Extended Desktop issue when unplug USB printer!

[sre]

I have a very weird adverse effect to report and ask for any solution available:

I have a MacBook (unibody edition) with a Brother USB laser printer connected, and I have purchased a VGA adaptor in order to connect my external VGA LCD NEC monitor. All is fine, using my external monitor in extended desktop mode, until I unplug the USB printer: then the computer no longer sees any external monitor connected anymore! This happens even when the printer is switched off!

Can anyone help, please?

 

[johnnyham]

Have you tried plugging in the VGA adapter without plugging in the printer? What about other USB devices? Does it do the same with the other USB port?

It sounds to me like your VGA adapter only works when the printer is plugged in - since the VGA adapter stops working once you unplug it, I think it's a physical issue, where one of the ports is shorting out the other. When the printer is plugged in, it corrects this, but when it's unplugged, the short returns. If that makes sense.

 

[sre]

It only relates to the printer, irrespective of the USB port that is plugged in. Only if the printer is plugged in the computer can see the extended monitor...

I don't know if it's the VGA adaptor or -god forbid- the external monitor port on my Macbook.

 

[johnnyham]

Ok, let's assume that it's not a physical problem. Did your printer come with any software that you had to install? If so, there could be some weird conflict going on.

While we're at it, if you can get your hands on another Macbook, you could rule out the VGA adapter as the culprit. Also, out of curiosity, is the VGA adapter an official Apple one or third-party?

 

[sre]

I think I installed a driver and I do suspect a s/w driver conflict. The adapter is third-party (China-cheap but standard). I'll test the adapter as soon as I get another macbook handy, of course.

 

[sre]

Additional info - scanner or printer!

I'd like to add here that I just discovered that this problem occurs with my HP scanner/printer as well: that is, if I disconnect the Brother printer and connect the HP scanner/printer then the Mac can see the external monitor! It does not when the printer is unplugged from the mains.

Overall, it seems that for the mini display to VGA adaptor to operate it needs a printer connected to the MacBook's USB port AND the printer connected to the mains. I ran the extended Apple Hardware Test and the MacBook passed it. So, is it an adaptor issue?