Sinclair ZX Spectrum Service Manual
Spectrum For Everyone https://spectrumforeveryone.com/
57
10.3 ASSEMBLY OF THE KEYBOARD FOR THE SPECTRUM+
The flextails running from the keyboard to the clamps should lie in an S shape, to prevent tension in the
membrane. This is achieved by ensuring that the end of the tracks on the middle layer protrude by 1mm
past the clamps. This is easily seen on the wider tail, but not so clear on the narrow one. Visible markers
are provided on future membranes.
When clamping the flextails, ensure that an extra packing piece is included under the tails at the clamp
position. (These are fitted to current production models). These should be approximately 0.75mm thick,
and as wide as the tail. Paxolin is a suitable material. This section does not apply to any Spectrum+ which
has S as the first digit in the serial number.
When assembling the keyboard, it is advisable to tighten the screws in the following order:
• Centre line of 3 screws first
• Screws adjacent to tail clamps last
The screws should be tightened to the minimum to give a firm fit, (e.g. a quarter-turn back from full
tightness).
Ensure that on each membrane tail the 2 tail surfaces are stuck together, to avoid short circuits on the
board. This is best achieved by using a piece of double-sided tape, or a pair of tabs around the edges, near
the connector end. This is current practice in production.
Both metal and plastic reaction plates are possible. The metal plate has to be accompanied by a plastic
insulator. The plastic reaction plate is similar and cheaper. The metal plate needs 6.5mm fixing screws and
the plastic plate needs 8mm.
It is advisable to check the operation of all the keys on newly assembled keyboards.
10.4 KEYBOARD OPERATION
The Spectrum+ keyboard is in effect two switching membranes in parallel, a 'top' membrane and a 'lower'
membrane.
The top membrane is similar to that for the Spectrum 48k, except that pressing any one of the following
keys also makes contact between row 1 and column 6 on the top membrane in addition to their dedicated
row/column positions:
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