From the factory, the Spectrum +2 has several issues with the video output that are well documented in this Byte Delight PDF. The first involves moving one of the leads of capacitor C31 to inject the audio directly into the modulator, via TR11, rather than the TEA2000 chip. On both of my +2’s this capacitor is installed on the back of the PCB. This was a simple case of desoldering one of the capacitor legs and adding a small extension to connect to transistor TR11.
The second fix is a little more bizarre. Apparently, Sinclair installed three of the transistors backward? The document explains that they must have swapped the model to one with a different pin-out. It also is reversed when compared to the PCB silkscreen. Only one of the transistors, TR4, actually needs to be reversed to fix the composite video output. Note that it will be reversed to the silkscreen when you have fixed it!
I tested the composite output after each of the fixes and both made significant improvements. With both of them implemented the output is crystal clear. So I recommend making these changes if you have a Spectrum +2 (Grey).
The final job was a full recap. I know this is controversial, but having tested lots of capacitors removed from 1980’s Spectrums it’s very hit and miss as to whether they are anywhere near their original specification.
With both fixes installed I tested using my diagnostics boards with no issues and a lovely clear picture. I had to test with a few games (Paperboy, Knight Lore, and The Hobbit).