What Are The Common Problems With The Rubber Key Sinclair ZX Spectrum and Spectrum +?

The Rubber Key Sinclair ZX Spectrum

In 2022, the Spectrum will be 40 years old. It was originally released on St. George’s Day, 23rd April in 1982.

So what are the most common problems with the first two models? This article looks at four of them:

  • The Keyboard Membrane
  • The TV Display
  • The Electrolytic Capacitors and Power Circuit
  • The Spectrum will not boot to the white screen and Sinclair Research prompt

Before we start, please be aware that I offer a basic test, assess and first hour of repair service. If it takes longer, then I will let you know my assessment before doing any further work. This service is available for all models of Spectrum, and at the same cost – click here for more details.

Let me know what you are looking for, by getting in touch via the Contact form or contact details at this link here. I give discounts if you buy a bundle of products or services.

The Keyboard Membrane

A New and Old Keyboard Membrane on a Sinclair ZX Spectrum + (Plus)

By far the most common problem on a Sinclair ZX Spectrum and Spectrum +, is the keyboard membrane. You might be able to get the Spectrum to display the Sinclair Research prompt (see below), but the keyboard may not work at all, or some keys work and others do not.

This is because the keyboard membranes dry out, become brittle and fail with age. It is rare to find an original one that is fully working these days*. And if the membrane is working at first, it will probably not be long before it starts to fail when the Spectrum is started up again, with some keys not working or the ribbons breaking connections with the Spectrum’s printed circuit board (PCB). The ribbons may break when you open up the Spectrum.

In the first photo above of inside a Spectrum + case, the old membrane is shown on top of a new one. The new one has been fitted to the top of the Spectrum + case. The new one is shiny. The old one is dull. The second photo below shows the completed process of fitting the membrane.

The new membrane fitted to the Spectrum +

At PopeyMon, I offer a service to source and to replace faulty membranes with new ones and to service the keyboards on the later models of Spectrum. There is a service that I provide for each model of Spectrum here – click the link:

*There is one exception – those produced by Samsung were higher-quality and last longer. But even these can fail and must be checked.

This procedure is particularly tricky on the Spectrum + and on the Toastrack to get right, and to make sure that all keys are working. The membranes are also more expensive than for the rubber key models. And hence the price difference with the service between the rubber key and +/128k. A photo of the new membrane for the rubber key, being fitted for a PopeyMon customer during a full repair and refurbishment, is shown below.

New Keyboard Membrane

While I have your Spectrum, I can also perform other repairs and refurbishments. Read on for more.

The TV Display

A Sinclair Spectrum Running Manic Miner on a Modern TV using Composite Video TV Signal

Another common problem is that when the Spectrum was brought out, it was common for home computers (called “microcomputers” back then) to use the domestic TV to output their display, and to not use monitors.

TVs in 1982 used an analogue radio wave signal, which was normal for broadcasting TV in those days. There was no digital TV signal. And the TVs were cathode ray tube (CRT) designs.

So inside the Spectrum, there is a modulator box that converts the Spectrum display to Channel 36 UHF (Ultra High Frequency).

But in 2022, this is a problem because modern TV designs do not use CRTs. And the analogue TV signal has been replaced with a digital TV signal.

If you have an old TV, this is not such a problem. But CRTs are getting old and can cause problems with reliability and safety. They are high voltage and high current.

Some modern TVs allow you to easily tune to analogue signals. Others have a complicated menu system to navigate. And other TVs don’t allow you to even tune in to analogue at all.

Modern TVs also expect certain characteristics of the signal from the old computers and the computers just cannot live up to the expectations.

So while you can do it “the old way”, it is advisable to use the composite video signal that was always generated by the Spectrum and then converted by the RF modulator. You just ignore the RF output and by-pass it.

The composite video modification is another service that I provide at PopeyMon. You can buy it from the shop by clicking here.

The Electrolytic Capacitors and Power Circuit

An Issue 3B Spectrum PCB Repaired and Refurbished by PopeyMon

A common problem in old electronics is that electrolytic capacitors can fail. Age, storage conditions, usage patterns, heat and other factors can mean that they can dry out and deteriorate from their function of storing charge. This can impact on the performance of other components in the Spectrum, and even stop it from working completely.

Of particular concern inside the Sinclair-era models of Spectrum is the DC-DC conversion power circuit on the right-hand-side of the PCB in the photo above. This power circuit is notoriously unreliable and has caused many repairs to be done. It has also damaged other components, such as the lower RAM chips that are required for the system to start successfully to the Sinclair Research prompt.

The power circuit was revised and revised again in later issues of Spectrum PCB. When Amstrad took over the Sinclair brand, it was removed completely from the Spectrum PCB and put in an external PSU.

This wise decision by Amstrad did not solve all of the issues in the later models of Spectrum, but it solved some of the problems on the computer PCB. I have other articles on this website about the models of Spectrum and a whole series of article about the PSUs. I also sell all models of Spectrum and PSUs in the PopeyMon shop.

Why have I mentioned the power circuit in relation to the electrolytic capacitors? Because the power circuit is essential to the operation of the booting of the Spectrum. If the power circuit is not producing the correct voltages, then your Spectrum will not start up properly, if it starts up at all.

So if the capacitors in the power circuit are failing, then this can mean that the power circuit is not working correctly and your Spectrum fails. It can damage components that are particularly difficult to replace.

It is therefore wise to perform checks before starting up a Spectrum. I can perform these checks and more for you, when you send me your Spectrum.

I offer a service to replace all electrolytic capacitors with brand new and quality new ones – click here. While this may not fix all types of problems, it can prevent some problems from occurring now and in the future.

The Spectrum Doesn’t Boot to the Sinclair Research Prompt

SPECTRUM START SCREEN

If the Spectrum does not start up to the white screen and Sinclair Research prompt, then there is a problem. When the Spectrum starts up, it performs a self-test and if the test is successful, you get the prompt. Possible causes could be the power circuit as described above. It could also be a host of other problems. If you cannot get all keys to work, then it is probably the keyboard membrane, as described above. If you cannot get a TV display, then the section above describes possible causes.

I offer a basic test, assess and first hour of repair service. If it takes longer, then I will let you know my assessment before doing any further work. This service is available for all models of Spectrum, and at the same cost – click here for more details.

Let me know what you are looking for, by getting in touch via the Contact form or contact details at this link here. I give discounts if you buy a bundle of products or services.

Thanks for coming to PopeyMon Games and Fun for all your Spectrum needs.

Sinclair ZX Spectrum Power Supplies – What Types Are There (Part 6)? – The First One? UK1200?

When I started doing the research, opening up lots of Spectrum power supplies, and writing this series of articles, I had thought that the UK1400 power supply was the first one for the Spectrum, as shown below.

Power Supply for Rubber Key and Plus Types of Sinclair ZX Spectrum

But I was told by members of the Spectrum community that there was a UK1200. I had never seen one in the flesh… UNTIL NOW!

I have got one NOW! How exciting!

Model name: UK1200

Input: 240V AC

Output: -12.5V DC approx., unloaded (unregulated), maximum current rating 1.2A (1,200mA and hence the name UK1200).

When under load and being used on a Spectrum, the voltage will be nearer to what is stated on the PSU label.

Polarity: Centre Negative (not positive) Outer Positive (not negative as on most barrel connectors).

Getting the polarity is essential if you do not want to damage your Spectrum.

I do not know whether the UK1200 power supplies are suitable for any other model of Spectrum than the Issue1 Spectrum.

The strain relief on the PSU is not as stiff as on the UK1400. This might mean that it lasts longer because they are notorious for breaking.

It has a barrel connector that is not smooth. The UK1400 that was subject to a safety recall had a smooth barrel and black and white DC cable.

The insides are very similar to the UK1400. It is a full wave bridge rectifier with two smoothing capacitors. And a fuse.

I cannot verify that it the UK1200 would work on an Issue 1, because I do not own one.

However, the fact that the UK1400 power supply followed the UK1200 – or even possibly was being sold at the same time as the UK1200 – suggests that 1.2A was insufficient for the Spectrum and 1.4A was needed.

The UK1200 certainly won’t be suitable for the 128 “Toastrack” and not the (Amstrad-era) Spectrum +2 Grey. This is despite the fact that the DC (computer side) barrel connector will fit on these later models of Spectrum.

I would not recommend running any Spectrum with the UK1200 and without an Issue 1, I have no intention to!

And sorry. This power supply is not for sale.

But I do have a range of other power supplies for sale. The series of articles on this website is there to help you choose the right one.

Before use all power supplies need to be checked for safety, as well as functionality and that they are delivering the right voltage levels, current and polarity. So please note that they must be checked before use, and check the Safety article.

If you are looking to buy any power supply or want one checked, please get in touch. I will happily sell you one – fully tested and working – for the Spectrum 16/48k/Plus, for the grey +2 or the black +2 or +3. I also have a lot of other Spectrum parts, working computers and games for sale. I will happily put together a custom bundle for you.

I would like to credit and highly recommend the excellent videos by “JoulesPerCoulomb” on Youtube. “Greetings and good time of day…” to whoever this mysterious but extremely helpful man, is. His video on power supplies was a brilliant starter a few years ago to the many hours of research that I have conducted since on Spectrum power supplies, and which I present in this series of articles.

A Look Inside the Original Spectrum Power Supply (16/48k Rubber Key Models)

The UK1400 PSU
The UK1400 Power Supply Unit (PSU)

On this PopeyMon Games and Fun website, in a series of articles I have tried to described all types of power supply unit (PSU) for the Sinclair ZX Spectrum models.

This goes from the first 16k and 48k rubber key models when the Spectrum was owned by Sinclair to the final disk drive version of the Spectrum, the +3 under the ownership of Amstrad. There is an index to the articles, as Part 0 of the series.

In this article, I am delving into the inside of the original Spectrum power supply, the UK1400 model.

I say original, but I’ve been told from several credible sources in the Spectrum community that the Issue 1 Spectrum had a UK1200 model. Until I see one being used on an Issue 1 Spectrum “in the flesh”, I will still call the UK1400 the original Spectrum PSU.

The UK1400 was used for all rubber key models of the Spectrum – 16k and 48k. It was also used on the Spectrum Plus with a different design.

This earlier article also talks about the UK1400. But I want to go a bit deeper here. Here are six images of the components inside the UK1400. As in the earlier article, there are several designs of the UK1400.

They are all implementations to the same specification. And all of them use a full-wave bridge rectification circuit to convert the mains 240V into around 12-14V DC (unregulated and when unloaded) via a barrel connector to the Spectrum board.

Note: A “smooth” barrel connector has been used to replace the original on the photo at the top of the article. Please see the Safety Warning article for more on the UK1400 production that were recalled for safety issues.

Each of the designs meet the UK1400 PSU Specification in different ways.

Some designs are compatible with other designs and some are not.

There are different orientations of the PCB and transformer – some designs have the PCB underneath the transformer and other designs have the PCB at right-angles and to the side of the transformer.

There are different versions of the case, so they are not interchangeable with different designs. Here is one case from a PSU that failed its tests.

And as I have said on other articles, BEFORE you plug any power supply into your beloved Spectrum, please CHECK is it safe to use: (i) for you, (ii) for your Spectrum.

I have TESTED and WORKING PSUs for sale in the PopeyMon website shop and in the eBay popeymon shop too.

If you have any questions, please get in touch.

How Many Sinclair ZX Spectrum Power Supplies Are There?

Two Designs of the UK1400 PSU

This is another article on Spectrum power supplies in the PopeyMon Games and Fun series of articles.

In the photo above, there are two different designs of the UK1400 power supply unit (PSU). This was for the 16k and 48k rubber key Spectrums. As described in more detail in Part 1 of the Series and Part 3 of the Series, the UK1400 can also be used on the Spectrum Plus.

In the photo are two similar designs. But they are not identical. Can you spot the differences?

Spectrum UK1400 with Transformer on Top

Several other designs also exist, including designs where the transformer is on the top of the PCB, instead of next to it (see photo).

The cases can also differ on the inside, meaning that different designs may not be interchangeable. There are also variations in the capacitors, in the number of capacitors and even the polarity of the wires to the DC cable can be swapped, with respect to the colouring on the wires.

So what seems to be the same PSU from the outside, can be quite different on the inside.

Unless you have owned the PSU ever since buying it, you may not know what has happened to the PSU since it was manufactured. It may have been looked after in the original polys, and lovingly cared for during the last 35 years. Or it may have lived in a damp cellar, being damaged in bad conditions and affected by temperature variations and damp. It may have been dropped from a great height onto a stone floor.

You just don’t know!

And there is also the official Sinclair Safety Warning for one of the designs to consider, as described in this article here.

So using and tinkering with power supplies can put your Spectrum and more importantly, your health and safety, AT RISK!

You should check your power supplier is the right one, and that is safe for you and your Spectrum.

So unless you know what you are doing, please seek professional help.

PopeyMon Games and Fun has refurbished and sold many Spectrum PSUs.

Please get in touch and we can provide a refurbished power supply or repair yours.

There are more types of Spectrum PSU:

Please click on the links for more info on each power supply, and which can be used with each model of Spectrum. The general advice is that as each Spectrum was released, the power requirements increased. So earlier PSUs tend to NOT be compatible with later Spectrum models. In any case, the power connectors changed on the Black +2 and +3.

Thanks for coming to PopeyMon Games and Fun.

Spectrum +2 (Black) PSU

Sinclair ZX Spectrum Power Supplies – What Types Are There (Part 2)? – The Toastrack

The much sought-after Sinclair ZX Spectrum 128 “Toastrack”

There are several types of Sinclair ZX Spectrum. So it follows that there are several different types of power supplies for the Sinclair ZX Spectrum.

This ranges from the rubber key 16k and 48k models, then Plus and 128 models during the Sinclair ownership of the Spectrum brand, through the Amstrad ownership of the Spectrum brand (after Alan Sugar’s Amstrad bought the rights to the Sinclair Computer brand), to the present with the new Spectrum Next.

Part 1 of the PopeyMon articles on the types of Spectrum PSU talked about the rubber key models and the Spectrum Plus.

This article (Part 2) talks about the only 128k Spectrum of the Sinclair era – the Sinclair ZX Spectrum 128 (a.k.a. “Toastrack”).

The Toastrack computer looks very similar to the Spectrum Plus, but has a huge black heat sink on the right-hand-side of the case. Hence the name, the “Toastie” or “Toastrack”. Inside, it is quite different, as well as the obvious extra RAM.

The left and right hand sides of the Spectrum 128 Toastrack
Power Supply for Rubber Key and Plus Types of Sinclair ZX Spectrum

The power supply (PSU) shown in the photo above is a UK1400 model, which is OK for use on 16k and 48k rubber key models. The one below is the Spectrum Plus version of the UK1400.

Like the computer itself, there is a similar look of the Plus PSU and Toastrack PSU.

Spectrum Plus version of the UK1400 Power Supply

None of the UK1400 power supplies are suitable for any other model of Spectrum – not the 128 “Toastrack” and not the (Amstrad-era) Spectrum +2 Grey.

This is despite the fact that the DC (computer side) barrel connector will fit on these later models of Spectrum. And despite the fact that the Spectrum Plus UK1400 looks very similar to the Toastrack PSU.

Why? Because the power requirements of the Toastrack and Grey (subject of a future article) are higher than the 16/48 and Plus. They require more current than the UK1400 can deliver.

The UK1400 model is called the UK1400 because it delivers a maximum of 1,400 mA (milli-Amps). Or put another way, 1.4A (1.4 Amps).

The Toastrack needs more than 1.4A.

The Toastrack power supply can deliver more current. It can give 1.85A. This is why it is called the UK1850. Here is a photo:

Spectrum 128 “Toastrack” Power Supply

You can see in the photo above that the case has the textured right-hand-side, which is different to the Spectrum Plus UK1400 PSU.

Underside of the Toastrack PSU

On the underside of the PSU, you can see in the photo above that the model number is UK1850 and the maximum current is 1.85A. The quality of work inside seems to be higher than in some of the UK1400 models.

The official Toastrack power supply is becoming hard to find now, especially in a decent condition. This is the only one that I have, at the time of writing. So I have not been able to do a comparison of the internals, like I did in Part 1 with the UK1400 model.

This Toastrack PSU needs some work to clean it up and to replace the mains cable, but it has been tested including an electrical safety (PAT) test and it is working. The PAT test failed due to a nick in the mains cable insulation, so it would not be for sale in the PopeyMon eBay shop until that was fixed. But it’s the only I have, at the time of writing!

If you are looking to buy any Sinclair power supply or want one checked, please get in touch.

I will happily sell you one – fully tested and working – for the Spectrum 16/48k/Plus, for the grey +2 or the black +2 or +3. I also have a lot of other Spectrum parts, working computers and games for sale. I will happily put together a custom bundle for you.

I will be writing more about more Spectrum power supplies in the near future. Watch this space! Part 3 is now here.