Projector does not auto detect screen resolution over VGA

[DavR]

Bit of a conundrum for you guys, regarding auto setting screen size and apect via VGA.

 

We have a PC connected to a projector in one of our halls, both a few years old but still quite serviceable. We're using a single VGA out from the PC, into a VGA splitter, to a monitor and also the projector. HDMI is not an option, VGA is the only line available without running new cables.

 

When we start up PC first, then projector, the projector detects the PC input correctly, and shows it at the right size and aspect. However, if we start up the projector first and then the PC afterwards, something gets missed and the screen size is not detected, we get a distorted image on the projector. This is fixed by changing the channel on the remote, or using "Source Search" to select the correct source.

 

Is something wrong in our setup, or, do we think this is the system behaving as expected? I did wonder whether maybe the PnP pin somewhere on the VGA run is busted, but then, the monitor is using the PnP port, not the projector, so that shouldn't come into play. Both PC and projector get switched off at the mains after use, so there is a permanence issue. I wondered if the onboard battery on either could be dead, but then, other settings are remembered, so perhaps not.

 

Any ideas how I can get round this?

[Brax]

Have you tried adjusting the display resolution in the windows settings to something like 1024 x 768? (Assuming it’s windows) When it comes to lower resolutions usually the source the laptop in this case needs to be able to match the maximum supported resolution of the projector. It sounds like it attempts to pickup the signal and fails.

Edited May 12, 2025 by Brax

[DavR]

I'm not sure what the maximum resolution is on the projector, it should be fairly capable though. When it has successfully detected the right screen size, it displays 1280x1024 quite happily.

 

Having said that though, it could be an idea throwing it onto a lower resolution and seeing if it copes better. We used to have a tiny monitor on it which maxed out at 1024x768, and I don't remember it giving us these problems back then.

[DavR]

Nah, that didn't do it. Not a bad suggestion though. Low res behaves the same way as higher res.

 

To rule out the splitter and the monitor, I ran VGA direct from the PC to the projector (well, through the infrastructure cabling). This way, gave me full resolution 1280x1024, but, at a really small picture size that I couldn't expand! Baffled 😂

[Brax]

14 hours ago, DavR said:

Nah, that didn't do it. Not a bad suggestion though. Low res behaves the same way as higher res.

 

To rule out the splitter and the monitor, I ran VGA direct from the PC to the projector (well, through the infrastructure cabling). This way, gave me full resolution 1280x1024, but, at a really small picture size that I couldn't expand! Baffled 😂

I have a feeling it may be the splitter in that case. However,

I’d rule out all hardware first. VGA lead, splitter etc. Maybe try a different PC or laptop if able. 

Edited May 13, 2025 by Brax

[chazzy2501]

why do the monitor and projector share a VGA? can the monitor at least not be run from hdmi or DP?

 

The VGA splitter will only allow EDID to one device. (so you may have to switch outputs.)

 

 

[Brax]

6 minutes ago, chazzy2501 said:

why do the monitor and projector share a VGA? can the monitor at least not be run from hdmi or DP?

 

The VGA splitter will only allow EDID to one device. (so you may have to switch outputs.)

 

 

Yeah it may need a HDMI monitor. For our setup the monitor was using HDMI and had a splitter for two projectors for the hall. Never failed.

Edited May 13, 2025 by Brax

[Oaktech]

It's almost always the splitter many either don't support DDC or only pass it back to the host on one port.

 

When you run it straight into the projector and it gives you 1280x1024 can you try the picture size button on the projector remote for something like 'full' or 'native'

 

I've solved this with a VGA EDID Emulator - they aren't cheap - between £25 and £125 depending on features, but it's often worth it to stop all the 'Sir, the projector's gone weird again' calls.

 

https://www.blackbox.co.uk/gb-gb/page/25834/Resources/Technical-Resources/Black-Box-Explains/AV/EDID-Emulation/

 

 

[DavR]

The splitter isn't faulty as such, I've swapped it out for another and the results are the same. But arguably it is the weak link, yes. One port is marked as the "Plug and Play" port, which makes sense re DDC only working on one port. I've been running it with the monitor on that port, because the other way round, I get a small image on the projector, and a distorted one on the monitor. This was round, we get a decent image on the monitor, but, sometimes, you need to redetect on the projector to get the proper image! There's no winning down that route, it seems.

 

We've been running VGA and splitter for this long purely for reliability - a split VGA signal (used to) work out of the box every time, no settings required - where going duplicate display requires additional settings, introducing extra problems. 

 

I can try running it as duplicate display, VGA for projector and a secondary for the monitor, but I'll have to stick a graphics card in the PC. My concern then is that the detected VGA will show up very small, as it did when I ran VGA direct, and presumably DDC took hold between projector and PC, and I couldn't stretch that image to fit the screen. Dunno why that's happening, when going through the splitter the image fills the screen. Weird. 

[Koldov]

Just a couple of thoughts...

 

Maybe when the projector is on first, the gfx in the computer picks up the signal when it is started  and negotiates a setting....

 

...and when the computer is on first the graphics are unaware of the connection to the projector, so no negotiation (this may then happen when you press the auto/input/scan)... 

 

...also, when the DDC is being passed between the monitor and the computer, duplicating the screen would duplicate the monitors settings to the projector (as no DDC on the run to/from the projector).

 

Just interested to know if there is any GFX GUI panel on the computer and what it picks up (if anything) for dual display, maybe there is a panel fit/fill option in there?

Edited May 13, 2025 by Koldov

[DavR]

2 hours ago, Koldov said:

Maybe when the projector is on first, the gfx in the computer picks up the signal when it is started  and negotiates a setting....

 

...and when the computer is on first the graphics are unaware of the connection to the projector, so no negotiation (this may then happen when you press the auto/input/scan)... 

Yes, although the other way round I think. If projector is on first, then PC boots into already on projector, projector is unaware of change, so no negotiation takes place re screen settings. Incorrect image occurs.

 

If PC is on first, then projector turns on, projector detects source during startup and shows correct image.

 

Quote

...also, when the DDC is being passed between the monitor and the computer, duplicating the screen would duplicate the monitors settings to the projector (as no DDC on the run to/from the projector).

 Yup.

 

Quote

Just interested to know if there is any GFX GUI panel on the computer and what it picks up (if anything) for dual display, maybe there is a panel fit/fill option in there?

 

Might be something extra in the GFX settings when I try dual displays, you never know. An extra setting to check when I get that far!

[Koldov]

We have a ridiculous set-up for our hall projector... all VGA as massive run up the wall and across the ceiling! It was set-up when everything was VGA and I have no inclination/need to mess with it.

 

It was set-up to be a monitor and projector, just running from a PC. We had an old ATEN VS-102 powered video splitter and it worked OK (can't remember which connection was on the DDC though).

 

Then all the teachers (including SLT) decided it was easier for them to bring their laptop to the hall rather than saving their document on the staff drive and using the computer. So, I had to find a way to get the PC to the projector and the monitor, but also the laptop to the projector. Oh and audio from either into the amplifier or powered speakers!

 

To say it's a bit of a spaghetti jungle of cables inside the cabinet is an understatement... but if iirc it includes a passive Y cable splitter from PC and laptop going into the 'in' of the powered splitter... then one of the 'outs' to the monitor and the other to the projector (I 'think', although now I'm sure I had to change things around and the solution didn't actually make sense)! The audio is even more convoluted and if I'm honest I'm not sure how, but at some point when I was swapping cables it just worked, so I left it well alone... Obviously we do get some issues when the PC and a laptop are both on.

 

I also get some similar issues as yours with classroom projectors (but no splitters)... because the teachers want to duplicate instead of extending (because that's too complicated, right?!). As their laptop screen is something like 1440x900 or higher, the projector does weird things (letterboxing and so on) and I can't be bothered to teach them about the GFX GUI. I just set their laptop screen to a basic 1024x768 when connected to the projector, which makes everything on the board readable and everybody (apart from one... 🤬) happy and it snaps back to the proper resolution on the laptop when unplugged.

Edited May 13, 2025 by Koldov

[Koldov]

25 minutes ago, DavR said:

Yes, although the other way round I think. If projector is on first, then PC boots into already on projector, projector is unaware of change, so no negotiation takes place re screen settings. Incorrect image occurs.

 

If PC is on first, then projector turns on, projector detects source during startup and shows correct image.

 

Yeah, actually that does make sense 😀 I guess depending on the set-up and which end has to read the settings in the signal!

 

If the projector doesn't auto sense the signal and it's not set-up to auto adjust etc. Have you gone through all of the projector settings for something like that?

[DavR]

I finally got a chance to test this with an extra graphics card in place, to replace the VGA splitter. After a brief suggestion that it might resolve our issue, no change 🙄

 

Our outputs are now VGA (projector) and DVI (monitor), with duplicate display set on the PC:

• If I turn PC on first, then the projector, duplicate display works perfectly
• If I turn on projector first, then PC, the projector doesn't detect the VGA input correctly, and I have to do a scan using the remote control to fix it.

It's a minor issue in the grand scheme of things, but, because staff don't realise, they try and re-size the projector screen to match, and always b****r it up.

 

There is a second VGA line up to the projector, I may experiment with that when I can get the ladders out during the summer, just in case the PnP line in VGA1 is damaged. Til then, I'll have to make do with a big Dymo tape sticker that says "PRESS SOURCE SEARCH" to fix display issues.....

[DavR]

On 16/06/2025 at 17:59, DavR said:

Til then, I'll have to make do with a big Dymo tape sticker that says "PRESS SOURCE SEARCH" to fix display issues.....

 

The Dymo sticker fell off....

 

FFS!

[chazzy2501]

if the projector has a serial port (or better an Ethernet) you could script a telnet command at login to do a "source search" but what an effort!