Relishing Retro Computing: Restoring A Sinclair ZX Spectrum To Full 1980s Glory – Info Gadgets

Like many of my generation the 8-bit microcomputers of the were a defining aspect of my childhood and adolescence. Playing games wasn’t just a solitary experience; it was a shared interest that drew friends together and gave a sense of involvement in a community. The fun of games helped nurture an interest in how the machines worked and how to write programs. This set the scene for my future career path and has led to a lifelong fascination of technology. I’m grateful to my parents — and my brother — for supporting me in this journey in my early years and spending their money on computer equipment that at the time they could ill afford. Their love, practical support and selflessness in my childhood has in no small way led to so many positive impacts on my working life and indeed in life in general.

Feeling nostalgic I decided I’d start a small collection of the machines that had had the most personal impact. When I was a kid, my cousin owned a ZX 48K which he’d bought it brand new in 1983 and which, when I was around 14 years old, he’d loaned me on a long term basis. I asked him if he still had it and, if so, would he sell it to me. Sure enough, he had it carefully packed away in as good condition as you could possibly expect for a 35 year old machine. He even had all of his tapes, many of the inlay cards contained my hand writing and that of my school mates!

A machine that is 30+ years old needs some care so I set about learning what maintenance would be necessary. This is a short write-up of what I did which hopefully you’ll find interesting; but at the end of the day, its primary purpose is to document the process so that in years to come I can remember it myself.

I should say that I am a rank amateur in this field. Although I’ve soldered a few things in my time — including building my own Sinclair ZX81 when I was 12 (it saved £20 off the purchase price) — before tackling the Spectrum, it had been 37 years since I last took a soldering iron to a computer circuit board! There are a wealth of resources on the Internet from people who know a great deal more than me so I approached the task with humility and a willingness to learn — and not without a doubt or two, I must admit. If I can do it, so can you.

Restoration

My cousin delivered the Spectrum, in its original box with all accessories, and it was in phenomenal shape. He sure takes care of his things. On powering it up it worked but a number of keys were dead. This isn’t surprising as the keyboard membrane is pretty much guaranteed to degrade with age. I set about learning more about Spectrum restoration and what follows is what I learned and what I did.

Here’s what we’re going to walk through today:

  • Replacing the keyboard membrane.
  • Upgrading the voltage regulator.
  • Modifying the video output to composite video rather than RF (making it easier to run the machine on a modern TV).
  • Renewing electrolytic capacitors.
  • Tidying up and refitting everything back together.
  • Testing and enhancing your 8-bit gaming experience!

The one piece of advice that applies throughout is to do one thing at a time and to test the machine at each step of the way. That way if it doesn’t work, you can be pretty sure the last change is the problem. You can power up without the keyboard connected so don’t be afraid to do that.

I’d also suggest obtaining a good soldering iron with an appropriate bit. I used a bit with a 1.3mm wedge shaped tip. From what I read, it’s advisable to use a temperature not in excess of 300º C. Also, get a good de-soldering tool and de-soldering braid is very useful, too. Check out YouTube videos on how to use all of these things and on soldering and de-soldering techniques in general.

This is what my Spectrum’s PCB looked like before I started work. You’ll see in this post how it changed as I applied various modifications.

The PCB its original state.

Before I get into the detail, a tool which I found essential was a magnifying headset. It’s not just ZX Spectrums that deteriorate with age as my eyesight isn’t what it was 35 years ago either.

Keyboard Membrane Replacement

It turns out that replacements are easy to come by. I bought one through SellMyRetro for £9 including delivery. Fitting it is the tricky part, or rather removing the old one can be fiddly and time consuming. There are lots of YouTube videos out there on how to tackle the process. Here’s one I found useful. What I would say is get a set of plastic trim removing tools. I’ve seen videos in which people use screwdrivers to help prise the aluminium keyboard face plate from the plastic case, which to my mind is guaranteed to cause damage to both the face plate and the case. Here are the tools I used, which are cheap to buy from Amazon or eBay:

Plastic trim removal levers make life easier removing the keyboard face plate.

I found the trick was to start from the sides, inserting the tool between the case and the plate. Don’t be afraid to use a fair amount of force but do so in a careful, controlled way. Once the tool has started to prise apart the surfaces and is inserted by maybe 5mm or so, slide it across to start to break the seal. Push in a little further and repeat. It is extremely easy to kink the thin aluminium plate so care is definitely crucial, as is patience. It takes a while but you know what they say about a stitch in time. If the plate is already in bad shape or you damage it, never fear because you can buy replicas. I toyed with this idea but as my plate was in near perfect condition and because I was going for restoration not perfection, I stuck with the original. Once you’ve carefully removed the plate it will look like this.

Freshly removed face plate, complete with residual glue gunk.

A rag, IPA and patient and careful rubbing will remove the old glue. This is one of the most tedious parts of the process. It takes a long time and if you don’t take care there are ample opportunities to cause damage. Try in particular not to get too much IPA on the painted side of the plate. A little will be okay but if you rub hard you’re risking rubbing off paint. After I’d finished I rinsed it with cold water and patted it dry. Remove glue gunk from the plastic case as well but be careful not to get IPA on the exposed parts of the case as it will very likely strip the lacquer.

The keyboard face plate, cleaned with IPA and looking spick and span.

To remove the membrane itself, remove the case by unscrewing the five screws which hold the case together. Carefully hinge it open from the front and reach in and carefully pull out the two ribbon connectors. What you see will be as below (this is a different machine to the one I restored, BTW).

Peering inside the case — the left hand side keyboard connector.
Peering inside the case — the right hand side keyboard connector.

Remove the rubber mat and the old membrane and replace it with the new one. Now’s a good chance to clean things up of course. The rubber mat will likely have accumulated much crud over the years and would probably benefit from a good clean. I used warm water with a very dilute solution of general purpose household cleaner followed by a rinse with cold water. Re-connecting the membrane is a matter of pushing the ribbon connectors back into the sockets on the PCB but there’s more work to be done so leave that for now.

The face plate will need to be re-glued but if I were you, I’d wait until right the end of the job just in case something goes wrong! We’ll come back to that in a while.

Voltage Regulator

When you open up your Spectrum you’ll notice there’s a large piece of aluminium bolted to the board. This is attached to the voltage regulator. Because the linear voltage regulators of the day were only around 40% efficient they got pretty hot and needed a heat sink to dissipate the excess heat. Today, switch mode regulators are 90% or more efficient and they’re easy to obtain and to replace. At 90% efficiency, there’s no need for the heat sink so you can remove it completely.

I ordered a TRACOPOWER TSR 1–2450 regulator from RS (RS stock number 666–4379)

For detailed instructions, see this blog post from Tynemouth Software.

Here’s how my PCB looked when the replacement was complete. Much neater with all of that metalwork gone!

PCB with new switch mode voltage regulator.

Video Modification

If you’ve attempted to connect a vintage computer to a TV you’ve probably discovered it can be painful. What with the switch to digital, at best a modern TV isn’t designed to make it easy to hook up a 30+ old computer and at worse it won’t even have an analogue tuner.

A good solution is to modify the Spectrum’s output to produce composite video which should connect to any modern TV; besides which, it alleviates the need to tune the TV to the Spectrum’s signal. Even if TVs drop composite input in the future, it seems likely that composite to HDMI adaptors will be available for a long time to come.

Obtaining the necessary parts is easy. I bought a kit from Retroleum that contained not only the necessary video mod components but also the replacement capacitors for the PCB (see next section). If you want to buy them individually from RS or a similar source, you can do that too.

To apply the modification I followed the “capacitor version” in Retroleum’s blog. A summary of the process is:

  1. Remove the modulator lid and de-solder the resistor connected to the phono jack.
  2. De-solder the two leads on the left hand side which connect the modulator to the PCB.
  3. Solder the capacitor’s +ve lead to the PCB and thread the -ve lead (the one with the white stripe on the capacitor body) through the grommet to the phono jack (where the resistor was originally connected).
  4. Fold the modulator’s original leads up and over and replace the lid, trapping the wires so that they’re secured out of the way.

Now power up the machine, connecting it to the TV’s composite video input, via a suitable lead of course, and check it works. Here’s how things looked at this stage.

Composite video modification.

I also elected to replace the transistors TR1 and TR2 with the BC549C transistors provided by Retroleum. It’s up to you if you decide to do the same. As they say in their blog remember that the replacements are oriented at 180º to the originals (I suggest keeping the originals, just in case you ever want to reverse the process).

Electrolytic Capacitors

It turns out that it’s not just the keyboard that’s is prone to failure after 30+ years. Replacement of the electrolytic capacitors is an essential aspect of Spectrum maintenance as if they fail, as they are likely to do, there’s an excellent chance that other components also be will be damaged.

There are some great guides out there on how to do this. Here are some I’d recommend:

You can buy the capacitors from RS or the like or there are various sources of kits. Here’s a good one: https://www.retroleum.co.uk/zx-spectrum-capacitors.

One key piece of advice is replace one at a time and test. That way if it doesn’t work, you know what you need to fix.

Tidying Up and Refitting

Once I was done, the board looked like this. Given I’d last soldered a PCB when I was 12 years old (37 years ago!) I was pretty pleased with the results:

PCB with modifications and maintenance completed.
PCB underside with modifications and maintenance completed.

If you’ve read the posts I’ve linked to and perhaps done your own research, you’ll have discovered that there are a few things that are worth doing:

  • Check the power socket and re-flow the solder if it looks necessary (i.e. if the joints look like they could be going dry). If the socket is worn it’s worth replacing. Retroleum sell replacements. (I did neither of these things as it all looked to be in good order).
  • Clean the edge connector with IPA.
  • Clean the board in general with IPA.

When you’re happy you’re done, replace the PCB into the lower part of the case and secure it with the single screw. Take the top part of the case, with your freshly replaced keyboard membrane, and hinge it from the rear. Reach inside and carefully insert the ribbon cables into their connectors. Click the case back together, replace the five screws and you’re done! Power it up and to check that all is well. Check that every key works as it should (just rest the as yet un-glued face plate over the rubber keyboard mat).

Testing and Enhancing Your 8-bit Gaming Experience

Loading games from tape is all very well but these days we can do better. Retroleum do an excellent card that allows you to store your games on a microSD card and load them in seconds rather than minutes. It’s a great piece of kit:

http://blog.retroleum.co.uk/smart-card-for-zx-spectrum/

It also has the facility to load up different ROMs rather than the Spectrum’s own and comes complete with a ROM image that provides diagnostic tools. I’d suggest running these to ensure all is well with your machine.

There are other similar devices available but I have no experience of them.

A good soak-test is well worth doing. I loaded up Scrabble and let the machine play against itself for a few hours and then re-ran the diagnostics. All was well!

And you know what? The Scrabble program is pretty damn good, achieving some pretty impressive scores. Not bad for 35 year old hardware and software. It would be interesting to pit it against a contemporary app.

And Finally…

Now that you’re happy that everything is working, it’s time to re-glue the keyboard face plate. For adhesive, after much searching I decided on 5mm double sided acrylic tape. It’s super thin and very sticky so is perfect for the job. Here’s how I positioned the tape.

Double sided tape applied to the top edge of the face place.
Double sided tape applied to the bottom edge and sides of the keyboard.

If your experience has been like mine, there’s a lot of satisfaction to be gained from tackling something outside of your comfort zone and skill-set and achieving a good result. I was particularly happy to be reunited with an “old friend” and to have restored it to its former glory and set it up for another 20 or 30 years of occasional trips down 8-bit memory lane. Some of the old games are hard to beat for playability and the priceless wave of warm nostalgia that they can invoke. They bring back memories of how life was back then and the friendships of that time, some of which I’m lucky have lasted and others, to my regret, have not.

Article Prepared by Ollala Corp

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