Hello! I finally setup my L1Tech KVM but I’m having difficulty getting 4k resolution running at greater than 60hz. I’m using the new dual monitor/four computer HDMI 2.1 (MKAG-8KT3124) device. Right now I have a very simple single computer/single monitor setup while I try to figure out what isn’t working. The setup is as follow:
RTX 4090 HDMI 2.1 output
Cable Matters [Ultra High Speed HDMI Cert] – 6.6ft 3-pack
MKAG-8KT3124 HDMI 2.1 input
Club 3D Active HDMI 2.1 to DP1.4 – CAC-1335
Maxonar DisplayPort 2.1 Cable – 13ft
Acer Predator X27 DP1.4 input – X27bmiiphzx
When I bypass the KVM and connect the Club 3D active adapter directly to the RTX 4090 HDMI 2.1 output then I’ll get the full HDR/120hz connection though sometimes I have to unplug and replug the Club 3D power (perhaps to clear out some setting).
I think this narrows the issue down to two things:
The L1Tech KVM is somehow bottlenecking the data somewhere (likely due to some error in my configuration). I’d love for any ideas on where I may have messed up or what I can try.
or; the Cable Matters HDMI 2.1 6ft cable is garbage and doesn’t carry the advertised bandwidth. Does anyone have any experience with this brand?
Hmm 6 ft and 13 ft, pretty long for such a high bandwidth requirement. The cable matters isn’t necessarily a bad cable, the copper in the cable will lose strength over time, it might fix your issue to try a fiber optic HDMI cord so there is no signal degradation:
Thank you for sharing the idea; I’ll give it a shot. I noticed that when I skip the KVM and go Monitor → DP1.4 → Adapter → HDMI → 4090 then it will work at the intended bandwidth with the occasional need to replug the cable when its capped at 60hz. I find with the KVM it will very occasionally operate as intended but quickly revert back to being capped at 60hz. Hopefully the fiber optic cables will help (I’m getting the FIBBR Displayport cable also). If not then I think I may need a new monitor that supports native HDMI 2.1
Thanks again; I’ll report back when I test the fiber cables.
The KVM sees all connections as 1 long cable. The longer your cable, the more likely you will have signal problems with the KVM. For instance, PC 1 length + PC 2 length + monitor cable are are what you’re actually dealing with because the KVM has no repeater. So if PC 1 is 6.6ft, PC 2 is 6.6 ft, and the cable to your monitor is 13ft, that’s a pretty loooong cable in the eyes of the KVM. You definitely need some fiber optic cables since they’re so long
Thank you so much for all the help; this information has been extremely valuable. After testing the fiber cables it all seems to run much quicker (where before the screen would flash before eventually settling). I think I isolated the my problem to the active HDMI2.1 to DP1.4 converter (the Club-3D CAC-1335). The fiber cable flat out doesn’t even work with it (with a new FIBBR DP2.1 16ft cable). Its a black screen even without the KVM going from x27 → FIBBR DP1.4 → CAC-1335 → RTX 4090.
I know this is now out of the scope of the L1 KVM but I’m curious if you could advise on a quality HDMI to DP adapter.
(just to be sure) you are considering which end of the fiber optic cable is connected to your items right? Fiber optic cables only have 1 direction of traveling.
Yes, the source and display is connected correctly. The display works as intended when plugged in directly (x27 → FIBBR DP1.4 → RTX 4090[DP]) but fails completely when using the adapter (x27 → FIBBR DP1.4 → CAC-1335 → RTX 4090[HDMI]).
Yes, the power was appropriately supplied to the adapter but we can forget the converter now. I purchased a new monitor that supports HDMI 2.1 natively and now I’m using all HDMI 2.1 fiber optic cables. The setup is now:
The monitor does not receive any signal from the KVM. All cables work when the PC and monitor are directly plugged into each other. All cables are plugged in the correct orientation. This seems like this is the most natural way the KVM is supposed to work so now I’m at a complete loss.
try replacing this cable with a copper cable. we’ve had reports of 6 ft fibbr cables actually being worse than copper cables for whatever reason.
also try to press and hold the button next to the console port for 4 seconds. count 4 long seconds. maybe the kvm is remembering a bad setup from your previous monitor.
The copper HDMI 2.1 cables I have are the Cable Matters 6ft cables mentioned above. I tried every combination of the copper/fiber connections, running copper source to fiber, fiber to copper, fiber to fiber and copper to copper. The only combination that showed a signal was fiber source to copper after I reset the KVM as recommended but it was limited to 60hz. Attempting to increase that would yield no signal. Afterward I tried fiber to fiber and since then none of the combinations yield a signal anymore. I also tried moving the input to a different port but the results were the same. I also tried both input ports on the monitor (with HDMI Port 1 being an ARC connection) but again no results.
Thats wild. Email me wendell at level1techs.com and well setup a mail in rma for more testing. If if its actually bad itll be the first one. Is this single or dual monitor? If its dual monitor and both monitor rows arent working it has tk be something strange about your setup
Thank you, I’ll follow up on email. I can send you the HDMI cables I’ve been using also if that can help your diagnosis. I’m keeping it simple and only using a single monitor but since you mention dual monitor setups I just tried moving the inputs and outputs over to the second display. With all fiber connections I successfully got a signal that was limited to 30hz. Maybe this was foolish but I went over to the KVM to reset it just in case but now I don’t get any signals anymore.
Before I waste more of your time, I just wanted to make sure I’m resetting this correctly. A ~4 second hold will flash amber slowly while a ~4+ second hold will flash amber quickly. I tried both but I’m under the assumption that the quick flash is the correct one, right?
Thanks again for all the help, I really appreciate the time!
