My samsung LE40R74BD set works fine for about 10 mins then screen goes blank (black) . It would appear there is no back lighting. I have visually checked the psu for blown capacitors but all seem to be fine. Any suggestions ?

Just do a hard reset to this set and check. Unplug the TV from AC mains wall socket, and re-plug it back after 10 minutes or so. This must make it a hard reset.

Check to see if the screen saver went on, and it's a blank one, or if the sleep or hibernation mode is set for 10 minutes, or so.

Bad capacitors in power supply.

Have you check screen power down could be it is setup to shut down as you say after 10 mins. Access power through control panel, change settings ie to 30 mins
Fingers Crossed>?

sounds like the backlight is out, can you see a picture when shining a flashlight on the screen. if yes you have either a bad inverter power supply or bad screen (panel).
both are serious , also could be just a few bad capacitors on the power supply, if you want you can do a visual of the power board caps will appear swolled on top and are easy to solder in cost about $1 EACH

I’m happy to help further over the phone at https://www.6ya.com/expert/eric_ab7c09ec01841771

Its simple bro , Your CPU is not reading RAM,so just Remove and Re Insert the Ram to in DIMM Slot and then Switch on Computer it will work fine.

Yes your inverter is bad, I have the same problem my set is about 1 and 1/4 years old. Because Olevia makes a terrible product there inverters are attached directly on to the panel, which means they will only sell the inverter along with the panel i.e $700+ to replace + $100 dollars labor if u don't know how to fix it ur self. I am currently searching to find the manufacture that makes the inverters because olevia will not disclose that information. I believe it is darfon, if so the inverter should cost about $150-200 depending. If you dont believe you can fix it ur self ur best bet is try and sell the set for scrap take ur $100 or so dollar and buy a quality product! Oh and dont call there support they will tell 10 different things before u find out this long for seen truth!

Well since you seem to have tried a bunch of thing why nor go a bit more and replace your video card. Below is a link to your PC:
http://support.packardbell.com/uk/item/index.php?pn=P280110001&g=1400

I fixed it. Went back in after a twenty min. break, figured if it's broke I can't break it again, might as well try to fix it(out of warranty, so much time on 1st. bulb, after fixing I found out had 8463 hrs. on 1st. lamp! WOWW most i've seen on any strings out there,and I'm really cheap and inquisitive) But this is how I did it. pulled off covers. looked around pulled light box out checked connectors and resistors visually for burns, none found, then I see a clear plastic sleeve covered group of wires it was plugged up at the ballast where i was working earlier but not the other end, so i looked around for the plug to insert it, couldn't see any where. I felt on top of a silver polished panel w/holes allover, there on top, at the right side of the silver panel was a plug for it. I plugged it in by removing fan and cooling fin assembly, for room to work(and good chance to clean dust from the fins and fans. I tilted silver panel down to see the top, after some removing spring loaded screws holding cooling fins, (the screws ave very light spring tension and won't pop out, I swear, keep track of springs for reassembly later) plugged it in(only goes one way, don't force it, flip over if it doesn't fit nicely) replace all removed parts in reverse order and reinstall covers, plug up, and mine powered on almost instantly. After that and spending 2 hrs. online trying to go through all the strings everywhere about these problems. It came down to trial by fire. I hope this helps, reply if it doesn't.