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The +3 (as well as the +2A) has RGB video output. Although this output type provides the best quality for video display, not all TV sets have RGB input. Even if a SCART connector is present, the RGB input on the TV side may simply not be implemented.
All 128K Spectrum versions (+128/+2/+2A/+3) are using the same PAL encoder circuit, TEA2000 , which drives the TV modulator. On the +128 and +2, the PAL encoder drives also a composite video output circuit. On the +3 and +2A, the composite video output circuit is missing.
This composite video output diagram shows the original +128/+2 composite video output circuit, which can be successfully used on any +3 (and +2A).
However, the same diagram includes a better alternative for the video output, based on the TEA2014A , a circuit commonly used in many TV sets for internal TV / external VCR switching.
Note: on this drawing, the TEA2014A may well be replaced with TEA2114 . In fact, TEA2114 has better electrical performance, but it may be also more expensive. For the purpose of this application, there is no particular reason for using it.
On the original +128/+2, the composite video output is connected via pin1 of the RGB PERITEL connector. Although this solution may also be applied to +3 (and +2A), I don’t recommend it. The common standard for video connections are the BNC connectors (used mostly in professional video equipments), or RCA connectors (used mostly in consumer video equipments). This example shows the video BNC connector mounted on the rear of my original +3, while a view of the solder part of the same BNC connector can be seen in this other example .