INMC 80 News


October–December 1981, Issue 5

Page 19 of 71

N1 Graphics

ROM Graphics unit for Nascom 1 (a.k.a. Econographics)

a review by Rory O’Farrell.

This hard to find item was trapped for me by Bits & PCs, to whom much thanks. Other dealers were saying that the Econographics kit was unobtainable (even the INMC80 suggested this in the INMC80-2 newsletter). It costs 30.00 plus VAT, and consists of a P.C. board about 6″ x 3.5″ which is singlesided, and soldermasked. On this board are (or will be when you put it together) 3x24 pin DIL sockets, and sockets for 4 smaller i.c.s. You are also supplied with a short length of 24 way cable and two 24 pin DIL plugs. This umbilical is wired up to connect from one socket on the Econographics unit to the socket on the N1 which held the character generator.

The instructions for assembly are fairly clear, but suppose that you have already assembled an N1 so that you know about the handling of MOS character generators. You first solder the 37 (THIRTY SEVEN !!!) links on the board, the capacitors, and the sockets. Soldering the capacitors is where the trouble starts. The instructions say that you should line up the + mark on the two Tantalum caps with the + mark silkscreened on the board. There is no such mark! Then when tracing the tracks to find out the polarity, so you can insert the tants properly (Tants don’t like reverse voltages – normal rating is less than or equal to 0.3 volt in reverse), while tracing the tracks to find the polarity, you notice that pin 1 of the input socket, which carries −3v is connected to pin 16 or 14 of the small i.c.s. Worried by this, you then check a bit further, and find that pin 2 of the input socket is connected to pin 3 of IC1, which expects + 12 volts. Now panicking, you go away and have a cup of coffee. On your return, you inspect the board. Definitely, the tracks are mixed up somewhat. You also notice that IC4 does not appear to have any connection to pin 16. However, the problems are easily solved.

Holding the board, looking at the track side, with the 24 pin sockets towards you, IC4 is at top left. Pin 16 is the top righthand pin. It needs to be connected to the broad horizontal track just about it. The track should have the solder mask scraped off it with an XACTO knife or similar. The input socket is the bottom right of the board, and pins 1,2,3 are the rightmost on the bottom row. With a vero cutter, or a hand held drill bit, or the knife, cut the connection to pad 1 and 2 from the direction of the top edge of the board. This will leave connections to those pads coming from the direction of the bottom edge of the board. These are correct. Using an insulated wire link, link pad 2 (the second one in) to the topmost of the two broad tracks beside where you are working. This is now correct. With a wire link, link pad 3 to the lower of the two broad tracks. Check that you have no solder bridges, and that you have in fact cut the two broad tracks connecting from the top edge direction to pads 1 and 2.

You can now complete the board according to the instructions. Wiring up the 24 way umbilical is a bit tricky, but there is just enough wire for another go if you are careful.

With the board assembled, you now need to turn you N1 board over to make a few links on the back. Before doing this, it is advisable to unplug it, and to remove IC15, & IC16 which will both be required on the Econographics, and also IC20. The few links are easily made, but if you are in any doubt, get a second opinion that they are correct, and that there are no solder splashes or bridges. (Character generators come expensive – like 10.00 each!) Replace IC20 on the N1 and insert all other i.c.s into Econographics.

Page 19 of 71