RGB modded N64 - retroRGB amp confusion

[Zen]

Have and old Japanese RGB modded N64 that suffers from the dark picture issue. Finally decided to do something about it . . . myself (possibly my first mistake!)
It is the lifted leg version of the mod (it also has a wire running from the video chip, to a leg on the cpu? v-sync?).
Anyway, I fitted the retroRGB amp to brighten things up but I seem to have ended up in the RGB twilight zone. The screen is nice and bright and not much else. Game loads, a few garbled shapes and colours, then a white screen with a some flashes of colour.
I am using modded RGB scart cables, that probably have some form of internal amp. Could that be the problem? Seems each step I take, adds more variables for error.

Any of you N64 modders run into this issue? Help and advice appreciated.

[RGB0b]

Do you have more info on the original mod? Also, can you open the SCART cable and see what components are inside? There should just be some capacitors.

[Zen]

Sure. Original mod as follows: VDC chip has legs 17, 19, and 21 lifted and soldered to respective AV socket points. Leg 8, on the opposite side of the VDC chip, is also lifted and soldered to a lifted leg on the GPU chip.
One of my Scart cables has single (resistor or amp, not sure) added. The other Scart (which does not display the image in correct aspect ratio) has a one inch, black addition of some sort.

I desoldered the RGB wires from the AV socket, soldered them to their respective points on the retroRGB chip, fitted the chip and soldered the chip to green, blue, ground and 5v on the top row of the AV socket and red and ground on the bottom row.

[RGB0b]

Do you have just a regular SNES RGB cable to test with? Also, can you post pictures of the inside of your SCART head?

[Zen]

Images seem to be awkward to upload (need to already be on the web?), so no pics, sorry.
Went through a few boxes of cables looking for basic SNES AV cable (I seem to have as many boxes of cables, as I do boxes of consoles/controllers!). No luck, it refuses to be found.
I suspect my amateur soldering skills at this point but i'm fairly sure that all instructions were followed correctly.

[RGB0b]

My guess is it's the cable. I'd remove all the components (even the caps) just to test and see if that makes a difference. If it looks like it's working, then add the caps back to the R,G and B lines.

Also, you can upload the images to imgur and post the links.

[Zen]

I will give that a shot and report back if I have success. Frustrating to think that it could be a cable issue, after all the work.
Thank you for your suggestions and for taking the time to help.