Does Windows remember HDMI devices?

[AlanRR]

Plug my large widescreen TV into my graphics card (hdmi connection) to use it as a 3rd monitor used to work just fine - after appropriate adjustment in ControlPanel/Displays.

Now everytime I plug my large widescreen TV in - all manner of odd effects take place. Some are - it alters the multiple dropdown choice to show desktop only on 2 and that of course blanks one of my 2 normally connected monitors. It pinches desktop icons from monitor 2 when it is monitor 1. All very weird.

BUT - when I plug in my small widescreen TV into the same HDMI socket on my GPU all works as expected. It waits for me to extend the desktop to include it and all works as expected.

The problem with my large widescreen TV manifests itself whether the connection is made to HDMI3 (legend next to socket) or HDMI2. No I have not tried HDMI1 because at this stage I am going bald (or maybe that should be balder).

The 2 TV's show as different names on Windows so there must be some feedback TV>PC and I am left to conclude that Windows is functioning different when it sees my large TV. Maybe a corrupt device profile if such a thing exists I don't know. If one does - can it be deleted or reset?

Help!!!

 

[Mellon Head]

I can't answer your main question as to why your large HDMI TV is malfunctioning, however, I can clear up one thing.

When you plug a video device into Windows (i.e. a monitor), there is definitely a conversation that takes place between Windows and the device, and Windows recognizes the capabilities of that device based on a profile information package that is transmitted form the device. I believe that a corresponding signature for the monitor is then stored in a Windows config file for access later. It saves the time of auto-negotiation when you plug the device in again. Windows just simply says "Aha! Monitor X is plugged in." and it works.

Sadly, I don't know where this profile is kept in Windows, or you could try to delete it.

I know that isn't the answer you were looking for, but I hope it helped clear things up a little bit. Perhaps a member with more knowledge in this area will happen by and give a better answer.

 

[AlanRR]

Yes - thanks - that confirms what I suspected - brilliant - thank you.

 

[AlanRR]

Research reveals we have a name for it - EDID - Extended Display Identification Data. Read from the display device over HDMI and stored in W7 registry. Enables the AV source device (pc) to understand lots of parameters of the display device it is feeding with AV data to ensure best possible experience and save human from entering data manually which could be wrong etc etc.

All research on EDID data and possible corruption seems to always assumes the corruption occurs in the device and describes many ways of rewriting EEPROM in device, but you need a lot of info and special software and GPU that's capable of rewriting EDID and a display device that permits remote rewriting of its EEPROM EDID data. Way too complex and impractical.

What is missing is a procedure to locate and delete registry based EDID data where I believe my problem lies. Apparently when a new device is connected EDID is requested once and stored forever so eliminating the need to repeat the exercise when the same device shows up again.

At the moment - reinstalling W7 seems the only way to rebuild the registry - and cause W7 to request fresh EDID for each display device it then encounters, and that for the time being is not worth the effort.

It would be so nice to be able to destroy all registry based EDID and get W7 to request again when necessary - but so far I cannot see any info as to how to achieve this......

 

[DavidE]

I don't know if this will help, but i see EDID registry info at
HKLM\SYSTEM\CurrentControlSet\Enum\DISPLAY\"name"\Device Parameters\EDID

If you know the "name" of the problem device, you could try deleting it from the registry,
then re-boot and attach the device to see if it will rebuild this info correctly.

I've never done this, i'm just guessing.

I would not do this without first creating a system image backup so i can restore if things go wrong.

Here is an example from my registry:

 

[NoN]

What's about the Devices Manager, when set to show hidden peripherals you should be able to see the details of each monitors. Could search in the registry using the class GUID after or uninstall from there?

 

[AlanRR]

DavidE - thanks for that info - got to same place in mine and found 5 entries in DISPLAY -

Default_Monitor had a BAD_EDID record in it - I assume this is a default sort of catch-all monitor entry for a fictitious device hence the lack of real EDID hence BAD_EDID entry.

the four other entries relate to 1) my LCD TV 2) my small LCD TV 3) my 1st dual monitor 4) my 2nd dual monitor - so all making good sense.

Found a neat little utility called DumpEDID from NirSoft - freeware utilities: password recovery, system utilities, desktop utilities follow the instructions to write results to a txt file and it will give you a human readable listing of the actual EDID data and what it means - quite interesting.

Now I am in a position to boldly delete the EDID data relating to the large LCD TV and see if it is the root cause of my problems. This may not happen too soon as I need to ensure reliable recovery is in place just in case this intimate surgery proves fatal and right now am very busy. Have a rebuild coming up soon so may try this just before final shutdown when I won't care if its fatal - but will in any event keep you posted.

NoN - tried Device manager idea but could not see any further devices when hunting for hidden peripherals - see above reply for interesting info. Thanks.

 

[Eric3742]

I would like to highlight 1 point.

----delete----

The problem with my large widescreen TV manifests itself whether the connection is made to HDMI3 (legend next to socket) or HDMI2. No I have not tried HDMI1 because at this stage I am going bald (or maybe that should be balder).

The 2 TV's show as different names on Windows so there must be some feedback TV>PC and I am left to conclude that Windows is functioning different when it sees my large TV. Maybe a corrupt device profile if such a thing exists I don't know. If one does - can it be deleted or reset?

Help!!!

There is one point you should take note and understand.

For example: USB port.

Whenever you plug a device to USB port-1, it will create a profile USB port-1, and will recognize the same device is plug in to the same USB port-1.

But if plug the device to USB port-2, then it will create a profile in USB port-2, and will recognize the same device is plug in to the same USB port-2.



So it is better to use the same HDMI port.

This is maybe how Windows works.



Regards
Eric.