Let’s start our series on T/S reliability improvement with some simple but effective ways to make your basic machine virtually crashproof. If you’ve been using your machine for a while you’ve probably had times when the computer suddenly dies and nothing short of starting over will bring it back. I won’t belabor how annoying this can be, suffice it to say that with only a few hours tinkering you can make your journey through computer-land a lot less frustrating. We’ll concern ourselves with projects that are easily do-able by anyone with the simple mechanical skills with hand tools and a soldering iron; our first two projects, in fact, don’t even involve soldering, yet can upgrade your system’s reliability considerably. So you don’t have to be a hardware whiz to customize your TS1000/ZX81, though of course at least some kit-building experience is recommended.
The most common (and most publicized) cause of hardware crashes is the “wobble & die” RAM pack wiggle syndrome. As a result there have appeared a great many fixes for this, and we will assume that you’ve already secured this source of trouble one way or another. If you just recently got your machine, there are a number of products available to cure this, including straps, formed lucite supports, etc. The point behind it is in all cases to prevent the RAM from moving relative to the computer, which causes momentary bad connections to the edge connector. This way of connecting to PC boards was designed and works great for cards that are mechanically secured and aren’t moved except for service. Reliability suffers, though, if this type of connection is moved even a little bit due to the play between computer and RAM board. This simplest fix is to use “sticky foam” or velcro to semipermanently secure the RAM case to the computer ease. With sticky foam it may take more than one layer, and don’t be too chintzy with it or you won’t get the strength you need. Or you can get fancier with brackets or entire workstation layouts. Since the exact cure depends on whose RAM you have as well as your tastes and abilities, we’ll leave this up to you and go on to secure the next source of hardware crashes – the all-important power connection, and while we’re at it, the cassette plugs.
Plug Guard
You may have noticed that the power connection to the T/S machines is somewhat flimsy and prone to sudden death if it gets pulled by a tug on the cord or in some cases, even if it gets bumped the wrong way. So here’s a way to guard against this possibility. Figure 1 shows a way to do this using a 1-1/8″ x 2-1/8″ piece of lucite or aluminum, 1/43/8″ thick. Three 3/8″ holes are drilled to match the spacing of the power and cassette plugs, and three perpendicular tapped holes allow for machine screws to lock each plug in its respective hole. Even if you don’t attach the block to the computer, the three plugs are locked together as one assembly, making them much more reliable. Or you can drill two small holes as shown to screw the block to the upper computer case-half for the ultimate in security; the plugs can still be removed easily by loosening the set-screws, but when they’re in and locked you can be sure they’ll stay in under reasonable jostling.
Making the block won’t be a big deal for you if you have machine-shop access and experience. If you’re using lucite, you should have a circular saw and a lucite blade, and some experience or willingness to experiment with lucite; it binds easily so take it slow. Also take your time drilling, whether you use lucite or aluminum. You need a drill press and a good vise; a hand drill won’t be accurate enough. Mark the holes carefully first then drill a hole with a 1/16″ bit. Work up to 3/8″ a size or two at a time to preserve accuracy as much as possible. If the holes end up incorrectly Spaced or askew, the plugs won’t fit properly and you’ll damage the plastic jacks if you force them.
The dimensions shown work with the cords that came with my machines, but it’s conceivable that it won’t be right for yours, as these were apparently obtained by Timex/Sinclair from various suppliers. If this is the case, your best bet is to change the plugs to standard plugs like Switchcraft 750, available at virtually every electronics parts jobber. (Radio Shack also supplies a “clone” of this part.) These also fit more snugly than the molded type and are repairable if they develop a loose connection.
If this sounds like its beyond your means, don’t despair. Quite probably you know someone who could help you out if you ask nicely and maybe supply a six-pack. You might check out the small machine shops in your area. You may find someone to help you out for a token charge. If you have a lucite specialist in your area, he’ll probably cut you the block from scrap and even do the holes at a bargain rate if he’s not too busy. (And as long as you don’t make a pest of yourself!)
If you want to permanently mount the plug guard to your computer, include the mounting holes on the guard and use these to mark where the holes should be on the computer with the plugs in place. CAREFULLY drill small (1/16″) holes in the case and attach the guard with two, #2 x 1/2″ self tapping screws, Do the final tightening with the plugs in place. You may have to file out the plug holes a little to allow easy insertion and removal, depending on how accurately you drilled them.
Should you be in a position to manufacture a number of these, let me know if you’d be able to make them for others who may not be willing or able to do it themselves.
