Brand: Sinclair Research Ltd.
Model: ZX Spectrum
Country of origin: Chile
Made in: United Kingdom
First year of production: 1982
Board design: Richard Altwasser
Software: Steve Vickers (at Nine Tiles Ltd.)
Case design: Rick Dickinson
Dimensions: 233 × 144 × 30 mm (feet adds 2 mm)
Weight: 579 g (Issue 4B)
A factory modified ZX Spectrum to run on NTSC TV’s.
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This NTSC version was only sold in Chile and Peru where the NTSC TV system was used (channel 2 or 3 selectable). Apparently it was to be sold in the USA, but it failed the FCC certification, even though several precautions were applied to suppress emitting stray RF signals such as the use of two DC coils and a metallized case, all of which was not mandatory in Chile. It also has a provision for a channel switch for a NTSC RF modulator, as found on many US homecomputer of the time.
All Issue 4/4B motherboards have soldering pads for the attachment of metal prongs, although not many boards were modified for NTSC use. A special ULA with different timings was produced: the Ferranti 6C011E-3. The Master clock crystal is 14.110 MHz, this produces 264 lines per frame (PAL: 312 lines) with a scan line time of 63.5 µs instead of 64 µs for PAL. The frame rate is 59.6506 Hz instead of the usual 50 Hz. The CPU is clocked at 3.5275 MHz (14.11/4).
NTSC ZX Spectrums were unknown outside of Chile until it was first spotted in 2014 and not many have surfaced since.