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USB Keyboard "skips" characters after installing RX580

Joined
Sep 22, 2011
Messages
321
Motherboard
Thinkpad T61-Clover
CPU
T9300
Graphics
NVS 140m, 1280x800
Mac
MacBook Pro
I resolved an annoying "character skipping" behavior of my USB keyboard by separating my CPU power (8-pin) and PCI-e power (8-pin) onto separate PSU "rails." Details are below. I'm sharing to help others who might observe this and to ask if anyone else has observed this.

After I installed a Sapphire Pulse RX580 in my old Socket 1156 system described here, my USB keyboard would occasionally "skip" characters. The skipping came at what appeared to be random times. By "skip," I mean that some of my typed characters were not actually typed. This problem did not happen when I had an NVidia 9800GT graphics card installed.

Since this seemed to be clearly a power problem (problem only started after upgrading to the more power-hungry RX580), I examined my PSU (a SeaSonic Focus 750W Gold) and found that I had both the CPU (8-pin power cable) and RX580 (8-pin power cable) connected to the same "rail." My PSU is semi-modular with permanent CPU and PCI-e power cables on one rail and modular peripherals/PCI-e sockets on a separate rail. I disconnected the permanent 8-pin PCI-e power cable from my RX580 (leaving it disconnected) and replaced the RX580 power with a modular PCI-e power cable connected to the second rail of the PSU.

I am no longer experiencing the skipped characters after making this power cabling change.

Apparently, having the CPU and RX580 powered from the same PSU rail created enough system noise to affect USB performance.
 
Joined
May 15, 2016
Messages
5,078
Motherboard
GIGABYTE Z170M D3H
CPU
i5-6500
Graphics
RX 480
Mac
iMac
I resolved an annoying "character skipping" behavior of my USB keyboard by separating my CPU power (8-pin) and PCI-e power (8-pin) onto separate PSU "rails." Details are below. I'm sharing to help others who might observe this and to ask if anyone else has observed this.

After I installed a Sapphire Pulse RX580 in my old Socket 1156 system described here, my USB keyboard would occasionally "skip" characters. The skipping came at what appeared to be random times. By "skip," I mean that some of my typed characters were not actually typed. This problem did not happen when I had an NVidia 9800GT graphics card installed.

Since this seemed to be clearly a power problem (problem only started after upgrading to the more power-hungry RX580), I examined my PSU (a SeaSonic Focus 750W Gold) and found that I had both the CPU (8-pin power cable) and RX580 (8-pin power cable) connected to the same "rail." My PSU is semi-modular with permanent CPU and PCI-e power cables on one rail and modular peripherals/PCI-e sockets on a separate rail. I disconnected the permanent 8-pin PCI-e power cable from my RX580 (leaving it disconnected) and replaced the RX580 power with a modular PCI-e power cable connected to the second rail of the PSU.

I am no longer experiencing the skipped characters after making this power cabling change.

Apparently, having the CPU and RX580 powered from the same PSU rail created enough system noise to affect USB performance.
That is odd. Balancing is important especially when using higher percentages of your available power but a 750 watt supply should be able to handle the load. Seasonic are highly rated PSUs too so that’s weird to hear about this. How much power does the system pull without the RX card? The RX pulls 180 watts but 75 watts may come from the PCI slot.
 
Joined
Sep 22, 2011
Messages
321
Motherboard
Thinkpad T61-Clover
CPU
T9300
Graphics
NVS 140m, 1280x800
Mac
MacBook Pro
That is odd. Balancing is important especially when using higher percentages of your available power but a 750 watt supply should be able to handle the load. Seasonic are highly rated PSUs too so that’s weird to hear about this. How much power does the system pull without the RX card? The RX pulls 180 watts but 75 watts may come from the PCI slot.
It's a Xeon X3460 rated at 95W TDP. I wasn't even overclocking it (yet). I have to confess that the idea to split the CPU and RX580 onto different rails came from a Seasonic how-to post that I found when I was researching power issues. I don't know enough about PSUs to explain it.
 
Joined
Sep 22, 2011
Messages
321
Motherboard
Thinkpad T61-Clover
CPU
T9300
Graphics
NVS 140m, 1280x800
Mac
MacBook Pro
That is odd. Balancing is important especially when using higher percentages of your available power but a 750 watt supply should be able to handle the load. Seasonic are highly rated PSUs too so that’s weird to hear about this. How much power does the system pull without the RX card? The RX pulls 180 watts but 75 watts may come from the PCI slot.
Thank you for your response. I now have an open case with Seasonic to determine whether the PSU is defective. I believe you are correct that the 750W Gold PSU should have no problem powering the CPU and the RX580 from the same "rail" (if I'm using the correct terminology). As is, if I needed to power a second PCI-e device (using the PSU's permanently connected 8-pin PCI-e power cable), I would be unable to do so. I'll add details to this thread if I learn anything that will help others.
 
Joined
Sep 22, 2011
Messages
321
Motherboard
Thinkpad T61-Clover
CPU
T9300
Graphics
NVS 140m, 1280x800
Mac
MacBook Pro
@Gigamaxx , Seasonic tech support wants me to move the power supply to another system with another graphics card to prove that it is the power supply and not something else that is causing the problem. According to them, it's not sufficient evidence that I can fix/duplicate the problem by switching between the two PCI-e power sources on the PSU. If the PSU is the problem, I would pay for return shipping to RMA the unit. Their request is more than I'm willing to do, so I'm just going to be happy that everything works as-is.
 
Joined
May 15, 2016
Messages
5,078
Motherboard
GIGABYTE Z170M D3H
CPU
i5-6500
Graphics
RX 480
Mac
iMac
It is weird that the provided 6-8pin is on the same rail as the CPU and Mainboard. You would think by default they would balance the power cords that are default or existing and not make users use the add on cords to balance.
 
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