NEO supergun to TV problem

I have a neo supergun (self made) that works perfectly on every tv except one. Every other console with RGB output works perfectly on this TV though, so it's probably not the RGB input on the TV that's causing the problem. The supergun works perfectly on every other tv so that shouldn't be the problem as well. What happens exactly is that horizontal lines made up of small 'blocks' flash on screen at short intervals and anywhere on screen (see picture, it's not too clear though). sometimes the number 'S100' is recognisable.

I hope anyone can help me out on what may cause this. It has the feel of a loose solder joint or contact, but since it works fine on any other TV this probably isn't the case...

oops Sorry

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