HDC403-P23 UBC-C | DP | HDMI - Back USB ports not working
Hi TESmart,
2 weeks ago, I acquired a HDC403-P23 UBC-C | DP | HDMI. Current setup
PC2 - Connected
- DP + HDMI
PC3 - Connected
- HDMI + HDMI + HDMI + USB
PC4 - Connected
- HDMI + HDMI + HDMI + USB
3 monitors (Output A + Output B + Output C)
The problem is that the 4 available back USB ports are not working, or at least, none of my PCs detect anything that I plugged in the back.
If I'm using the USB 3.0 port located at front (both USB 3.0 and USB-C), all devices are recognized for all computers - no issues.
This is what I tested so far:
- Power cycle the KVM device (disconnecting all HDMI, DPs and USBs, plus power connector for 30 mins - it didn't work.
- Switch computers between PCs slots (changing HDMI and USB connectors between PC2, PC3 and PC4 - it didn't work
- Test all USB devices individually, first using USB ports directly into each computer - all USB devices worked fine), and then using both, the USB 3.0 and UDB-C in the front of the KVM device - all USB devices worked fine.
Devices that I tested:
- Logitech BRIO 100 Web Cam
- Microsoft 2.4Ghx Transceiver for Mouse
- Jabra EVOLVE 65 Transceiver (audio)
- Corsair Gamin ST100 RGB Transceiver
What else can I do?
Nestor
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正式なコメント
Hi Nestor,
Thank you for your detailed description and the troubleshooting steps you’ve already taken — that’s very helpful.
Please try the following steps for further verification:
1. Check the power adapter:
Make sure you are using the original 12V/3A (or 12V/4A) power adapter that came with the KVM. Insufficient power can cause the rear USB ports to lose function.2. Check for USB power:
Plug in a USB device with an indicator light (e.g., wireless dongle or USB light) into the rear ports.If no power is supplied (no light), this may indicate a hardware or power issue.
If the device lights up but the PC still doesn’t detect it, the internal USB hub may not be initialized properly.
Looking forward to your reply.
Best regards,
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Hi TESmart,
I created a support ticket to evaluate the conditions of the rear USB ports. I connected several devices in those ports, and it looks like there is no power reaching out the ports. The same devices work fine in the front USB-A and USB-C ports.
It looks like there is a 7-layer cascade limit in the numbers of USB devices you can connect, which could impact these ports. I'm expecting reply from support to validate if this is the case and if there is any alternative to remediate the situation.
Regards,
Nestor
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Hi Nestor,
Thank you for your detailed feedback and for taking the time to test different devices — that information is very helpful.
You are correct that the USB specification defines a maximum of 7 cascading layers (including the host controller). This limitation is currently a known industry-wide constraint, not specific to our device.
Our KVM switch internally integrates several USB hub layers to manage multiple input devices and ports. When additional hubs or devices are connected externally, the overall chain may exceed the 7-layer limit, which can result in certain downstream ports (such as the rear USB ports) not being powered or detected by the host system.
Meanwhile, we recommend connecting high-priority or power-dependent USB devices (such as keyboards, mice, or dongles) to the front USB-A ports, which are managed through a more direct USB path to ensure stable performance.
Thank you again for your understanding and for bringing this to our attention — your input helps us improve future designs.
Best regards,
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