Not having a Dig here everyone, as I am Glad people Post these Comments so other Users do Not Make Mistakes.
I was Very Cautious in my "dangerous experiment", doing the exact Same MOD as this fellow... Michel, and even achieving His Very Same Results! "this worked, the video was very dark and I had to increase the brightness and contrast to almost maximum levels"
I have since Discovered the Minor Differences between the ZX Spectrum and the ZX81 RF Video Outputs, amazing what you can find on GOOGLE these Days, and am now aware of the required Transistor and Resistor in the Circuit.
I have a Spare Working TS 1000 ISS 3 Mainboard, that is Floating about my Computer room, so I will attempt the Transistor and Resistor Composite MOD on this Unit First, before Hacking into my Nice Like New TS 1000!
Darren in OZ
zx81user wrote: ↑Fri Apr 26, 2013 3:28 amI received another TS1000 but I couldn't get my TV card to tune in to the modulator RF channel. So I thought I would take the board out of the modulator and feed the video signal directly into the TV. Although this worked, the video was very dark and I had to increase the brightness and contrast to almost maximum levels. By analyzing the video signal I saw that the back porch was there but the sync level was way below normal CVBS levels. I thought that I could probably rectify that with a few series diodes, so I took some ordinary 1N4148 diodes, soldered them in series and voila, a beautiful crisp picture! It's a very simple mod that works well for a 210 ULA with back porch but not for ULA that hasn't got this back porch. The diodes also protect the ULA from ESD, so it's a quick simple mod.