The LM1889N is the TV Video Modulator chip (NOT to be confused with the large metal TV modulator) which translates video signals from the Spectrum ULA into a television-friendly format.
If your Spectrum suffers from strange colours, this may be the chip to replace. If your Spectrum is an Issue 1 or Issue 2 Spectrum, you should change the dials to "tune in" the colour correctly, but if this proves impossible it may be a new LM1889N you need.