Start with a two-minute triage
This guide follows GL.iNet's published KVM troubleshooting pages as of 30 October 2026. We have not reproduced these faults on our own hardware. GL.iNet's first instruction for a blank remote screen is to log in to the KVM and set the transfer mode to Direct (Settings > Video > Transfer in the FAQ). It then says to check the monitor icon in the bottom-right corner of the console for a 'No HDMI signal' message. [1]
That message helps you split the problem in two. If the console reports no HDMI signal, look at cables, ports and the target PC. If the console has a signal but the browser view stays black, look at the transfer mode and browser instead. The Comet Pro home screen also shows keyboard and mouse, HDMI and USB status at the bottom, so you can check from the device itself. [8]
| What you see | Most likely area | First check |
|---|---|---|
| Console says 'No HDMI signal' | Cable, port or adapter | PC video output into Comet Pro HDMI IN, not HDMI OUT [1] |
| Signal present, browser view black | Transfer mode or browser | Set transfer to Direct; try Chrome, Firefox or Edge; disable WebRTC-blocking extensions [1] |
| Video after login, black at boot | BIOS output on another port | Move the KVM to the primary output or use a splitter [3] |
| Picture garbled or out of range | Resolution or EDID | Stay at or below 2560x1440 at 60 Hz, no interlaced modes [2] |
| Black after the PC sits idle | Sleep or power settings | Wake the PC, then use Mouse Jiggle or Wake-on-LAN [1][7] |
Cables, ports and connection order
GL.iNet's quick setup order is: connect power, run an HDMI cable from the Comet Pro's HD IN port to the target PC's HD OUT, connect the Comet Pro's USB-C port to a USB port on the PC, then join Ethernet or Wi-Fi. A second HDMI cable from the Comet Pro's HD OUT to a local monitor is optional. [4] The box includes two HD cables, a USB-A to USB-C cable and a USB-C to USB-C cable. [8]
GL.iNet's troubleshooting page names three cabling faults. First, aging cables, oxidised connectors or internal breaks can interrupt the signal, so swap in a known-good cable. Second, the connection may be wrong. On a desktop, HDMI IN must go to the graphics card or motherboard output, fully seated; if the PC has several outputs, try another. On Comet Pro, the PC must go to HDMI IN, because HDMI OUT gives no console signal. Third, adapter direction matters. A VGA-to-HDMI adapter can work, but GL.iNet says an HDMI-to-VGA adapter does not carry video properly and leaves a blank screen. [1]
- Re-seat both ends of the HDMI cable and confirm it runs PC HDMI OUT to Comet Pro HDMI IN.
- Swap the HDMI cable for a different, known-good one before changing any settings.
- If the PC has both integrated and dedicated graphics, use the dedicated GPU port when a card is installed. [1]
- Keep the USB-C cable connected to the PC so keyboard and mouse status shows on the Comet Pro. [4][8]
Transfer mode and browser checks
The Comet Pro console offers four transfer modes: WebRTC, WebRTC (FEC), WebRTC (Native) and Direct. GL.iNet describes Direct as the lowest-latency, lossless option, and notes that Direct transfer has no sound. [5] Use Direct while troubleshooting. Once video works, switch back to a WebRTC mode if you need audio.
If the console reports a signal but your view is black, GL.iNet suggests trying another browser (Chrome, Firefox or Edge). It also says to disable extensions that interfere with WebRTC, such as leak-protection tools, and to confirm in the browser's privacy settings that WebRTC connections are allowed. [1] A privacy extension on your laptop can black out the stream even when the KVM is fine.
Resolution and EDID limits
EDID is the VESA-standard data a display reports to a computer, including its maximum resolution and refresh rate. The computer uses it to choose an output signal. GL.iNet's EDID tutorial lists these limits: maximum 2560x1440 at 60 Hz, with 2560x1600 at 60 Hz given as unsupported; maximum refresh 60 Hz, with 60 fps or lower recommended above 1920x1080; and no interlaced resolutions, which it says cause abnormal display. [2]
GL.iNet says the default EDID suits most scenarios and does not usually need changing. Its blank-screen FAQ lists EDID as a rare cause, giving a Linux system paired with an ASUS monitor as an example combination that can blank the screen. [1][2] If you do need a change, for example for UEFI or BIOS work or a specific resolution, choose a preset under Settings > Video > EDID. For a custom profile, switch to Customize, paste an EDID code and click Set Custom. GL.iNet says you can use no more than two EDID code blocks, and that the profile needs basic audio support or the PC may not offer a sound device. [2] The console guide adds that if the screen does not refresh after an EDID change, you should restart the controlled device. [5]
For Linux hosts that boot to a console, GL.iNet's FAQ gives a Proxmox VE example. Edit /etc/default/grub, add quiet gfxpayload=text nomodeset to GRUB_CMDLINE_LINUX_DEFAULT, set GRUB_GFXMODE to a modest mode such as 1024x768, then run update-grub. [1]
| Setting on the PC | GL.iNet guidance | Action |
|---|---|---|
| 2560x1440 at 60 Hz | Maximum supported [2] | OK; drop lower if the image is unstable |
| 2560x1600 at 60 Hz | Unsupported example [2] | Lower to 2560x1440 or 1920x1080 |
| Above 60 Hz | Maximum refresh is 60 Hz [2] | Set the display output to 60 Hz |
| Interlaced mode (for example 1080i) | Causes abnormal display [2] | Use a progressive mode |
| Custom EDID profile | Max two code blocks; needs basic audio [2] | Restart the PC if the screen does not refresh [5] |
The target PC: sleep, drivers and the BIOS screen
A sleeping PC sends no video. GL.iNet's checklist says to confirm the PC is fully on and not asleep or hibernating, and to wake it with local controls if needed. It also lists missing or corrupted graphics drivers as a cause, fixed by updating or reinstalling them on the PC. [1] To prevent idle sleep, GL.iNet's KVM FAQ describes Mouse Jiggle, which simulates periodic mouse movement. Wake-on-LAN sends a magic packet to the PC's MAC address to wake it. [7] In the console, Wake-on-LAN sits under Toolbox > Wake-on-Lan. If you have the separately sold ATX board, power controls are under Accessories > ATX Power. [5]
If you get video in the operating system but not during boot, the cause is usually the display port, not the KVM. GL.iNet says the BIOS normally outputs only to the primary monitor, and most graphics cards and motherboards prefer DisplayPort over HDMI at startup. On a laptop, the built-in screen is primary, so an external KVM cannot render the BIOS. On a desktop, GL.iNet suggests connecting the KVM to the port the PC treats as primary, or using a 1-to-2 HDMI splitter (not included) to send the primary signal to the KVM too. The same limit applies in Windows PE unless you add display drivers to it. [3]
Firmware: check the version before deeper work
To check firmware, click the firmware version in the upper-right corner of the KVM console. If a newer version exists, the pop-up offers an online upgrade. Under Update Settings you can also do a local upgrade with a file from GL.iNet's Firmware Download Center. GL.iNet warns that the Beta Program can be unstable, so stay on release firmware while troubleshooting video. [6]
Record the firmware version before and after any upgrade. If video stops right after an update, that version number is the most useful detail for a support ticket.
When to stop and contact GL.iNet or the seller
GL.iNet's BIOS FAQ suggests a useful isolation test: connect a separate monitor to the same output. If that monitor also shows nothing, the problem is the PC's output on that port rather than the KVM. [3] Run the reverse test too. Feed the Comet Pro from a different, known-good HDMI source, such as another laptop, using a cable you have just seen working.
If the Comet Pro still reports no HDMI signal after all of these checks, the fault more likely lies with the unit. The checks are: Direct mode, the correct HDMI IN port, a known-good cable, an awake PC sending video to a monitor, a resolution within the limits above, the default EDID, and current release firmware. GL.iNet's product overview says a factory reset is done by holding a pin in the reset pinhole for 8 seconds while the KVM is powered on. [8] For anything the checklist does not solve, GL.iNet's troubleshooting page points to its community forum and its Contact us page. [1] Return and warranty terms depend on where you bought the unit. We did not review GL.iNet's warranty terms for this guide, so contact GL.iNet or your seller with your evidence.
- Include the firmware version, the PC model, the output port used, the resolution, and the result of each test in your support request.
- Note whether the console icon says No HDMI signal, or shows a signal with a black browser view. GL.iNet treats these as separate cases. [1]
| Test | Result | What it points to |
|---|---|---|
| Same PC port to a plain monitor | No picture | PC, port or GPU setting, not the KVM [3] |
| Same PC port to a plain monitor | Picture | Cable, KVM settings or KVM hardware |
| Another HDMI source into Comet Pro HDMI IN | Still no signal | Likely Comet Pro hardware; reset, then contact support [1][8] |
| Another HDMI source into Comet Pro HDMI IN | Video appears | Original PC's output, resolution or EDID |
Questions before you decide
Why does my Comet Pro say No HDMI signal when the cable is plugged in?
GL.iNet notes that Comet Pro has two HDMI ports and that the PC's video output must go to HDMI IN. A cable in HDMI OUT produces no signal on the console. After that, GL.iNet points to faulty or aging HDMI cables and the wrong adapter direction as common causes.
What is the highest resolution the Comet Pro can capture?
GL.iNet's EDID tutorial gives a maximum of 2560x1440 at 60 Hz and lists 2560x1600 at 60 Hz as unsupported. It also recommends 60 fps or lower above 1920x1080 and says interlaced resolutions cause abnormal display.
Why can I see Windows but not the BIOS through the KVM?
GL.iNet says the BIOS usually outputs only to the primary monitor, and many desktop boards prefer DisplayPort over HDMI at startup. On laptops the built-in screen is primary, so an external KVM cannot show the BIOS. On a desktop, connect the KVM to the primary output or use an HDMI splitter.
Should I change the EDID setting first?
No. GL.iNet says the default EDID suits most scenarios and lists EDID as a rare cause of blank screens. Try Direct transfer mode, cabling, the PC's power state and drivers first. If you do change EDID, GL.iNet says to restart the controlled device if the screen does not refresh.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- GL.iNet KVM Docs: Remote screen goes blank or shows no HDMI signal Accessed 30 Oct 2026
- GL.iNet KVM Docs: How to set EDID for KVM Accessed 30 Oct 2026
- GL.iNet KVM Docs: Remote screen does not show the BIOS interface Accessed 30 Oct 2026
- GL.iNet KVM Docs: GL-RM10 Quick Setup Accessed 30 Oct 2026
- GL.iNet KVM Docs: GL-RM10 Console Guide Accessed 30 Oct 2026
- GL.iNet KVM Docs: Firmware upgrade Accessed 30 Oct 2026
- GL.iNet KVM Docs: Quick FAQs about GL.iNet KVM Accessed 30 Oct 2026
- GL.iNet KVM Docs: GL-RM10 Product Overview Accessed 30 Oct 2026
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