Cheap RGB Monitor

by Roger Dowling

An RGB monitor on the cheap – providing that you already have a Ferguson TX9 or TX10 colour set!

The Ferguson TX range of televisions privide an easy conversion for RGB use and work very well with the Nascom AVC. The AVC gives an RGB output as standard rather than PAL encoded video and so an ordinary composite video input colour monitor is of no real use without adding an extra encoder board to the AVC which apart from adding to the cost of the board, it will also reduce definition. All the Ferguson TX models except the very early TX9 can be converted as data insertion points have been provided on-board to enable some models to be equipped with teletext reception without fuss. The TX10 has been the standard large screen (22 and 26 inch) chassis for a couple of years and the TX9 has been the very popular chassis used in models from 14 inch upwards.

If you are the possessor of a Ferguson TX set (I believe that a1l models have TX somewhere on the front or possibly back cover) then you check to see if you have a TX9 or TX10 simply by looking in the back. If there is only one horizontal panel then you have a TX9. The TX10 has two panels, one large horizontal one and a vertical panel at the extreme back of the set which will hinge down to a horizontal position.

To check whether you have an early or late version of the TX9, you must identify the PAL decoder IC which is a 28 pin device and will be found near the middle of the panel. If it is A TDA3560 or TDA3561 then you are in luck. The earlier type is marked PC1365.

The data insertion points on the decoder IC are on pins 15 (R), 15 (G), 17 (B) and a switching input on pin 9. These pins are conveniently wired to a 6 pin plug on the board PL18 although for some obscure reason the plug connections are slightly different between the two types of chassis. I will give details for the TX9 and show differences for the TX10 where they occur.

The RGB outputs from the AVC are at a level of 1 volt and are therefore suitable to feed into the data insertion points via isolating capacitors. Leading these outputs with 75R provides the correct contrast level displayed on the CRT. A synchronising signal also needs to be fed to the receiver and can be obtained from TP8 on the Nascom AVC. The i.f. module should be removed from the set. This is a plug-in module consisting of two integrated circuits, one of 16 pins (TDA2540) and one of 8 pins (SL430). It should be easy enough to identify – on the TX9 it is on the far left (looking in from the back)