VGA Female/Female Gender Changer and resolution problem.

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VGA Female/Female Gender Changer and resolution problem.

Postby hack3rcon » 2019-08-23 07:45

Hello,
I'm using a VGA Female/Female Gender Changer like https://www.bhphotovideo.com/c/product/1020450-REG/kramer_ad_gf_gf_15_pin_hd_f_f_gender.html and my Desktop resolution is changed to the Half monitor. The monitor show me a "not optimum mode" message.
Any idea to solve it?

Thank you.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby p.H » 2019-08-23 08:14

What do you mean by "half monitor" ?
Why do you need to use this adapter ? To connect two male-male VGA cables together ?
The I²C DDC2 signalling which allows to detect the monitor capabilities over a VGA link may be altered by overly long links and multiple junctions.
The I²C bus was primarly designed to interconnect chips on the same printed circuit board or in the same device, not separate devices through long cables.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby hack3rcon » 2019-08-23 08:31

p.H wrote:What do you mean by "half monitor" ?
Why do you need to use this adapter ? To connect two male-male VGA cables together ?
The I²C DDC2 signalling which allows to detect the monitor capabilities over a VGA link may be altered by overly long links and multiple junctions.
The I²C bus was primarly designed to interconnect chips on the same printed circuit board or in the same device, not separate devices through long cables.

I meant was my Desktop resized to the half of monitor size.
I want to plug another system to my monitor. Something like KVM switch.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby p.H » 2019-08-25 07:14

As mentionned in https://en.wikipedia.org/wiki/Display_Data_Channel#Disabling_DDC, KVM switches sometimes break DDC detection.
But I still do not understand why you need a gender changer.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby hack3rcon » 2019-08-25 11:36

I have two systems and one monitor. I bought a VGA Female/Female Gender Changer and plugged my monitor cable to it. I want to plug the systems cable manually when I need each of them.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby p.H » 2019-08-25 12:11

IIUC, you use the F/F adapter to connect two M/M VGA cables together ?
If you have multimeter, you can check that all 15 pins are connected between both sides of the adapter and the cables.
Also, what if the total length of the two cables connected together ?
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby nulix » 2019-08-27 16:16

I'm just here, lurking, wayting for the pics of your setup so that we all can make sense of this :)
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby phenest » 2019-08-27 16:52

hack3rcon wrote:... and plugged my monitor cable to it. I want to plug the systems cable manually when I need each of them.

This makes no sense. Both ends of the cable have to be male because both monitor and video card require it. So why do you want one end to be female?

2 systems and 1 monitor is not uncommon, but surely you just need to unplug one cable from the monitor and plug in the other cable to switch systems?

As nulix asked, a photo would clarify what you're doing.

If you are, in fact, connecting 2 cables together, then that is your problem. The VGA signal is analogue and if the cable is too long, you get signal degradation and the monitor is trying to understand the signal it's getting.
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Re: VGA Female/Female Gender Changer and resolution problem.

Postby p.H » 2019-08-27 20:45

phenest wrote:This makes no sense. Both ends of the cable have to be male because both monitor and video card require it. So why do you want one end to be female?

One VGA cable attached to the monitor and two VGA cables attached to the two computers. the F/F adapter is used to connect the monitor cable with either computer cable. Kind of poor man's VGA switch. This is more convenient than moving cables at the back of the computers or the monitor.

phenest wrote:If you are, in fact, connecting 2 cables together, then that is your problem. The VGA signal is analogue and if the cable is too long, you get signal degradation and the monitor is trying to understand the signal it's getting.

Only RGB signals are analog. The H/V sync and monitor identification (DDC) signals are digital, not analog. However they may also be degraded by too long cables and/or too many connector junctions.
2) The monitor showing the message "not optimum mode" suggests that the computer uses a low resolution mode probably because it cannot identify the monitor capabilities due to DDC communication failure. xrandr would confirm it.
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