Spectrum Conversion
Today LCD would like to describe to you how you can install a Spectrum 128 with +D, etc., into a PC minitower case at low cost. Of course, this also works with a 48K, but the 128K causes more problems due to its size, while the +2A/B and +3 models are completely out of the question—at best, they might find room in a big tower case.
For the conversion, I used the Spectrum 128+ Euro version, not the Spanish or English one. The Euro version differs from the English one only by a single detail: the RS232/MIDI port is in the form of a DE-9 (Sub-D 9-pin) socket, and therefore has a larger cutout in the case. If you do not have this version—and it really is very rare—you will need to buy or make a converter cable if you want to use the RS232 interface.
Preparatory Work
After you have hauled the minitower case from the scrap yard or bought it from someone, the first work on the unit begins. First, loosen all the screws on the cover and remove it to gain free access to the inside. Next, remove the motherboard tray/mounting plate (two screws!). If there is still anything on it, such as a 486 or similar, throw it toward the nearest trash can with as much momentum as possible.
A minitower normally has two blanking plates for 3.5" bays and two for 5.25" bays; please do not throw these plates away if possible, as you can mount quite a few switches and that sort of stuff on them.
Next, remove the front panel of the case to get access to the MHz display. This should then be connected to the power supply, and using the trial-and-error method, set the MHz readout to 35 or 3.5. If you want to connect a Pentagon, you might as well set the turbo mode to 70 or 7.0 MHz. You make these adjustments using the jumpers located there, which, depending on orientation, light up a display segment when the turbo button is switched on or off.
Next, we can install the two +D disk drives, but don't forget! The connecting cable to the +D must not be twisted like on a PC or MB02! The drives should already be configured beforehand, to DS0 and DS1 (DS0=d1, DS1=d2). Then the power cables can be connected.
Next comes the keyboard. I used a DK'Tronics; you, however, may rewire a PC keyboard. I replaced the old and distinctly too-short DK'Tronics ribbon cable with a longer one and assigned a few extra wires: two for Reset, although that wasn't strictly necessary since the minitower also has a reset button. And two more wires for the snapshot button, which is then soldered in parallel with the one inside the +D. If you feel like it, you can solder two Sinclair joystick ports into the case or the keyboard, which should, of course, be decoupled using diodes. I did this as well, and on Sinclair Joystick 1 (parallel to keys 6, 7, 8, 9, and 0), I also installed two switches with which I can reverse the directions, which is sometimes necessary with certain Spanish games.
For a keyboard cable longer than 1 m, I recommend building a keyboard buffer (SUC-SESSION 130, Jan 1995).
Alright, that settles the keyboard question. Now we'll build a tape connection. For this, we need two 3.5 mm mono jack sockets and an old, unused mono cable with two 3.5 mm jack plugs. The cable is cut right in the middle between the two plugs and stripped, then we solder the ends to the sockets (shielding is ground!) and screw them tightly into the holes that we drilled either into the blanking plates or, even better because it's less obtrusive, where the PC brand badge used to be. Then the cable ends are marked with self-adhesive paper labeled "Mic" and "Ear"; the same can also be done on the case, either with self-adhesive paper or with felt-tip pens suitable for glass.
The LED from the +D can—but doesn't have to—be desoldered and mounted visibly on the case, or replaced with another one; the case's H-DISK LED is practically begging to be used for this.
The motherboard power connector is no longer needed, so we snip off a black and a yellow wire and attach them to a screw terminal block; you can tap 12 Volts from there. If you can spare a 3-pin terminal block, you can also snip off a red wire, which provides +5 Volts. So once again: Yellow = +12 Volts, Red = +5 Volts, and Black = Ground, i.e., the common negative terminal. The +5 Volts could then be used to drive display LEDs.
Since the old power supply brick is no longer needed, you can cut off the power plug with enough cable and use it later to connect the Spectrum; whoever prefers, however, can buy some cable and a new plug so as not to ruin the transformer. But before we ensure the power supply, there is quite a bit more to do.
To mount the Spectrum PCB in the minitower case short-circuit-proof, we must proceed as follows: Remove the old keyboard from the 128 and stash it somewhere safe—maybe we'll need it again someday—then disconnect the 7805 voltage regulator and loosen all screws. Once the PCB has been pulled out, unscrew the heatsink and place it with the old keyboard. Next, check whether the lower case shell fits smoothly into the minitower case and that there is enough room for the tape and RS232 connectors; there shouldn't be any problems with that.
Next, reattach the PCB and connect two Currah Microslots in such a way that the +D is angled toward the back, just as if it were lying flat over the keyboard where it used to be. That leaves two free slots, one of which should be used for a Kempston Joystick interface, because otherwise many games cannot be played. They simply demand a Kempston joystick. You can use a self-made interface built on stripboard for this, as described in SCENE+ issue 2/96; it is very flat and costs around öS 70-100,- to build yourself. Depending on where you buy the parts, it might be even cheaper. Interestingly, chip prices have shot up since Austria joined the EU. Whoever has the opportunity should therefore source the parts from Germany if possible. The joystick port should sit on a (ribbon) cable so that it can easily be routed to either the front or the back wall of the case, but we aren't that far yet, because first we have to test the individual distances inside the case, depending on whether you want to connect further interfaces.
The 128 is placed into the case with the edge connector facing down, and the motherboard mounting plate is put back in its old position. The interfaces should not touch the metal bottom; if they do, however, you can stick a piece of paper in between. Now you know roughly where to drill the holes in the motherboard tray so that they hold the Spectrum case. We mark these four or more spots with a felt-tip pen or pencil and remove the plate again. Then we place it on a piece of wood and drill with a size 3 drill bit until no more resistance is felt—which hopefully is the wood and not the floor! Once all holes are drilled, put the plate back in its old place and screw it down tight, then mark through the drilled holes where a hole needs to be drilled on the lower part of the Spectrum case.
Once you have the markings, remove all interfaces and the PCB again, and drill through the marked spot. Then pull the two parts tightly together with a screw to make them immobile; that way, the subsequent drillings will be much more precise using the metal plate as a template. Once you have all this drilling behind you, you have to insulate the screws, which are grounded to chassis, against the PCB. In the Euro version, the 128 has a plastic sheet or foil to insulate it from the silver interior; you can use that here. On the regular 128 and all other models, you must cover the screws with plastic adhesive tape (McGyver never manages without plastic tape either).
Then you may finally reinsert the PCB and screw it down. In this phase, the Microslots and the interfaces are added as well. If everything was measured correctly, the assembly can now be inserted without issues. Next, plug in the tape connections; this should also go smoothly. If you want to use the RS232, you need to run an extension to the rear, where above the bus slot covers there are metal cutouts in the shape of DE-9 (Sub-D 9-pin) connectors waiting to be knocked out or unscrewed, depending on the case model. On the Euro 128, a kind of joystick extension is already sufficient for this.
To secure the +D against vibrations, buy a perforated metal strip with many holes from a hobby shop, like the ones that used to be common in children's construction kits. There are several standards; I always use the version with a 15 mm hole spacing and a 5 mm hole diameter. That is ideal for the screws on disk drives or on the +D case.
The Microslot to which the +D will be connected should be sanded down on the right side so that the pull-tab won't get in the way when we screw the +D to the bottom of the minitower case using the metal strip. Alternatively, you can buy a Microslot without an enclosure from SUC.
Stand the minitower up so that the +D points with the bus facing downward, and adjust the strips on both sides so that they can be fastened on both sides with both screws. Bend the lower part of the strip at a right angle with pliers so that we can attach it to the case floor through one or more holes using two or more screws. Once both strips are properly adjusted, you can drill holes in the bottom panel of the minitower
...drill holes and fasten the rods to the +D and the case. If you measured something wrong, you can always drill additional holes into the rod. Now everything should be bolted down tightly and vibration-free, so we can move on to the power supply.
The Spectrum 128+ only needs a single supply voltage, which can range from 10 to 12 Volts. We can therefore use the 12 Volts tapped earlier directly, or step them down to 10 Volts using a 7810 voltage regulator. Do not even bother trying 8 Volts with a 7808; while it works on the 48k, you will not get a picture on the 128k. I used the 12 Volts directly, and everything works more than satisfactorily. The picture, which previously used to flicker from time to time, has now become very steady, so I can wholeheartedly recommend the 12 Volts without hesitation. When connecting it, do not forget that the positive pole is on the outside! For the connection, you can use the cable cut from the old power supply unit.
Anyone who has worked a bit with the 128k knows that the heatsink gets extremely hot at times—hot enough that you could heat your entire room with it in winter. For that reason, you should mount the old voltage regulator from the 128k that we removed onto a heatsink. It can be much smaller than the one in the Speccy 128, because it will be mounted in front of a fan later on, so there is no danger of overheating.
Next, we will do the reset connection. For this purpose, buy a pin header strip (which also comes in handy later as a keyboard connector for the Spectrum, provided you do not have the connection boards from DK'Tronics!) and snap off two pins. Solder the wires to their smaller ends, which will then be soldered in parallel to the reset button. But before you do that, you should slide a piece of heat-shrink tubing over the solder joints; in a pinch, tried-and-true electrical tape will also do. Once that is done, the connection to the little cable for the reset button on the minitower case can be made. The Spectrum's own reset button remains right where it belongs.
Now the disk drives can be connected to the +D, and the printer port can be routed to the back, to the knockout slot for a 25-pin D-Sub. That gives us at the back: 1x Centronics connector, so standard parallel printer cables can be plugged in (it might even be better if you could screw the printer cable down), 1x Kempston joystick port, and optionally 1x standard RS232 port. These can now be labelled, although that is certainly not strictly necessary. The keyboard can also be connected via a 25-pin D-Sub connector.
Now comes the fan, or if you prefer, fans—I installed two of them myself. For this, you will need those perforated metal strips again. Cut them to the proper length so that the fan can be mounted right above the board. The airflow should be directed onto the board to ensure the best possible cooling. The clearance above the board will be sufficient to mount the voltage regulator beneath the fan on a bent metal rod and a small heatsink, which in turn is fastened to a mounting hole on the fan.
The fan itself is mounted to the screw locations for the expansion slot brackets using the rods; they hold best in a triangular layout. The fan is attached to one of the free holes, while the opposite hole is secured to one of the transformer/PSU mounting holes. If the transformer does not have any holes—which would be unusual—you will just have to improvise. The voltage regulator must now be connected, preferably using a small extension cable (pin headers!). If everything is wired properly, it will only get lukewarm during operation, leaving more than enough cool air for the rest of the board, where the Z80 and the two ULAs need cooling. A second fan is recommended to blow fresh air onto the first one from the outside (through the front ventilation grille).
Next up is the TV/video connection. To connect a television, it is enough to run the TV lead to the outside of the case as an extension, or feed an antenna cable straight from the inside to the outside through the hole meant for the old PC keyboard socket—which is exactly what I did. In addition, the Video/RGB connector is also routed outside. For this, buy a DIN socket from an electronics shop, identical to the one on the Speccy 128 (or a 3-pin one if you only want a composite video output), along with a matching plug. Solder them together as an extension and mount it on the back of the case. If you cannot drill such large holes into the case, you can simply drill two smaller holes and mount the socket on standoffs—plastic spacer tubes will do, two of equal length through which you insert slightly longer screws. It might not look quite as professional, but it hardly gets in the way.
Finally, all that remains is to wire up the keyboard according to your own preferences, and the tinkering is finished. What is left to do is to test whether everything works correctly: keyboard, joysticks (all three ports!), drives, Centronics port (watch out: interference can sometimes cause printer glitches, such as dropped characters while others are printed twice), reset button, snapshot button, tape sockets, etc.
If everything works properly, you have done an outstanding job! The only two risky moments during this project are the soldering work on the +D when bridging the snapshot button, and desoldering the LED to replace it with a wire. Because the PC power supply is quite beefy and well-filtered, the Spectrum should now be much less sensitive to voltage fluctuations in the mains grid. For example, my Spectrum used to crash whenever I turned on an energy-saving bulb in my room. It does not do that anymore.
Another advantage is a longer lifespan thanks to better cooling. As you can see, the "all-in-one" solution does bring advantages that make sacrificing a few hours well worth it.
Disk interfaces other than the +D (Opus, MB02, Disciple) are too large and can only be connected with considerably more effort, if at all! I accept no liability whatsoever for damages of any kind resulting from misunderstandings or a lack of care. This guide was written to the best of my knowledge and belief; should questions or problems arise nonetheless, please call the club hotline (see the editorial).
I would be delighted if others sent in their own build reports here to share with the community.
Tiger's Claw
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