replace the diode), but it demonstrates how a single small component can protect—and disable—an entire computer.

Key Moments

• The mistake: 19V into a 12V-only thin client
• Comparing with a working board to understand the circuit
• Using multimeter in continuity mode to trace the circuit
• Drawing the schematic: capacitor and diode across power input
• Protection diode provides reverse polarity protection
• Finding the short on the broken board
• Lifting one side of the diode with soldering iron and flux
• Testing the fix—system powers on!
• Booting Windows XP successfully
• Creating a label reminder: don’t use wrong adapter again
• Proper fix would be replacing the diode, not removing it

Full Transcript (Edited)

Have you ever wondered what happens when you plug in the wrong power adapter into a delicate piece of technology? Well, I found out the hard way, and now I’m going to take you on a journey to figure out how to fix what I broke.

These are little HP thin clients that I have, and these are my last two of this type. What happened here is that I accidentally plugged in a 19V AC adapter into this working one, and that seems to have blown up something, because these normally run with 12 volts. I just simply plugged it in, and then I quickly realized, “Oh no!” As soon as I plugged in the 12V one—yep, no power, nothing happens.

However, this one, this motherboard came from another one which does power up but it shows no output on the screen. But I’m using the fact that I have this working from a power perspective to see if I can tell what component failed on this side.

[Continues with circuit analysis, diode removal, and successful repair]

The only reason that I’m doing this video is to show that sometimes it’s a small little component that causes the issue, and it’s worth—if you know what you’re doing—to go in there and take a look. However, the right fix here is to replace the defective part. What I did right now is a shortcut, and this is a personal machine. If I plug in the wrong adapter in there again, I will probably damage some other circuitry that is not going to be easy to repair at all.

Lesson is: don’t plug in the wrong adapter. And if you do have to do the fix, do it the right way by getting the correct diode or the correct part and replacing it. If you like this kind of stuff, let me know in the comments below. Hit thumbs up and share it. Alright, till next time, thank you so much!