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.

On Issue 1 & 2 boards, the colour synch and colour balance can be adjusted to help with colour accuracy and 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 on the main board.

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 you 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

Run the program, then make the adjustments:

  • 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 take your time and 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.

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