3 ms·

So these guys [1] mention something similar where HDMI from a TV is backfeeding 40-50 volts into a cable box. This could be because of many things from electri

by bb88 2y ago

So these guys [1] mention something similar where HDMI from a TV is backfeeding 40-50 volts into a cable box. This could be because of many things from electrical outlet wiring to power supply issues on the monitor to a bad component on the monitor giving a high voltage, or the monitor is badly grounded, etc, etc. I read the original thread but it doesn't look like you've measured the voltage at the HDMI port wrt motherboard ground. I think we're assuming it's 5 volts, but it could be higher, and it could have shorted (or weakened) a component on your motherboard. And that would explain why a 100 ohm resistor didn't give a meaningful voltage drop. If you need an isolation solution, Amazon sells a 50ft fiber optic one way HDMI cable [2]. The thing I don't know is if there's any actual copper to provide power over the link. There are other options which transmit the HDMI signal over pure multimode fiber as well [3]. Or you can go with a DP KVM, since you're on L1T, they sell a few DP models. I have one I purchased from L1T, and I like it a lot. Definitely though I would check out the outlets to make sure they were wired correctly. Incorrectly wired outlets because someone tried to DIY it in the US is absolutely a problem. [1] https://www.avsforum.com/threads/hdmi-cable-backfeeding-voltage-from-tv-to-cable-box.1345211/ https://www.avsforum.com/threads/hdmi-cable-backfeeding-volt... [2] https://www.amazon.com/HDMI-FURUI-HDCP2-2-18Gbps-Subsampling/dp/B077D37MT3?th=1 https://www.amazon.com/HDMI-FURUI-HDCP2-2-18Gbps-Subsampling... [3] https://fibercommand.com/products/8k-fiber-plugs?gQT=1 https://fibercommand.com/products/8k-fiber-plugs?gQT=1

starslab 2y ago
I already own one of those fiber-hdmi cables. Brilliant, but sometimes doesn't interoperate with DVI devices using passive DVI -> HDMI adapters. I've no idea if it has any copper conductors for HDMI power, though one end is labelled for the source and one for the display, suggesting that however it's designed it's not bi-directional. I'd love a DisplayPort KVM, but not every device that comes across my bench has a DisplayPort output, and those few that have DisplayPort but no HDMI can be accommodated with one of those commodity DisplayPort -> HDMI adapters. This situation is actually getting worse over time, not better, as many modern devices and laptops are skipping DisplayPort in favor of USB-c alt-mode. This issue has actually been going on through a monitor change on my testbench. It has happened with a Samsung SyncMaster 204T though my KVM switch, an HP ZR24w through my KVM switch, and the ZR24w directly connected. I don't think this is an issue with the rest of my equipment. This electrical was done about 15 years ago, by a ticketed electrician. One of those $5 plug testers indicates all is well, and I have no reason to believe there's any issue here. By almost pure coincidence, I have an MSI PRO X870-P motherboard on order. I'm looking forward to seeing if this same 3V3 leakage issue is present on this board too.

by bb88 2y ago

starslab 2y ago

I already own one of those fiber-hdmi cables. Brilliant, but sometimes doesn't interoperate with DVI devices using passive DVI -> HDMI adapters. I've no idea if it has any copper conductors for HDMI power, though one end is labelled for the source and one for the display, suggesting that however it's designed it's not bi-directional. I'd love a DisplayPort KVM, but not every device that comes across my bench has a DisplayPort output, and those few that have DisplayPort but no HDMI can be accommodated with one of those commodity DisplayPort -> HDMI adapters. This situation is actually getting worse over time, not better, as many modern devices and laptops are skipping DisplayPort in favor of USB-c alt-mode. This issue has actually been going on through a monitor change on my testbench. It has happened with a Samsung SyncMaster 204T though my KVM switch, an HP ZR24w through my KVM switch, and the ZR24w directly connected. I don't think this is an issue with the rest of my equipment. This electrical was done about 15 years ago, by a ticketed electrician. One of those $5 plug testers indicates all is well, and I have no reason to believe there's any issue here. By almost pure coincidence, I have an MSI PRO X870-P motherboard on order. I'm looking forward to seeing if this same 3V3 leakage issue is present on this board too.