Fault Isolation: Device Not Detected

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Fault Isolation: Device Not Detected

A step-by-step fault isolation procedure for a ZDMA that does not appear in Device Manager. Start at TASK 10 and follow the branch that matches what you observe — each task sends you to exactly one next task, so you never have to guess what to try next.

Symptom

The ZDMA does not appear in Device Manager on the Debug PC, or appears with a yellow warning mark, or appears and disappears repeatedly.

Entry point: TASK 10. Do not skip tasks — each one rules out a cause that later tasks assume is already clear.

System description

Two computers are involved. Confirm which is which before you start; most confusion comes from working on the wrong machine.

  • Debug PC — the PC you operate. The ZDMA connects to it over a Thunderbolt cable, and the device must appear in its Device Manager. Every task in this procedure is performed here.
  • Target PC — the PC the ZDMA card is plugged into (the machine being read or tested). Nothing in this procedure is done on it.
Signal pathZDMA card (installed in the Target PC) → Thunderbolt cable → Thunderbolt / USB4 port on the Debug PC. Every port, driver and BIOS setting referenced below is on the Debug PC.

Indicators and connectors

The ZDMA has two Thunderbolt ports and one JTAG port. Each Thunderbolt port has its own green LED; a separate amber LED shows card status. Because of compatibility, usually only one of the two Thunderbolt ports is effective.

  • Amber solid — card powered and running. Not tied to a port.
  • Port green solid — that port is the effective one; link established.
  • Port green off or blinking — that port is not effective.
Normal indicationAmber LED solid and the green LED beside the port in use solid. Any other indication — off or blinking — is abnormal.
JTAG portJTAG runs at USB 2.0 only. A high-specification cable, including the bundled Thunderbolt cable, is often not compatible with it. Use an ordinary, low-cost USB cable for JTAG.

Fault isolation flow

Task What it rules out Exit
TASK 10 Firmware corrupted or wrongly flashed Pass → TASK 20
TASK 20 Debug PC port is not true Thunderbolt / USB4 Pass → TASK 30
TASK 30 Physical link — port selection, cable, power Pass → TASK 40 · Fail → TASK 50
TASK 40 Windows enumeration — isolates the driver Isolated → CA-A · Fail → TASK 50
TASK 50 BIOS Thunderbolt configuration Pass → end · Fail → TASK 60
TASK 60 Event log classification — link / power / firmware → Report to support

Fault isolation tasks

TASK 10Firmware status

Clear this first. A wrong or failed flash produces exactly the same symptom as a cable or driver fault, and no amount of driver work will correct it.

Has FPGA firmware ever been flashed on this card?

YesRestore the factory / default firmware, then retest. See the ZDMA Firmware Flashing Guide. Still not detected after restoring? → TASK 20
NoFirmware is not a factor. → TASK 20
Standing ruleTest a new ZDMA before flashing anything. Update firmware only after the card has tested good.
TASK 20Debug PC port identification

The ZDMA can only be reached through a genuine Thunderbolt or USB4 port. A plain USB-C port is physically identical but will never carry the device.

Is the Debug PC port a true Thunderbolt / USB4 port?

  1. Look for a small lightning-bolt icon printed beside the USB-C port. No bolt usually means no Thunderbolt.
  2. If unsure, identify the machine using the AI diagnostic aid below — it reads your actual hardware and answers this for you.
YesPort type confirmed. → TASK 30
NoIsolated Wrong port type. Move to a true Thunderbolt / USB4 port on the Debug PC. If the machine has none it cannot serve as the Debug PC — a USB 3.x-only Type-C port will never work. End of procedure.
TASK 30Physical link — indicator check

Establish the physical link before considering Windows at all.

With the cable connected, is the amber LED solid and the green LED beside the port in use solid?

YesPhysical link established. → TASK 40
NoWork through 30A, then 30B below.

30A — Port selection. Move the Thunderbolt cable to the ZDMA’s other Thunderbolt port and observe the LEDs again. Only one of the two is usually effective.

Green now solidUse this port from now on. → TASK 40
Still not solidContinue to 30B.

30B — Cable and power. Perform all three, retesting after each:

  1. Fit a certified 40 Gbps Thunderbolt 4 cable.
  2. Boot the Debug PC first, then connect the cable — connecting before POST can prevent initialisation.
  3. If the Debug PC is a laptop, set High Performance power mode and connect wall power.
Green now solidPhysical link established. → TASK 40
Still not solidThe link is not coming up. → TASK 50
TASK 40Windows enumeration — re-plug test

This single test separates a driver fault from a link fault.

  1. Open Device Manager on the Debug PC and keep it visible.
  2. Unplug the Thunderbolt cable, wait a moment, then plug it back in.
  3. Watch the list closely at the moment you re-plug.

Does the Device Manager list refresh by itself when you re-plug?

YesIsolated The link is alive and Windows is reacting — this is a Thunderbolt driver fault. → CA-A
NoNo enumeration at all. → TASK 50
TASK 50BIOS configuration

Is Thunderbolt enabled and unrestricted in the Debug PC BIOS?

  1. Enter BIOS/UEFI. Set Thunderbolt Support (or USB4) to Enabled.
  2. Set Security Level to No Security. “User Authorization” silently blocks the card when Control Center is not installed.
  3. Save and exit, reboot, then reconnect and retest.
Now detectedIsolated BIOS configuration. End of procedure.
Still not detected→ TASK 60
NoteOn many AMD USB4 boards this setting is buried or named differently. The AI diagnostic aid below will give the exact menu path for your board.
TASK 60Event log classification

Classify the failure before reporting it.

  1. Open Event Viewer → Windows Logs → System.
  2. Filter by source Kernel-PnP and WHEA-Logger.
  3. Record the most recent entries from the time of the fault.

These entries indicate whether the failure is link, power or firmware related. Include them when you report the fault, or paste them into the AI aid below for interpretation. → Report to support

Corrective actions

CA-A

Reinstall the Thunderbolt driver

  1. Obtain the Thunderbolt / USB4 driver and Control Center for your exact motherboard or laptop model, from the manufacturer support page.
  2. Install on the Debug PC — not the Target PC.
  3. Reboot, then reconnect the Thunderbolt cable and retest.

If the device is now detected, the fault is cleared. If it is still not detected after a clean reinstall, → TASK 50.

AI diagnostic aid

Several tasks above need facts about your specific motherboard — whether it truly has Thunderbolt, where the BIOS setting lives, which driver package applies. You do not need to know your model: let an AI read the machine and answer from your real hardware.

Method 1 — System report, sent to any AI

Press Win, type PowerShell, open it, paste the block below and press Enter. A Notepad file opens on your desktop — that is your report. It only reads information and changes nothing.

$o = "$env:USERPROFILE\Desktop\zdma-report.txt"
"=== System ===" | Out-File $o
Get-CimInstance Win32_ComputerSystem | Select Manufacturer,Model | Out-File $o -Append
Get-CimInstance Win32_BaseBoard | Select Manufacturer,Product | Out-File $o -Append
(Get-CimInstance Win32_OperatingSystem).Caption | Out-File $o -Append
"`n=== Thunderbolt / USB4 controllers ===" | Out-File $o -Append
Get-PnpDevice | ? { $_.FriendlyName -match 'Thunderbolt|USB4|JHL|Ridge' } | Select Status,Class,FriendlyName | Format-Table -Auto | Out-File $o -Append
"`n=== Devices with a problem ===" | Out-File $o -Append
Get-PnpDevice | ? { $_.Present -and $_.Status -ne 'OK' } | Select Status,Class,FriendlyName | Format-Table -Auto | Out-File $o -Append
"`n=== Recent PnP / WHEA errors ===" | Out-File $o -Append
Get-WinEvent -FilterHashtable @{ LogName='System'; ProviderName='Microsoft-Windows-Kernel-PnP','Microsoft-Windows-WHEA-Logger' } -MaxEvents 15 -EA SilentlyContinue | Select TimeCreated,Id,Message | Format-List | Out-File $o -Append
notepad $o

Copy the whole report and send it with this prompt:

I have a ZDMA card (a Thunderbolt/USB4 DMA device) plugged into my Target PC, connected by a Thunderbolt cable to my Debug PC (the computer I operate), and the Debug PC's Windows won't detect the device. Below is a system report from that Debug PC. Based on it, tell me in plain language:
1. Does this machine actually have real Thunderbolt/USB4, and which port should I use?
2. The exact BIOS steps for THIS motherboard to enable Thunderbolt Support and set Security Level to No Security.
3. The exact Thunderbolt/USB4 driver + Control Center download for THIS model, and the install order.
4. What the Kernel-PnP / WHEA errors in the report mean - link, power, or firmware?
Ask me only for what's missing.

--- SYSTEM REPORT ---
[paste the whole report here]

Method 2 — An AI that reads the PC itself

These tools run commands on your PC, so you paste nothing — the AI collects the hardware information itself.

Chinese

Doubao

Free desktop assistant that can inspect your PC. Easiest choice if you prefer Chinese.


Technical

Claude Code

Runs in a terminal, reads your system and works through fixes with you.


Technical

OpenAI Codex

An agent CLI that can run commands and troubleshoot on your machine.

You can run PowerShell commands on my Windows PC. This PC is my Debug PC - the one I operate. A ZDMA card (a Thunderbolt/USB4 DMA device) is plugged into a separate Target PC and connected to this Debug PC by a Thunderbolt cable, but this Debug PC's Windows won't detect the device (it doesn't show in Device Manager, though the device's green light is on).

Don't ask me for hardware details - find them yourself. Run commands to collect: motherboard and system model, Windows version, any Thunderbolt/USB4 controllers and their driver status, any present devices whose status isn't OK, and recent Kernel-PnP and WHEA-Logger errors from the System event log.

Then tell me, in plain language:
1. Whether this machine has real Thunderbolt/USB4 and which port to use.
2. The exact BIOS steps for this motherboard to enable Thunderbolt Support and set Security Level to No Security.
3. The exact driver + Thunderbolt Control Center download for this model, and the install order.
Explain each step simply and wait for my confirmation before making any change.
Why this is more reliableThe AI reads your actual system rather than a model number recalled from memory, so it cannot misidentify your hardware — which is precisely the part that normally requires an experienced PC technician.

Fault not isolated — reporting

If you have completed TASK 10 through TASK 60 and the device is still not detected, report the fault with the following. Supplying all of it lets us answer on the first reply instead of asking back and forth.

  • Last task reached, and the branch you took at each decision.
  • Motherboard or laptop model, exact — for example ASUS ProArt X870E.
  • Device Manager screenshot with the cable connected.
  • BIOS screenshot of the Thunderbolt / Security Level setting.
  • LED indication — amber and green, solid / blinking / off, and which port was used.
  • Device SID, printed on the label.
  • Firmware history — flashed, or still factory?
  • Event log entries recorded in TASK 60.

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