Fosi K5 Pro not recognized on PC startup (USB boot loop)

[Streju]

Hi everyone,

I have a Fosi K5 Pro connected via USB to a Gigabyte B650 motherboard. Every time I turn on the PC, I get this issue:

• The Issue: The DAC's blue LED turns on, but Windows doesn't recognize it. Instead of connecting, it gets stuck in a loop, making a rhythmic "pop... pop..." sound in the headphones every 2 seconds.
• The Workaround: If I manually turn the DAC off and on using the physical volume knob, I hear the internal relay click IRL, and it instantly connects to Windows and works flawlessly.
• What I've tried: Moved the cable to a standard USB 2.0 port and disabled "USB Selective Suspend" in Windows. The issue persists.

It looks like a USB power handshake/initialization issue at cold boot. Has anyone experienced this or knows any specific BIOS/Windows tweaks to fix it?

Thanks!

 

[Redacted]

In no particular order...

Try a powered USB extender in case there is a power up problem with USB ports on your mobo with the DAC.

Disconnect any other devices that are using USB as just a boot up test, as sometimes, available current is shared across several usb ports.

Sometimes mobos have a high-current or charging port - if so try that.

Check if there are newer USB drivers for your mobo.

 

[Streju]

Thanks for the suggestions, I just tried everything:

1. Disconnected ALL other USB devices and plugged the DAC into the high-current red USB 3.2 port.
2. Used a high-quality powered USB hub (Hama) connected to my pc.
3. I even updated the AMD B650 chipset drivers to the latest version just in case.

The issue still happens on a cold boot (turning the PC on). The DAC's relay clicks once, but then it immediately falls back into that "pop... pop..." loop.

However if I do a "Restart" from Windows, the DAC connects instantly and works flawlessly. It ONLY fails on a cold boot.

Given this behavior, does this point strictly to a Windows Fast Startup issue or a specific BIOS USB initialization setting? and I can't find "disable fast start up" in power options, I will try and disable that first even tho I think its disabled.

 

[Redacted]

yes - disable fast startup; worth a test. who knows what software state the PC is in when it starts with fast start!
You may also look in power settings for USB and try max of whatever, no suspend etc. Same with PCie settings.
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This kind of stuff:
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[Streju]

So just to recap the current state:

• Fast Startup is 100% disabled (had to re-enable hibernate via cmd just to uncheck it).
• USB Selective Suspend is disabled.
• PCIe Link State is Off.
• ErP is enabled in BIOS (no power to USB when shut down).
• Fast Boot / XHCI Hand-off are set correctly.
• Tested on a red high-current USB port AND a wall-powered external USB hub.

And yet, the cold boot loop still happens. The DAC just goes "pop... pop..." until I manually turn it off and on from its physical volume knob, after which it works flawlessly.

At this point, I'm thinking it's just a bizarre hardware handshake quirk between the Gigabyte B650 chipset and the Fosi controller. Do you happen to know if Fosi ever releases firmware updates for the K5 Pro, or is my only real fix just using the physical knob every day?