LG 49UJ630V on/off/on/off/on/off

I spotted it doing this a few times after initial switch on, it would sometimes do a reboot, but I put it down to it updating its firmware. Whether it was or not, I am not sure, but, yesterday, whilst watching it, it switched off and back on - I assumed I might have just caught one of the remotes. It is an LG 49UJ630V 49" LED model, which I bought new around 18 months ago.

Today, after turning it off, began on/off, on/off in a cycle of a few seconds, not long enough to even fully boot up. Turning it on, the on/off, on/off performance continued. A bit of internet research suggested it seemed to be a common problem, but none of the suggested fixes (give it a thump, by the PSU /plug area) helped at all, I didn't really expect it would, so time to remove the back for a proper look inside.

Everything looked perfectly clean, nothing obvious at all, no swelled, burst, or leaking capacitors, so I went round it re-seating some of the likely plugs and ribbon cables, then checked the PCB fixing screws were tight onto the steel chassis. Four of screws, two per PCB were loose, so I tightened those and powered it back up, laid flat on the carpetted living room floor for a soak test. It is behaving perfectly, stays off when turned off, stays on when turned on. Time to reassemble it I think..

[EDIT] Well it behaved itself absolutely perfectly laid face down on the floor, after I had re-seated everything, I spent a good hour soak testing it whilst on the floor, just the power lead connected. Turned it off - it stayed off, turned it on it stayed on.

I then put is all back together, re-installed it, ran a brief test with the terrestrial antenna connected, watching a live channel, all good so I reconnected the HDD, Sat, Fire Box and etc. more testing and it began the on/off, on/off again. Everything except power removed and the on/off continued.

I then thought to see if there was anything in the menu, like an update to try. I couldn't find that, so instead tried turning on the General> Quick Start+ option. I have this normally set to off, since setting it to on, there have been no further misbehavior at all.

[EDIT 2] After an hour with no problems, I went back into General> Quick Start+ and turned it off, it has run fine since then, but........

[EDIT 3] ..and still working fine, which is rather weird. I wonder if rather than electronic issue, it might have been an issue in the configuration - my simply changing the config, rewrote and refreshed the file ????
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..and still working fine, 24 hours later. When I first had the problem and unable to find a fix, I emailed LG's UK tech department explaining the problem. They are supposed to get back to me within five days, I should hopefully be able to add to their knowledge with my own fix.

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