Wiring of a SPECTRA compatible SCART cable
Video signal absent indicator
The SPECTRA interface uses the luminance (/Y) signal present on the Spectrum’s
expansion bus to synchronise the display it outputs from the SCART socket with the
standard TV picture generated by the Spectrum. This signal is available by default on
the majority of Spectrums, except for issue 1 and early issue 2 machines. In these
issue machines, it is taken to the expansion bus via a short wire link but this link is not
always fitted. On later builds of the issue 2 Spectrum the link was fitted as standard,
and in subsequent issue PCBs the link was removed altogether and replaced with a
continuous track. The purpose of the video signal absent indicator LED on the
SPECTRA interface is to provide a visual indication should the luminance signal not be
found. Note that upon powering up the Spectrum, the LED will light but should then
switch off almost immediately. If it stays on then it is highly probable that the Spectrum
does not have the link fitted and so one must be soldered in.
It is possible to identify an issue 1 or issue 2 Spectrum from a quick visual inspection
through the rear expansion port. If a heatsink cannot be seen spanning across the top
of the expansion bus then the Spectrum is an issue 1 or issue 2 machine. If there is a
daughter board spanning across the expansion bus, then the Spectrum is an issue 1
(the daughter board was used to expand the computer from 16K to 48K, whereas in
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