Spectrum Issue 1 & 2 Tuning & Colour Adjustment
Early versions of the 16K and 48K Sinclair Spectrums suffered from yellow tinges to the screen and were famous for "wandering off" channel.
The procedure below describes how to adjust this on Issue 1 and Issue 2 versions of the Spectrum.
Tuning & Colour
On Issue 1 & 2 boards, the colour synch and colour balance can be adjusted to help with tuning difficulties. Yellows which should be white, dot crawl and difficulties getting the colour to “lock” are very common. On some TV’s it is impossible to even achieve colour. There are two preset capacitors and two variable resistors all in a row (see diagram below).
Adjustments must be made with the power on so you can see the effects of your tweaking on the screen. Use a very small screwdriver and take care – only a very small movement is needed.
The short program below will help to monitor your results by displaying a series of coloured bars:
10 FOR N= 0 TO 7
20 FOR M = 1 TO 3
30 PAPER N : PRINT “ “
40 NEXT M
50 NEXT N
60 GOTO 10
The clock trimmer is used to minimise dot crawl.
The colour synch trimmer should only be tweaked if you have no colour at all.
The colour balance controls should be tweaked together to give good colours and a nice neutral white. This is trial and error stuff, so be patient !
Issue 3 boards & onwards have improved ULA circuitry which is self adjusting so these pre-sets are not fitted. Production was switched to Taiwan from this model onwards.