TIMEX MAKES A CLEARER PRINTER
THE TIMEX 2040 thermal primer is the standard printer used with the American version of the ZX-81. The U.S. version of the Spectrum had yet to appear at the time of writing. It works with a different paper, 4.5in. wide plain white paper with a special coating sprayed on to the top of it. The coating turns black when heated, giving the impression of ink on the paper. It is much clearer and there is no difficulty with the paper sticking.
The case is 7.75 x 5.75 x 3.5in. high in moulded black ABS plastic and has a 6in. long cable at the back on the left-hand side. The connector to the end of the cable is bigger and more solid than the Sinclair version, having a half-inch hump at the top.
That hump contains two ferrite rings around the cable to reduce TV and radio interference and an interface IC - 74LS10. That IC helps to decode A7 and A2 instead of only A2 on the Sinclair version.
The case also has a metal comb protruding under the edge connector which prevents the edge connector wobbling and, presumably, the RAM pack, too.
Also on the back of the case is a power socket like that of the Spectrum but it requires 25V AC to run the printer. A transformer is supplied in a plastic case 2.5 x 3.5 x 2.25 in. with American-type power prongs on the back. There is no fuse or ventilation on the power pack and thus it becomes reasonably hot but it has not failed yet. The Sinclair printer is, of course, supplied through the computer and thus needs no extra power supply.
Inside the printer there are two regulators, one a transistor arrangement for the 25V DC supply to the heated pads which do the printing and a 7805 IC of the ZX-81 type fitted into a large heatsink and situated under a ventilation slot in the top. The power supply is set for 110V AC and therefore should not be used without a stepdown auto-transformer to convert the voltage from 240V supply.
There are two switch pads mounted in the top of the box which push two flat switches mounted on the PCB underneath; they turn the printer on and off. Pushing the off button while holding-down the on button puts the printer into a self-test mode, printing alternate lines of 1s and 8s independent of the computer.
The other electronics inside the printer are five driver ICs, one for the motor and four for the heated pads. There is also a pre-programmed ROM 8741 which controls all the printer operations.
The pads on which the printer depends are spring-loaded on to a rubber platen, like a typewriter, and are made of some ceramic material on which 20 copper wires have been plated. There are two pads and each wire will print over one character area, so theoretically there should be 40 characters but you get only 32. The pads move from side to side while printing, controlled by a nylon gear arrangement, so that 32 dots are printed at one time.
The printing head is then moved on to the next 32 until all eight dots on each character line have been printed before moving to the next line. The printing speed is very fast; on self-test you can print 124 lines a minute.
The paper roll used in the printer is inside a perspex cover and the start of the paper is pushed under the platen; the on button is then pushed to feed through the paper. The paper appears on the outside of the paper-holder on the other side of the kin. platen. The platen cannot be pushed in reverse, so the only way to free jammed paper is first to cut it and then push the platen forward, using the motor drive if possible.
The printer is considerably easier to use than the Sinclair one and the paper is much cheaper at $1.50 (£1). The printer costs $99. The one tested was sent by a friend in the U.S. and it cost $99 plus $23.90 postage - £81.67 - plus £14.13 Customs duty, a total of £95.80.