Composite color video out

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Composite color video out

The Enterprise computer series (64/128) has three possible "monitor" outputs available. An analogue RGB for colour monitors, a monochrome composite signal for Black and White monitors and finally an RF output via the built in UHF modulator suitable for use with many televisions via the aerial socket.

The UHF modulator built into the Enterprise has its drawbacks, the longer you use the television for displaying the UHF signal the more the signal deteriorates until you are forced to fine tune the TV, this is due to the built in RF modulator being "famous" for its stability (or lack thereof !!).

Nowadays there are many TVs containing (baseband) video input and there are many monitors which are able to receive video signal only. (Not to mention the VCRs.) The emitter follower in question makes it possible to connect the Enterprise to them. It can be built into the machine and the colour PAL video signal can be led out of the computer through an empty connector pin. The signal containing the colour information can be taken from the base of the transistor represented on the original circuit diagram "TR8 (2N3904)". The composite video signal present here is generated by the integrated circuits "U34 (LM1886)" and "U35 (LM1889)". The one-stage transistor amplifier to be built-in can be seen in picture 1.Composite-1.gif

Now we are going to review how to build in the emitter follower. This work is recommended only for those who are expert in electronic tinkering. Not having the suitable tools (for example to do the accurate soldering) many sources of failure can be built into the machine disassembling and reassembling it. First of all, remove all the plugs from the machine and the BASIC cartridge from the left side of the computer. Unscrew the 14 (kereszthornyú?) screws at the bottom. The keyboard can be removed by carefully tipping it over (?). Now the transparent folder of the funtion keys' label can be removed. Slip upwards the upper housing/casing (burkolat?) progressively (fokozatosan?), slowly, in more places (?). Lift it down carefully because the foil cable can break. Remove the foil from the two connectors on the motherboard.