I’ve decided to step out of my comfort zone and grab a soldering iron. First I practised by desoldering a couple of CPUs and installing sockets which was my first time using a desoldering station. One time long ago I tried using a desoldering pump but I haven’t got the ninja skills required to use it so the desoldering station was a Godsend and a game changer.
Now that desoldering ICs was less of a problem, I had a go at recapping a 48K motherboard and since majority of those challenges turned out moderately successful I thought it was time to attack an entire motherboard and give it a good overhaul.
The Spectrum I picked was one I acquired last year.
I felt like something a bit different and a bit more special so went for issue 4A motherboard of the yellow variety. They’re not really what you’d call “L@@K R@RE” – they’re unusual but fairly easy to find if you know where to look for it. And they are very pretty to look at; with blue rather than white silkscreen markings like on every other motherboard version.
No Spectrum collection is ever fully complete without at least one yellow type motherboard. If you’re a hardcore collector you ought to have both types of yellow motherboard – issue 4A and issue 3B (assuming there isn’t a third type which hasn’t been discovered yet).
The job took most of the evening but since I’m merely a beginner it’s not really surprising. I was being closely supervised by my master who can do all this in a space of an hour with closed eyes so I’m quite lucky to be his apprentice and have access to professional tools. Everything went smoothly and there was no major cock-ups on my part.
Here’s what was involved:
First I have performed a composite video modification so that I could easily check if the motherboard was healthy by connecting it to TV (which luckily it was). I used a piece of simple telephone wire. It does the job just as well as using a smoothing capacitor or a transistor – neither makes any difference in my experience.
Then I replaced all electrolytic capacitors. I used high quality Vishay brand axial capacitors to keep the look as close to original as possible. Many people choose cheaper brand black capacitors but colours matter to me a great deal and I think black caps ruin the pretty look of yellow motherboards and also irritate my OCD.
Next I got rid of the power regulator and replaced it with a switch-mode DC converter. It allows a low power consumption so the huge metal heatsink was now redundant. In an effect the Spectrum won’t be overheating and in fact will hardly get warm at all even after being on for hours.
Last but not least, the ULA chip needed a heatsink to help cool it down and stop it failing from overheating. Owing to limited space inside a rubber-keyed Spectrum case, in order to fit a heatsink onto the ULA the socket had to be removed and the chip soldered down directly onto the board. I’ve never operated on the ULA area before but having desoldered CPUs and installed CPU sockets it seemed like the same trick but in reverse. It’s worth doing to help protect a precious ULA life.
Now that the internals have been serviced the exterior was in need of some attention. Refurbishing the case is my usual line of work but the Spectrum was in fairly good nick to start with so it was an easy task. If you own or have seen a large number of Spectrums you will be aware of variations in faceplates, rubber mats and cases. Whenever I refurbish a Spectrum I try not to mix in parts from other Spectrums unless they’re of the identical type so that the Spectrum remains in as close to original setup as possible. Not that many people notice or care about the subtle differences, but when I see a “refurbished” Spectrum which has been fitted with parts from other models that don’t belong it gives me a serious OCD itch and it stops me from purchasing such machine.
Having said that, there isn’t a strict guide to what type of faceplate/keymat belongs to what type of Spectrum. Some models always feature the same type of exterior and others can vary a lot. This one is one of the latter. If you ever come across another Spectrum with a similar serial number or even a yellow 4A motherboard inside, the chances are it will have a totally different keymat/faceplate. But nonetheless I like to keep the same parts in the Spectrum before and after the refurbishment.
The one thing that is almost always an obligatory part of a Spectrum refurbishment is the keyboard membrane replacement. I have been stocking my membranes for years from this supplier.
The membrane replacement can be the simplest or the most daunting task in the world, depending on how easy your faceplate comes off. Luckily the faceplate in this Spectrum is held down by metal tabs rather than a sticky tape/glue which makes the removal a piece of cake. The metal tabs allow you to remove and insert the faceplate as many times as you like without a risk of damaging or bending the faceplate in the process.
While the faceplate is off and the case fully disassembled this is the perfect time to give each individual part of the case a good clean. There are many methods of doing this, but nothing beats a warm soapy bath. Don’t be afraid to use a washing up brush to scrub up the case or a washing up sponge for more delicate parts such as faceplates. Baby wipes can be used afterwards to remove leftover dirt residue stuck in the crannies or clean parts of the cases that have stickers on them which you want to stay on. Remember to allow all of the components to dry thoroughly before re-assembling. A kitchen towel will speed up the process if you’re in a hurry. If your Spectrum has a delicate light grey keymat exercise caution when cleaning or risk parts of the white/red lettering peeling off.
When the case is thoroughly cleaned inside out finish the job by taking care of little details such as replacing rubber feet if any are missing or repainting the white ZX Spectrum logo if faded.
You will notice a small melt mark just below the serial number. It cannot be removed but like the stickers it’s part of the Spectrum’s history. The mark was caused by a connected Interface 1 expansion where as a result of a design flaw, a component inside the IF1 heated up causing a melt mark which has spread onto the Spectrum’s casing.
So this was my first ever fully refurbished Spectrum. A part of me wants to keep it but it is with regret that I don’t have place for this little guy in my collection and need to cut down on the number of Spectrums with yellow 4A motherboards I own. And now that it has been freshly serviced it deserves to be free and to be loved by someone else as with such a large and growing number of Spectrums in my collection it’s not practical to keep more than 1 or 2 of the same type.
So the Spectrum is up for adoption and looking for a new loving home. Don’t forget to use discount code “yellow” for 10% off.