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I am fixing an "old" laptop and I needed to replace a broken screen. While disconecting and reconnecting the ribbon cable, I probably shorted something. Now the back light on both the broken and the new screen doesn't turn on.

After some googling and probing I noticed that a P labeled SMD fuse is not conducting. People online usually just short the fuse and call it a day. I would like to be safe and add some protection. The problem is I have no P fuses laying around but I found some K labeled ones in a scrap laptop.

As far as I know the P labeled one is rated for 3A at 32V and the K one is rated for 1.5A at 64V, so the power at which it triggers is about the same.

Can I do the replacement?

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A fuse doesn't trigger on power, but on current flowing through it. So, no, you can't.

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  • \$\begingroup\$ This. Also, I'd add checking if there is a short circuit on either side of the fuse. If you (OP) are lucky, it was a momentary current spike when you plugged the thing in that killed the fuse. If you're unlucky, it blew because of short circuit beyond it (most likely cap, relatively easy fix). If you're very unlucky, you sent backlight voltage into another line and it's probably a goodbye to the device. \$\endgroup\$
    – Ilya
    Commented Apr 23, 2022 at 12:02
  • \$\begingroup\$ Everything except the backlight works plunged in a second monitor and the device is behaving as expected. Also the screen "liquid crystals layers" work fine when I shine at it with an external light, only the backlight pins get no power. \$\endgroup\$
    – jst kiko
    Commented Apr 23, 2022 at 12:11
  • \$\begingroup\$ @jstkiko that doesn't yield any additional information regarding what Ilya mentioned, as the backlight supply is probably used for nothing but backlight. \$\endgroup\$
    – Marcus Müller
    Commented Apr 23, 2022 at 12:14
  • \$\begingroup\$ Even thou you advised me against replacing the fuse I still decided to go through with it. If the laptop dies it dies, it was going to the bin anyway. But luckily it still works, i dont know how long the lower rated fuse will last, but at least I know how to fix it if it dies again. For future readers: this should only be done if you expect the device to die, do this at your own risk. \$\endgroup\$
    – jst kiko
    Commented Apr 23, 2022 at 13:11

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