You’re just Multi-faced

A lot has been going on lately so I thought I’d update the blog with some of it. Starting with a small announcement. I secured the domain www.ProjectSPECCY.com It currently re-directs here. I am unsure as yet whether I will have a separate site or combine ProjectAVR and ProjectSPECCY here. Stay tuned.

On to the Multiface 128 recreation project. I have been attempting to find a source for an AT&Y SPEC-MATE which is a lesser known snapshot interface for the earlier Sinclair Spectrums. I used to use one back in the Spectrum’s heyday for hacking. Try as I might, I can’t find one for sale. I do know somone who has kindly sent me images of the device, including some good internal shots. This has proved difficult to copy however.

AT&Y SPEC-MATE

AT&Y SPEC-MATE

Whilst I continue my quest to find a SPEC-MATE of my own, I thought I’d investigate other snapshot interfaces. I have prototyped the Spanish Phoenix III (Phoenix IV) and added 8K of RAM to it in it’s second iteration, making it a Phoenix V for me. Both these devices appear to run the original Phoenix ROM and also the SPEC-MATE ROM but neither will return to the program called when the NMI button was pressed. I’m still investigating. The problem may be that I am working from someone elses tracing of the Phoenix III circuit. I can’t be sure it’s accurate.

Still wishing to investigate these interfaces, I chose to work with the Romantic Robot Multiface 128. The Multifaces were probably the highest profile snapshot devices around for the Spectrum (and Amstrad & Atari ST). At the time, they were always a bit too expensive for me. Now as an adult, I have managed to collect three different models, one each of Multiface 1, 128 and 3. I also purchased a MultiPrint which is a similar interface but based around printing rather than snapshots.

Tracing the Multiface 128 circuit was quite a long drawn out procedure. First physically following each connection and matching them to a circuit I drew in KiCad and then designing a PCB. However, I did so and the results are a working recreation of the device. Details and Gerber files are available on the Non-AVR Projects page. Anyone can download the gerbers and use their favorite fabricator to manufacture a PCB and build their own. I am not distributing the ROM image since it’s copyright status is unknown, however a quick search for ‘Multiface 128 ROM version 87.12’ should turn up a useful image. This will need to be programmed into a 2764 EPROM for use on the interface.

Recreated Multiface 128 in situ.

Recreated Multiface 128 in situ.

I am pleased to say that with the UK school term well and truly re-started, I have again been asked to help teach some of the students at St. Richards Catholic College I help a fellow Radio Amateur, Phil G3MGQ, teach radio at the Foundation level. The college was one of the few chosen to contact Tim Peake when he was aboard the International Space Station and some of the students at the college have been inspired to obtain their radio licences as a direct result.

I was extremely lucky in bagging one of the new vDriveZXs (review) from the first batch sold. I have a ZX Interface One and two Microdrives but the drives are faulty. I was looking into repairing the drives but now, one of them at least, will become a vDrive. I will retain the internals though, for study and spares. The vDrive is a module that fits inside an original Microdrive case and emulates the original using an SD Card. This enables up to eight virtual drives to be seen by the Interface One and, of course, since the SD Card has a much higher capacity, you can have multiple sets of virtual drives available. I am looking forward to receiving my unit and fitting it in one of my old drive cases. QDos to Charles Ingley, the creator.

Just to whet your appitite, I have a few other things up and coming in the Spectrum arena but at this time, I can’t say anything. Full details will be published here in due course.

 

 

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.6 Reassembly

It was finally time to reassemble the machine. I had one last cursory check of both sides of the board, just to make sure it hadn’t picked anything up that may cause an issue and placed the board in the lower case tray. I fixed it in with it’s single screw near the center.

ZX Spectrum PCB Back in the case lower half

ZX Spectrum PCB Back in the case lower half

One more check to see that the Upper RAM module was OK and then to plug the keyboard ribbons in. Typically, the keyboard ribbons are quite delicate so a lighter touch is required but in this case, the after-market membrane had slightly more substantial ribbons. I still took my time and made sure not to put too much pressure on them. Once the ribbons were in place, I placed the halves of the case together and inverted the machine to screw in the brand new set of screws I got from Retroleum.

New Screws In Place

New Screws In Place

It is important not to overtighten the screws, especially on an old case. When you are getting to the point where the screw is tightening, slow down and just tighten it enough to hold the case securely shut. Old plastic, especially if it has been left for years in a loft, will go brittle and it is really easy to break the screw colums or to strip the threads.

Also, from Retroleum, I purchased a brand new set of feet to really finish the job off.

Fitting New Feet

Fitting New Feet

At last, a fully refurbished 48K Rubber Keyed Sinclair ZX Spectrum!

Fully Refurbished 48K Rubber Keyed Sinclair ZX Spectrum

Fully Refurbished 48K Rubber Keyed Sinclair ZX Spectrum

The last step in this long process was to give the machine a test with one of my favourite games. I plugged in the ZX-HD and divMMC Future interfaces and fired up the Dell monitor. I loaded Batty and played a few rounds, all was well.

Testing the Refurbished Machine

Testing the Refurbished Machine

I hope this series has been helpful and enables collectors of older ZX Spectrums to maintain them in working order. Help in reparing these machines can be sought in two great Facebook groups, Spectrum4Ever and Spectrum For Everyone.

Series Index: Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum

 

 

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.5 Case Cosmetics

Now the Spectrum’s board was fully refurbed and tested working, it was time to turn my attention to the case, keyboard and fascia. The original fascia looked a little tired and was dented so I had ordered a replacement from ZXRenew It arrived well packed and in good time.

I found it quite easy to remove the old fascia which gave me access to the keyboard mat and membrane. The membrane looked as if it had already been replaced at some point and was still fully working. I put that aside for reseating later on.

Case and Keyboard Mat Cleaned

Case and Keyboard Mat Cleaned

It was then down to washing the keyboard mat and case, carefully in mild soapy water and rinsing off. I took my time, trying to rid the keyboard mat of accumulated dirt. The bottom of the case was quite easy but, on the top half, I found the glue that held the old fascia on to be a real problem. I tried various substances but in the end, I pretty much used my nails and fingers to rub it off. Not a pleasent job. Perhaps I should have waited until I had a suitable substance available but I was keen to finish the refurb.

After drying it all off, the next step was to re-ink the ‘ZX Spectrum’ text in white. I had managed to get the remnants of the old ink off and I now used a Extra Fine Tip White Ink Pen from Mutant Caterpillar to carefully re-ink the letters. It was no easy job. Because the letters had been worn over the years, the edges were not very defined. It took me several attempts. I am happy with the outcome, although I need a lot of practice if I’m to get results like @ZX_Priestess seems to manage!

Once I was sure the ink had dried, I replaced the membrane, keyboard mat and prepared to fix the new fascia on.

Keyboard Membrane Back In Place

Keyboard Membrane Back In Place

ZX Renew had kindly included some 3M branded fixing strips to use with the fascia. I applied these one at time and cut a shorter length to fill the gap on the front.

Fixing Strips Applied

Fixing Strips Applied

Getting the backing off of the strips proved to be challenging. Patience required! Once I had all the strips in place, I checked over the new fascia and prepared it to be fixed. I then removed the other side of backing from the fixing strips.

Ready to Fix On the New Fascia

Ready to Fix On the New Fascia

To avoid marks on the new fascia, I used a pair of cotten gloves I have lying around. The fascia fitted perfectly and I went around the edges checking it had made contact with the fixing strips. The left and right sides required a little extra persuasion.

New Fascia in Place

New Fascia in Place

I then moved straight on to the next step, the final assembly.

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.4 Custom Composite Video Mod

Now I had the Spectrum PCB fully working, I wanted to add a Composite Video modification to round off all the refurbishments. I had already used a neat circuit advised by Andrew Gostling when I repaired a previous machine.

Inverted Emitter Follower Composite Mod

Inverted Emitter Follower Composite Mod

Although that mod works fine, I wasn’t happy with the components being self-suspending. So I set about designing a PCB to house Andrew’s version of the mod, the more usual transistor mod and the simple capacitor mod.

Spectrum 48K Composite Video Mod PCB

Spectrum 48K Composite Video Mod PCB

The above image is the result. This PCB is made the same size as the one inside the modulator so it can replace the original completely. This is quite involved but I believe it to be very worthwhile. Now I have built one up and found Andrew’s mod to work just as it did self-suspending, I have published the design files for the board on a separate page. I did have a conversation with Andrew around the preservation of the original modulator PCBs. Andrew advocated a mod to be done retaining the circuit board inside the modulator, however, I see no issue with removing the internal PCB, so long as it is kept in a state with which it could be re-installed at any time. As long as the original PCB is removed carefully and without undue force, it can be put into storage for such an eventuality. I will leave it to the reader to decide which option suits them.

The first step in fitting this new board into the modulator is to carefully extract the modulator from the Spectrum’s PCB. First I de-soldered both the 5V input and Video Input leads from the Spectrum’s PCB.

Disconnected Video and +5V Leads

Disconnected Video and +5V Leads

Then it was onto the back to de-solder the large tags on either side of the modulator. These can be a little stubborn and, being heatsinked to the body of the modulator, they do drain the soldering iorn’s heat quickly. A good wattage iron and persistence is the key. When I finally freed the modulator, it came away quite easily and I cleaned the holes left on the board in preparation to replace the modulator box later on. Next, carefully solder in your choice of components to the new pcb. You need only choose one option. In this instance I used Option 1 which is Andrew’s Inverted Emitter Follower design.

Modulator Removed and New Board Soldered Up

Modulator Removed and New Board Soldered Up

Next I needed to remove the old pcb from the modulator. This is held in by several solder spots and the two leads coming in through the side of the case. First I de-soldered the solder spots underneath. this requires a freshly cleaned out de-solder pump. With patience, you can get the desolder pump in place and bring the soldering iron carefully in to melt the solder and trigger the de-soldering pump. I took me a few tries but because there is a defined gap between the PCB and the modulator case, it creates a definite separation when the PCB finally becomes free of the box.

De-Soldering the Modulator's PCB

De-Soldering the Modulator’s PCB

You may find that the screen that goes down the center of the PCB is also soldered to the inside of the Modulator. In this case, just de-solder as you have been doing. This particular one was only secured on the PCB but the previous scrap one I had practiced on was soldered on both sides to the inside of the modulator box. Once I had de-soldered the points underneath, I de-soldered the 5V line and the PCB came out with a bit of gentle persuasion. I boxed the old PCB up in a box, labeled it and placed it into my ‘stock’.

Modulator's PCB Removed

Modulator’s PCB Removed

Next on the agenda was to fit the new PCB. I used Blu-Tack once more, to support the board whilst I got it going. I removed it as soon as two opposing points were soldered.

If I had known how difficult hooking up the video socket to the PCB was going to be, I’d have done that first. If you are carrying this mod out, I’d urge you to save yourself 20 minutes of frustration by connecting the video output point on the PCB to the Spectrum’s output socket before you begin to solder the board into place!

I recycled one of the old wires for the video feed and used a new insulated lead for the +5V. Simply maintain enough length for fitting into the Spectrum PCB once the Modulator box is refitted if you are doing this yourself.

New PCB In Place and Connecting Leads Attached.

New PCB In Place and Connecting Leads Attached.

I could now refit the Modulator box to the Spectrum’s PCB. This was pretty straightforward having prepared the tag holes earlier. Once the box was in place, I soldered the flying leads in place too.

Modulator Box In Place and Connections Made

Modulator Box In Place and Connections Made

Now I’d got the Modulator box back in place with all the connections made (The ground being connected via the Modulator case), it was time to test the Composite Output. Unfortunately, as regular readers will know, I haven’t got a large Composite Monitor. However, I have got one of the small 7in models meant for installing in cars. This makes a reasonable test monitor, although would be a little difficult to use for any length of time.

Composite Video Test

Composite Video Test

The image above, shot on my iPhone, shows the board with Composite Output working on the bench. After testing this, I gently pulled the slack cable on the +5V lead into the Modulator box and replaced the Modulator’s cap.

Next, I turned my attention to the cosmetics of the Spectrum’s Case.

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.3 Upper RAM Replacement

As I had assertained earlier, the 48K Rubber Key Spectrum I was refurbishing required it’s Upper RAM to be repaired. Since the chips inside of the machine were old, I elected to replace them with a complete Upper RAM Module. This had the benefit of fitting IC Sockets onto the board if ever I wished to re-fit original ICs in the future.

Preparing for Upper RAM Replacement

Preparing for Upper RAM Replacement

I am really lucky in that I have a ZD-915 De-Soldering Iron at my disposal. I could have used a hand de-soldering pump but the de-soldering iron makes life a lot easier. With both tools, it is essential you take your time and don’t overheat the connections. The tracks on the board are quite delicate and are prone to lifting off of the PCB (as I found in a previous replacement!).

De-Soldering Iron In Action

De-Soldering Iron In Action

As with a hand de-soldering pump, you need to let the solder liquify before triggering the iron’s electric pump. I found it was helpful to make small gentle orbits around the connection whilst the machine sucks away the solder. Don’t scratch the board whilst doing this, only the lightest touch is required. Some joints are really stubborn and I found it easier to leave these until the end so as not to break up the rhythm I’d developed. Once all the other connections have been dealt with, I used my normal soldering iron to add fresh solder to the stubborn joints, giving them plenty of time to heat up and flow through the plated through-holes. I then re-tried the de-soldering iron and they became free of solder without issue.

After de-soldering the connections, I found it was worth going through each of them with a normal soldering iron and pushing the pins into the center of their holes, to fully free them from the sides of the through-holes. This prevents the plating being lifted out with the ICs.

The next step was to very gently lever the ICs out from the board. I found that the ICs were still quite firmly secured and required a moderate force to free them. I did this by using a small screwdriver on the corner of the chip and levering against a part fo the PCB that didn’t have any tracks. If you feel you are putting too much pressure on the connections, you probably are! Go back and see if you can free them any better with a soldering iron in this case. When the chips began to lift, I pushed the screwdriver in further along the base of the IC, making sure not to scratch the board. When you have successfully lifted an IC, check the legs to make sure you haven’t pulled out any plating as well (You may see some solder though)

Upper RAM Chips Removed

Upper RAM Chips Removed

Even though you have checked each IC’s legs for plating, double-check the board for any damage. I managed to remove all the chips on this board without causing any damage at all. Next, I found 8x 16-pin IC Sockets and soldered them in one at a time. I used our old friend, Blu-Tack to assist. My personal technique is to place the IC Socket in the board, checking I have the Pin-1 notch indicator at the correct end. Then affixing some Blu-Tack on the side to prevent it from falling out, I then solder the top left and bottom right connections. After this, the Blu-Tack can be removed and the socket checked for being flush to the PCB. If not, it is a simple case of re-heating the joint required and pushing the socket down whne the solder is molten. Once the socket is completely flush, you can solder the rest of the connections. I also tend to check the connections with a magnifier to make absolutely sure I haven’t bridged them or missed any out.

Upper RAM Sockets Soldered In

Upper RAM Sockets Soldered In

I find a slow, methodical approach to this kind of work pays dividends in less mistakes and good quality workmanship.

The final step was to fit the new Retroleum Upper RAM Module. This is simplicity itself. You just have to line up the top-left pin on the module with the top-left Pin 1 of the Upper RAM IC Sockets and give firm push down. Do this on a nice flat surface. All the instructions for this are included with the module kit.

Upper RAM Module Fitted

Upper RAM Module Fitted

Now, to test the board. For this I used a Bytedelight ZX-HD interface that provides HDMI output from any Spectrum. I feed the signal into a HDMI to VGA Adaptor to use along with my Dell VGA screen.

Testing the Board

Testing the Board

I also stack a Retroleum Smart Card loaded with Brendan Alford’s diagnostic software behind the ZX-HD for testing. Trusting myself to have done a good job so far, I powered up the board and it passed all the tests with no issue. I usually leave the board running for a while in soak to check there are no temperture related problems. In this instance I left it cycling tests for half an hour or so.

Having successfully repaired the RAM, Re-Capped and replaced the regulator, it was time for the next step, the Composite Video Mod.

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Diagnosing 48K Spectrum Upper RAM Faults

By way of a break from the refurb posts; I was recently part of a conversation on FaceBook regardig a coulple of 48K Rubber Key Sinclair Spectrums. Both were proved to have faulty Upper RAM problems by issuing the command ‘CLEAR 65535’. Both machines reported ‘M Ramtop no Good’.

Ian Gledhill, of Mutant Caterpiller fame, was helping Francesco Morandin diagnose the problems. Ian went on to request Francesco issue the commands POKE 50000,85 then PRINT PEEK 50000 and POKE 50000,170 then PRINT PEEK 50000. By comparing the bit patterns expected to those that were reported, the individual ICs at fault could be found.

In this instance, Francesco got 85 for the first test and 186 on the second test for the first machine, then 213 for the first test and 170 for the second test on the second machine. So, working through:

Diagnosis 1

Diagnosis 1

If we then break the values down into binary:

Diagnosis 2

Diagnosis 2

I have underlined the bits that aren’t reporting correctly. After a quick exchange with Ian, I drew up a diagram to show what bits correspond to what ICs in the 48K Spectrum.

IC Position Table with bits

IC Position Table with bits

By finding the IC responsible for the mis-reporting bit, you can assertain whch one requires replacement. So, for the first of Francesco’s machines, IC19 is indicated as being faulty, and the second is IC22.

I have made a PDF of the diagnosis table which can be freely downloaded from HERE.

Co-incedentally, I have a 48K Spectrum with the same problem so I had the chance to use this technique for myself. I did the POKE/PEEK test and recieved 85 for the first test and 171 for the second test. Looking at the binary pattern for 171 (10101011) showed that bit 1 was reporting incorrectly. This indicates that IC15 is the culprit in this case. I have plans for this faulty machine to become a test bed so I’m not repairing it straight away.

A big thanks goes to Ian Gledhill for his insights and Francesco for posting his results.

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.2 Replacing the Regulator

The poor 7805 in any Sinclair Spectrum always works really hard. It was probably the best solution when the machine was designed but things have moved on. Switch-mode technology has improved and reduced in size. Therefore, when refurbishing any Sinclair Spectrum, it’s good to replace the 7805 regulator with a more modern solution.

As I said in the preparation post, there are a few good alternatives now. One is the Murata Switch Mode 5V 1.5A Regulator (They are available HERE), the TRACO TSR 1-2450 1A 5V Regulator or, I have since found out, the TRACO TSR 2-2450 2A 5V Regulator. I have a few of the 1A TRACO units in stock and the Spectrum I’ve refurbished will seldom be used and in my own collection so I decided to fit one of those.

The board was still bare from re-capping but obviously, from scratch, you would extract the board from the Spectrum’s case. Again, pay attention to those membrane ribbons!

Spectrum Heatsink Removed

Spectrum Heatsink Removed

This series documents refurbishing an issue 3b board but re-capping and replacing the regulator will be the same for all of the 16/48K models. In the above image, you can see I removed the heatsink, held on to the 7805 and board by a screw and nut. All thats required is to loosen them and the rest of the removal can be done by hand.

Using a de-older pump, I removed as much solder from the underside of the 7805 connections as possible. It proved to be a little difficult to remove completely and I had to resort to gripping the componet’s tab (the part with the hole!) with a pair of long-nosed pliers and heating the connections in turn to free it completely from the board. The trick is to take your time and not to heat any of the connections for too long. If the pads on the board get too hot, they can separate and lift.

Eventually, I successfully removed the 7805 and checked the pads for damage. All was OK. The TRACO TSR 1-2450 is a ‘drop-in’ replacement but does not require a heatsink. In fact, in use, I haven’t felt it even warm up. I used an old trick to help solder in the new component. A small piece of Blu Tack can be pressed in to service to prevent the component from falling out of the board before it is soldered.

7805 Replaced

7805 Replaced

As you can see, not having a heatsink on the board makes a big impact on the board’s weight and accessability.

TRACO TSR 1-2450 Installed

TRACO TSR 1-2450 Installed

As when I re-capped the board, it would be usual to test the board at this point but since I had already accertained that the upper RAM was faulty and I was going to replace it with a Retroleum Upper RAM module (available from HERE), I decided to leave the testing until after the next stage.

 

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Pt.1 Re-Capping

In my last post, I described the steps I took to prepare for refurbishing a 48K Rubber Keyed Sinclair Spectrum. I am now going to describe how I replaced all the electrolytic capacitors, or Re-Capped the board.

Firstly, I extracted the board from the case by removing the five screws on the undereside of the case. I then carefully flipped the entire case over and carefully removed the top. I did this slowly in order to safely unplug the membrane ribbons. If you open the case to enthusiastically, you can damage the membrane ribbons which will probably result in a replacement being needed. I gently disconnected the ribbons from the board and put the top of the case aside, ribbons upwards. It was then a simple case of removing the single silver screw near the center of the board to lift the board clear of the lower half of the case.

Bare Sinclar Spectrum 48K Board

Bare Sinclar Spectrum 48K Board

The kit of capacitors that comes from Retroleum is very comprehensive. There is at least one capacitor for every one in several models of 48K Spectrum. I have re-capped several boards with the same kit and there’s always spares (into my stock they go!).

My technique for replacing the capacitors is to use a hand de-solder pump and to work methodically across the board, doing one capacitor at a time. This gives you time to check and double check which way around the components fit and to make sure you get the correct value from the capacitor kit.

Methodical De-Soldering

Methodical De-Soldering

Check out my ancient Weller TCP-FE soldering iron, still working fine after over 30 years of use! It’s never failed me.

I extracted each capacitor carefully, so as not to damage the traces on the board. These can be damaged easily so I only heated joints when necessary and tried to remove component leads gently. Easier said than done with stubborn leads but patience is king here. If necessary, balance the board on it’s edge, hold the component lead from the top side of the board with a pair of long nose pliers and heat the joint from below the board. Go slowly and pull gently. Only pull the component lead when the joint is adequatly heated otherwise the component will be released too fast. If your de-soldering pump is doing it’s job properly, this should seldom be required.

Soldering In the New Component

Soldering In the New Component

One thing I am a stickler for is neatness in my work. Neat work is good work and makes things easier later on. To this end I bent the components leads at right angles with the help of long nose pliers, a little distance away from the components body. I roughly measured the first couple I did to get an idea of where exactly to bend them. Bending the leads away from the components body affords some strain relief when the component expands and contracts with temperature. Another thing I make sure of is to make sure the components labels are facing upwards. This is not only neat but would help later if any required replacement. Once soldered. I clipped each lead by holding the free end and clipping close to the board. By holding the leads when you do this, it avoids them flying out of control and avoiding potential eye hazards. I have a large coffee tin where I put these off-cuts because they come in very useful for short links and other tasks.

Freshly Re-Capped Spectrum

Freshly Re-Capped Spectrum

When you have completed the re-capping, examine all of the joints even if you have been checking them as you go. It is really easy to miss a’dry’ joint and is difficult to find later. If you see any joints you are not happy with, simply reflow the solder and add some fresh for a good joint.

When finished, I would usually test the board but I was confident I’d done a good job and I was going to move striaght on to replacing the power regulator next in any case. I will describe that process in the next part of this series.

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Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum – Preparation

Recently, I was lucky enough to ‘win’ a pair of 48K Sinclair Spectrums. The original rubber keyed variety. This model was one of the first I ever owned (the actual first being a Sinclair ZX81).

Rubber Key Sinclair ZX Spectrums

Rubber Key Sinclair ZX Spectrums

Here, I have managed to obtain issue 3 and an issue 3b models. The one with the better case is the 3b so I chose that to refurb first. In preparation for this, I tested both machines. I was surprised to find they both worked, at least to the copyright message, and both the membranes were intact. In fact, the issue 3b seems to have an aftermarket replacement membrane.

The one thing I did notice is the speed at which they both got to the copyright message, it was very fast, a telltale sign of upper RAM issues. This was confirmed when I put a Retroleum Smart Card on the back configured with Brendan Alford’s diagnostic software. Retroleum also supplies diagnostic software with their card but I have grown used to Brandan’s so I use that.

The test revealed that several of the upper RAM ICs on the Spectrum were not reading back correctly. Rather than replace the individual chips which are not the easiest to find, I decided to use a Retroleum Upper RAM module instead. This replaces all the upper RAM with a single module, relieving the old machine of lots of it’s legacy ICs.

Another vital thing to do is a re-cap. The capacitors in old machines often fail and in the Sinclair ZX Spectrum, can lead to faults in other parts of the machine. Again, Retroleum to the rescue! They do a complete re-capping kit that includes a Composite Mod too (although in this instance I will be using my own composite mod solution).

Further to the above, I want to replace the inefficient 7805 5V Regulator. There are two easy solutions; one is the Murata Switch Mode 5V Regulator that can supply 1.5A of power (also available from Retroleum), or the smaller TRACO TSR 1-2450. Since this machine will be seldom used and part of my personal collection, I decided on a TRACO unit.

The last thing to consider is the general look of the machine. The issue 3b’s case is in good condition with only one missing foot. One thing that is dissapointing is the state of the front fascia. It has several dents and a few small scratches. Luckily, all these spares are available nowadays and I chose ZX-Renew to supply a new black fascia.

Sinclair ZX Spectrum - Showing Dents

Sinclair ZX Spectrum – Showing Dents

Once all these spares have arrived, I will post updates in parts to show each step in the process that I take.

Series Index: Refurbishing a 48K Rubber Keyed Sinclair ZX Spectrum

 

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TZXDuino Compact v1.01 and other projects

The TZXDuino Compact v1.01 PCBs arrived today from Hackvana.com I have built one and tested it successfully, so the design files are on the AVR Projects page. Feel free to use the Gerbers with your favourite fabricator (Hackvana are good!). Alternatively, you might like to modify the design to suit your own requirements so I have included the KiCad files and a schematic along with the latest (v1.7b at the time of publishing) arduino code.

TZXDuino Compact v1.01 In Action

TZXDuino Compact v1.01 In Action

For some TZX/TAP files, the output seems a little weak but in conversation with Duncan Edwards, one of the designers of the original device, he told me that later Spectrums do suffer from a less sensitive input. I will look into updating the design with a small amplifier to alleviate this issue. It has also come to my attention that I’m using the wrong display. The code specifies a 128×32 OLED and I have used a 128×64 OLED version. All this does is stretch the characters though so it’s OK to do so. The connections are the same. Admittedly, it does look slightly better in smaller text but the display is rotated 90 degrees. Choose which one you feel works best for your application.

Meanwhile, the composite mod suggested by Andrew Gostling wouldn’t drive the Dell UltraSharp 2007FP monitor. It seems that this particular monitor is really picky with it’s input signal. It also fails to work with my ZX Uno. I have since started using an alternative Dell E173FPf monitor along with a ZX-HD interface, driving a HDMI to VGA adaptor. The ‘2007FP will be pressed into service elsewhere!

I have a few other Spectrum related projects on the go. I have formalised Andrew Gostlings Composite Mod along with two other popular options and designed a PCB to replace the original 48K/128K/+2 modulator internals.

Spectrum 48K Video Mod

Spectrum 48K Video Mod

This I have yet to prove, but once I have had PCBs made and tested them I’ll be publishing the design files on here under Non-AVR Projects.

Another Spectrum related project is a Floppy Drive adaptor board for the Spectrum +3 It is meant to give the facility of easily making a connection cable up from an old PC style floppy cable and giving the facilites of both setting the drive as Drive A or B and also using Side 1 or 2. I have had no end of trouble with this one and development continues.

Yet a another project is an NMI interface, initially for 48K Spectrums. This will hopefully allow interruption of  any program running on the Spectrum and an alternative ROM to be paged in, similar to the Multiface except you can use a custom ROM. I’m hoping to be able to run the Multiface machine code monitor Genie and maybe the Specmate snapshot devices ROM Code.

 

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