29-08-2013, 12:53 PM
Technically this article borders with Vintage Computing, but the mod described here applies to all devices where a UHF modulator block is fitted as standard but composite is desired.
The problem with a lot of the older equipment is that it is designed to work on a standard analogue television, be it an old computer, video player, pong game or whatever. Generally the signal offered up to a modulator block is already composite in nature and its a case of just extracting the signal. There in lies the rub, do you mangle the case of an original device to fit a composite socket or is there an easier way.
For this mod, all I required was a 100uf 10v elect capacitor and a three way config jumper along with config pin that you find in computers. Pop the lid off the modulator box and with a fine soldering iron lift the wire leading to the RCA socket centre connection. Outside the can, fit the 100uf cap, negative to the composite signal supply, feed the positive wire through the spare hole into the modulator block. Looking at the three possible connections on the config jumper, wire the centre connection to the RCA centre connection, wire the disconnected modulator feed to one of the out pins and the positive capacitor wire to the other. It is advisable to insulate the capacitor lead with a piece of heat shrink sleeve. Finally, fit the config pin in the required position and test.
Advantages of this method, you don't ruin the originality of the device as has been done by some authors in the past by removing the modulator can. The unit can be converted back to UHF operation by movement of the config pin. You don't need to fit an additional RCA connector at the rear and ruin the device, important if it is a really rare computer such as a ZX80 or a Jupiter Ace with the brittle vacuum moulded plastic cases. Finally, the quality of the signal being provided in composite is superior in quality to that of the UHF feed and with the diminishing availability of analogue television sets around this mod will ensure that the older computers will be usable for years to come.
The problem with a lot of the older equipment is that it is designed to work on a standard analogue television, be it an old computer, video player, pong game or whatever. Generally the signal offered up to a modulator block is already composite in nature and its a case of just extracting the signal. There in lies the rub, do you mangle the case of an original device to fit a composite socket or is there an easier way.
For this mod, all I required was a 100uf 10v elect capacitor and a three way config jumper along with config pin that you find in computers. Pop the lid off the modulator box and with a fine soldering iron lift the wire leading to the RCA socket centre connection. Outside the can, fit the 100uf cap, negative to the composite signal supply, feed the positive wire through the spare hole into the modulator block. Looking at the three possible connections on the config jumper, wire the centre connection to the RCA centre connection, wire the disconnected modulator feed to one of the out pins and the positive capacitor wire to the other. It is advisable to insulate the capacitor lead with a piece of heat shrink sleeve. Finally, fit the config pin in the required position and test.
Advantages of this method, you don't ruin the originality of the device as has been done by some authors in the past by removing the modulator can. The unit can be converted back to UHF operation by movement of the config pin. You don't need to fit an additional RCA connector at the rear and ruin the device, important if it is a really rare computer such as a ZX80 or a Jupiter Ace with the brittle vacuum moulded plastic cases. Finally, the quality of the signal being provided in composite is superior in quality to that of the UHF feed and with the diminishing availability of analogue television sets around this mod will ensure that the older computers will be usable for years to come.
