Small cheap monitors, one works, one doesnt ?

Hello , hope you can help/suggest etc (or just learn from this)

I've developed a project using Arduino 1.6.6 the TVout library that works fine on larger TV screens and on a 7" car monitor on my bench, but when I came to plug into the 3.5" screen it must actually work with I get vertical ghosting, flickering and a black line near the bottom of the screen.
No problems horizontally.
The reverse camera kicks in at the on-demand channel as it should, and runs perfectly.
I made code changes for NTSC and PAL, it made no difference.
I've even had the 7" and 3.5" running off the same output (Uno R3?) , simultaneously ... the big one works, little one flickers and ghosts.
With 'Pert' 's help I've updated my TVout files with the 4-month old TVout fix for modern LCD's on Github by Avamander? but still the same.

Stripping the screens down, I see the larger one uses the MST702 chip. That works fine.
The smaller screen runs a AMT630 chip, allegedly a clone of the MST703. This must be the root of the problem ?

Anyone have any coding solutions to try? Changes to TVout etc?

Am I missing something obvious?

Prefer a software solution if possible, as the screen still has to work with a camera on its other input.

I'm not a stranger to code, but I don't fancy analysing and cut/pasting the relevant code from TVout, TVfonts and Video_gen etc etc unless its definitely going to help me. (I believe Libraries slow it up but is that really the issue with this other chip?)

Maybe this is an old thread and I'm not searching with the right keywords (all the fluff on touch screens LCDs etc gets in the way) if so, please point me in the right direction and accept my apologies.

David.

Sadly no help from anyone yet.
After reading that an impedance mismatch causes ghosting I've tested the inputs on the screen... an almost perfect 74 ohms. So its not that.
Grounding some of the signal through small value capacitors in parallel was no use, with no effect (smallest values) or blurring the characters on screen (with 10nF)... blurred ghosts! great! so its not that.

One thing I did notice was that the blue onboard chip-generated graphics ("AV2" in the corner to signify which channel is in use) are perfectly clear with the camera signal or no signal, but with the arduino signal the blue characters are distorting and ghosting .. so whatever is causing the flicker and ghosting is affecting the whole screen output.
Not sure how that helps me.

I will try some code changes, in case Its anything to do with the standard ( 128x96?) line count etc, but with the very simple code below still presenting the ghosting and flickering I'm getting nowhere with this.

Q... has anyone been able to get a simple 4.3 or 3.5 inch screen to run TVout without issues? Do I buy a new screen??

the code...

#include <font4x6.h>
#include <font6x8.h>
#include <font8x8.h>
#include <font8x8ext.h>
#include <fontALL.h>
#include <TVout.h>
#include <video_gen.h>
TVout TV;

void setup() {
// setup code, to run once:
TV.begin(PAL); // sets default 128 x 96? sized screen
// TV.begin(NTSC); // remmed out in this instance, make no difference if used.
TV.select_font(font6x8); // sets character font on screen
} // end of setup loop

void loop() {
// test signal only, producing the flicker and ghost on some, not all screens?
TV.print(0, 2, "Engine ");
} // end of main loop