ogsarg

Pin20 issue displaycable.

Discussion created by ogsarg on Jul 4, 2019

Hello, 

 

My displayport and hdmi of my RX580 is not working anymore. All the time i found it strange that there happens to be still current on my GPU even when the pc was turned of. After some research i found that some people in the past had issues with the pin20 on the display cable causing the gpu to suffer while booting and even eventually die. 

The pin 20 is used for powering an adapter without current supply.

 

After having a look at my cable with my tester i found out that pin 20 was connected on both sides and that my monitor 

(ASUS VG248QE) was sending -1.1V to my GPU between pin 20 and GND while my GPU is constructed to give +3.3V over pin20 and GND, so yes a minus on a plus this cannot be good.I just wonna ask to people of amd if this can give a conflict and cause the GPU to suffer. 

 

Should i use a cable without pin20 connected? 

Should i only use a vesa certificated cable? 

 

Pls help me out i will be very thankfull. 

 

Bart. 

 

Some info in found: 

link: http://monitorinsider.com/displayport/dp_pin20_controversy.html

The Problem

The problem with this arrangment is that one should never ever connect the DP_PWR of the source to the DP_PWR of the sink: it's impossible for both pins to have exactly the same voltage, so connecting them together would effectively result in a short circuit condition.

In addition, if, your GPU is powered off, while your monitor is powered on, you get a problem that's commonly called 'backdrive': a sneaker path that feeds electrical compoonents in the GPU even though nothing is supposed to have power. This can result in your GPU behaving erratically when trying to power up. In some cases, it can even damage the GPU.

This is why regular DP cables should never have a wire between pin 20 of boths sides of the cable.

The official DisplayPort FAQ used to say the following

Q: Why isn’t there a wire on pin 20 (POWER) on the standard external DisplayPort cables?

A: The reason power isn’t included in standard cables is because both source and sink devices are designed to provide power. Captive, attached cables often include the power wire. If it is desired, for example, that a particular source device utilize the power available from the mating sink device, then that Source device could include an attached or dedicated cable that carries the DisplayPort power signal. Same could be applied to a sink device.

 

 

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