ATC-605: No Display on new HDMI monitor if old VGA monitor is disconnected

I recently purchased an LG 27UL650 UHDI monitor. Old monitor was/is a Samsung 2000 Syncmaster. Old monitor is plugged into VGA port of ATC-605. I plugged new monitor into HDMI port and display is fine. In Display Settings, I set new monitor to primary. I went to Devices and Printers in Control Panel and selected "Remove Device". I physically disconnected the old monitor from the ATC-605 VGA port. Shut down, restart. I hear 1 beep. New monitor flashes "HDMI.." signal, so there is some output to it from the computer, but then screen goes black. I don't know how far the boot process has gone. Now....I have turned off old monitor and removed the power cord. With computer shut down, I plug this "dead" monitor back into the VGA port. Start computer. Start-up works fine, start-up messages and everything else displays fine on new HDMI monitor.

BIOS Version/Date American Megatrends Inc. P11-A3, 12/27/2013

I suspect I need to set something in the BIOS or update the BIOS, but I don't know how or what. Can someone help? I would prefer not to have a "dead" monitor under my desk connected to my computer.

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billsey

That's a weird one. Could you show us a picture of where you are plugging into the back? There were a bunch of different TC-605 models and they were different sometimes.

mikemickel

The picture of the back panel is attached. Top white wire is plugged into HDMI port and goes to new HDMI monitor. Blue-head is VGA connection to old unplugged monitor. Would it be safe to unplug the old monitor while Windows is up and running and would it maybe tell us anything useful? Any chance that would allow the boot messages to successfully display on the new monitor after next restart? I'm grasping at straws here. I am, of course, open to a more fact-based procedure. Thanks for your help.

20200610 Acer Back Panel.JPG

billsey

Yeah, you look like you're doing it right. At least I can't see a GPU card installed. Sometimes when we have people with this type of issue it's because they have one monitor on the GPU and one on the motherboard. It would be safe to unplug the VGA while the system is running and that might give us some indication as to what's happening.

mikemickel

I unplugged the VGA cable from the computer while Windows 10 was up. As I kind of expected, there was a chime (presumably saying something disconnected) and then everything continued normally. The display on the HDMI monitor continued with no interruption. Then I selected "Update and restart" from the power menu (a Windows update was apparently scheduled). System shut down; I heard one beep; an "HDMI" message with a couple extra lines appeared briefly in the upper left corner of the monitor; then the screen went blank. I powered off and powered on and got a repeat of same scenario. I powered off, connected the VGA monitor (still with no power cord) back into computer, powered on, got normal restart: Acer message, "Hit DEL to enter Setup" message, etc., and on to Windows 10 sign in screen. As I type this message I am viewing it on the new HDMI monitor---but with the old monitor physically connected to the VGA port.

billsey

That is about as weird as it gets... What happens when you try with the VGA cable plugged in, but with no monitor attached?

mikemickel

I get same bad result with the VGA cable plugged into the computer and not plugged into anything at the other end. I assume this has something to do with the BIOS, but I have no idea why it will write to the new HDMI monitor when the old one is plugged in but won't write to it without the old monitor connected. As I mentioned, something gets sent to the new monitor even in the "bad" case, because the "HDMI" message briefly appears before the screen goes completely blank.

mikemickel

Anyone have any ideas that would allow me to unplug my VGA monitor?

billsey

The only thing I can think of is to pick up a separate GPU card and put it in the X16 slot. There's something weird going on with your MB and swapping the graphics to a card would disable the onboard video.

mikemickel

Okay. Thanks. Since we don't use any advanced graphics, I think I'll just leave the old monitor plugged in in a corner under my desk for now. Maybe we will try a new GPU card at some time in the future. I had hoped there might be some BIOS setting that would get around this problem, but I guess not. Anyhow, thanks again for all your input.