TommyCooper

Have you made the teachers aware of how much replacement pens cost, and that every time you have to buy replacements it's money that can't be spent on other teaching resources? Sounds like your teachers need some additional education!

Have you tried another computer to see if that show the same fault? If it still drops the connection after 5 to 10 mins I'd suggest getting hold of the serial number and contacting Steljes (the warranty holder for most 4065s sold in the UK). They might have some other suggestions for you to try but they can probably also help if it's still under warranty and has a fault.

The PSU is a 5 volt, 2 amp supply with a centre-positive connection to the board. Any replacement PSU that has the right connector and meets those specs should be suitable.

Did you get this fixed? I'd suspect the affected laptops had USB 3 ports, and should normally be fixable by connecting the boards via a USB 2 active extender.

I agree on the cabling being the likely issue here. If you're using VGA cables make sure they're fully populated and properly shielded too.

Can you set the projector to be the primary display? In duplicate display scenarios Windows will default to the resolution of whichever display is set to be primary.

Try this: https://www.epson.co.uk/gb/en/viewcon/corporatesite/products/mainunits/faq/3812/2867

Have you installed Intel's proprietry drivers? Their control panel should have options to adjust the display scaling to hopefully eliminate the letterboxing.

It'd be unusual but not unheard of to have the same fault on multiple displays. Does the flickering issue happen if a different make or model of laptop is connected? I'd want to confirm that it isn't a fault with Dell E5540 before going any further as the manufacturer will probably want to check that before authorising any warranty work. If the issue is still there with a different laptop I'd get hold of all the serial numbers and contact Steljes about it (they're the warranty holder for most SMART E70s in the UK). They'll probably ask you to check a few things first but if they're under warranty I wouldn't be surprised if they suggested swapping one of them under warranty to see if it improves things for you.

I don't blame you for writing off the mirror replacement! If my memory's correct the projector's as good as built around the internal metal bracket that the mirror's glued to.

UF70's can overheat causing premature lamp failure if they're fitted too close to the ceiling. There should be a 10 3/8" - 26.4cm air gap between the projector and the ceiling. If they're fitted too close go back to your installer and ask them if they read the installation template before fitting the projectors (copy available from http://downloads01.smarttech.com/media/sitecore/en/support/product/smartboards-fpd/800i6series/textless/mountingtemplatesb800i6sb600i6v07may2013.pdf).

4065's can be picky about the total length of the USB cable (including anything that's fitted in dado trunking). Try a shorter cable directly between PC and the panel, and make sure it's connected to a USB 2 port not a USB 3 one.

Have you tried using a separate VGA cable running directly between the PC and projector? When using VGA projectors have to "lock-on" to signal timing information that's sent to it along the VGA cable by the PC to show the correct resolution on screen. If the cable you're using is slightly damaged then picture data may be getting through properly but the timing information might not be. You could also try doing a factory reset on the projector. You'll need to go into the service menu to do this, and make sure you know how to change the projector installation orientation before starting as it might flip the image upside down at the same time.

Just found this thread - did you manage to swap the mirror assembly earlier this year? UF75's are fairly time consuming to repair so I suspect a large part of the cost you were quoted by TSC was the labour cost. SMART's newer UF70w will fit on the same wall fixings as the UF75w but I don't think you'll be able to buy them without getting another board too! A good alternative which will normally fit in almost the same place on the wall (you'd need to take a couple of measurements to check clearances) is Epson's EB-575W, but a de-install and re-install is needed as the fixing points aren't the same.

If everything's gone greyscale with no input it probably isn't the DMD chip. It could be a completely failed and stuck colour wheel, but more likely is that it's a failure on the main driver board. Both are technically repairable but might be costly if the unit's out of warranty.