The Nebula is a Spectrum 48 daughterboard, designed to replace the ULA chip found in UK Spectrum motherboards (versions 2 to 6).
The module’s video output is the same as that provided by the original ULA (IE: YUV to drive the Spectrum’s modulator circuit. Naturally the best picture is obtained when the Spectrum has been composite modded but RF still works). When fitting to issue 2 boards, VR1 and VR2 need to be
adjusted to correct the colour offsets – as would have to be done when replacing a normal ULA.
On rubber key Spectrums, space between the ULA socket and top cover is extremely limited. If some of the nearby logic chips (IC3, IC4, IC24, IC25) are in sockets they may cause tension in the case when re-assembling. It’s is strongly advised that these chips are soldered directly to the spectrum PCB.