comp.sys.sinclair FAQ


In addition to the information provided here, several technical and service manuals are available that may be of interest to you. These cover the operation and configuration of these components in considerably more detail than is possible here. Please refer to the documentation page for links to these resources.


AY-3-8912 Sound Chip:

Keyboard Layout:

128K Composite Video Output:
Pin 1 is composite PAL, 2 is GND. There's no audio on any pin of the RGB connector.

The picture is a bit dull unless your TV's video input is High Z (high impedance) However, that's quite unlikely. Normally the impedance of the video input is around 75 Ohms. To alleviate this problem, short the 68 Ohms resistor inside the Speccy that's in series with pin 1 (follow the track on the PCB). Or you can hook it directly to the input of the RF modulator.

The audio can be taken from the MIC socket but a better balance between 48K and 128K sound is obtained directly from pin 5 of IC38.

128K RGB Video:

Power Supplies:
Information about hardware and peripherals with entries elsewhere in this FAQ can be found on the appropriate pages.

ZX Interface I RS-232: The RS-232 socket provided on the ZX Interface I has the following configuration:

  1. Not Connected.
  2. TX Data - Input.
  3. RX Data - Output.
  4. DTR - Input. This should be high when ready.
  5. CTS - Output. This should be high when ready.
  6. Not Connected.
  7. Ground. Pull down.
  8. Not Connected.
  9. +9v - Pull up.
\ 5 o   o   o   o   o 1/
 \  9 o   o   o   o 6 /
An RS-232 cable will be required to connect to other peripherals. This must be wired as follows: » Further ZX Interface I details