Nintendo zappers are supposedly much more reliable than the SMS phaser usually. The odds of finding 3 non working ones is very low, tho not impossible those days with people trying to sell anything labelled Nintendo.
As other people I'd suggest you to fiddle with your contrasts and luminosity settings - if you have an old camera, a PSP or something able to display pictures on your TV, use test pattern cards. They aren't only to tune your TV on a channel, in ye olde days of analog broadcasting, they were also for settign your TV luminosity - and you need to do so - with the upcoming of digital TV at the end of CRT life, and the lack of fidelity of early LCD TV, the usual settings were tuned to low contrast and high color saturation, for more "vivid colors" but an overall lack of depth for the picture, as the human eye is much more sensitive to contrast than colors (it's one reason why black and white movies always seems more contrasted and "deep" that color movies).
More adapted to NTSC TV sets obviously
More for PAL sets, but you can use it; I fidn the black and white scale easier to use.
And you can always check your color settings as well :
NTSC test card (it is important, as NTSC have hue variation than PAL doesn't have - tho it's mostly on early, all analogue TV)
And if you have a 16/9 set :
PAL version... reversely, because PAL suffer from chroma variation (in early sets only or some cheap Chinese stuff)
You can notice that those cards also allow you to check the geometry of your tube, and the amount of overscan (that is, the amount of picture you do'nt see because it's over the physical display).
If your TV set is a flat screen, overscan should be minimal, but there might be some, most probably on the right and left parts if it's a 4/3 display (to reduce the black bars of 16/9 emissions) or up and down (to allow a larger display of 4/3 broadcast on a 16/9 set).
Your TV might or might not allow you to access to such advanced settings. But we're going a bit too far for just contrast settings here
Edited by CatPix, Sat Sep 26, 2015 1:14 PM.