Hello,
I have a DFI K6BV3+ with 2 usb ports in motherboard. Both of them supply only 4,2V in power pins, so usb devices don't work.
If i get 5V from other connector (ps2 connector) the usb work and windows recognize the devices, so i think the problem is in some component in power supply line.
How can i check?
Thanks
I'm guessing F2 & L1 are both on the +5V line.
You can measure the resistance of both components when no power is applied. Resistance should be close to zero
or
measure the voltage on both components when a USB device is attached and power is on. Voltage should be close to zero
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https://www.vogonswiki.com/index.php/Serial_port
No power: F2 infinite - L1 close to zero
With power and load: F2 about 4,5V and L1 0V
I checked again pins voltage and voltage going down slowly
normally, when a component is marked F2 I'd assume it's a fuse.
though the markings next to it are a bit insane for USB 5A/125v
From your readings, I'm going for F2 is a defective fuse.
Right to repair is fundamental. You own it, you're allowed to fix it.
How To Ask Questions The Smart Way
Do not ask Why !
https://www.vogonswiki.com/index.php/Serial_port
If F2 it's a fuse, can i bypass the fuse for test?
5A/125V it's very rare values, i think.
Thanks for help
Any thin copper wire will do to bypass that fuse. it should only be rated for about 1.2A 5v (2x USB1.1 500mA/port)
desolder it and see what markings are on the device itself.
Right to repair is fundamental. You own it, you're allowed to fix it.
How To Ask Questions The Smart Way
Do not ask Why !
https://www.vogonswiki.com/index.php/Serial_port
If i bypass the fuse i obtain 5V constant so i think the fuse is defective
Desoldering the fuse i see in bottom "BUSS 5A" and searching in google is very similar to this :
https://www.tedss.com/2026000319
USB work again replacing the fuse by a new one.
Thanks for help.