It has been known for a number of years that the original motherboards have been failing for a long time and in dire need of servicing and modifications to keep them running. The total time and expense of undertaking all this work is really where the remake boards come into play. Not only do you get a fully updated board with all known tweaks and fixes, they have many new features built on as standard which saves you the cost of buying and fitting many upgrades later on.

The remake boards are a lot more than just a simple clone of the original ST. They are a amalgamation of the best bits of various ST designs mixed in with years of experience and knowledge making a completely new motherboard. They are designed to be a drop-in replacement for existing STF/M machines and with its generous I/O capability, it makes a solid foundation for the development of future add-ons.

The motherboard uses a quality 4 layer PCB and has been designed with the intention of being long-term reliable. It's easy expansion means newly produced add-ons are simply plug and play. No need to ship your machine halfway around the world to upgrade it with all the time and expense involved! No more costly mistakes when you bodged the install yourself and end up having to pay someone to fix it all for you!

Rest assured that these motherboards all have every legacy connector. You can still use the cartridge port and MIDI connections and your existing DMA devices etc. All remake boards remain 100% backwards compatible to existing STs.



RAM failure and upgrading is one of the most problematical issues on ST's.

On a typical motherboard there are 16 DRAM chips which make up a measly 512K of RAM. Populating the empty bank takes you up to 1 MB.Upgrading further to 4MB gets even more complicated where adapter PCBs and wires are often needed to upgrade. Though often dodgy connections cause problematical debugging, especially when the user does not have the technical ability or necessary equipment to diagnose the issue. often the machine will have to be sent off to a experienced engineer which can be time-consuming and costly.

The H4 does away with all these problems by using a standard 72 pin 4MB simm.these are plentiful and normally a order of magnitude cheaper to purchase than existing memory upgrade solutions. Such memory is extremely easy to install, and should at any time one of the RAM chips fail, the simm can be quickly replaced in a matter of seconds at no cost other than a replacement simm.

Current versions of the H4 & H5 motherboards also include header pins to plug in a existing 4 MB Falcon RAM board. such port is also extremely useful for developers or people who need to plug in various boards for testing different DRAM on.



The STs all had separate red green blue driver transistors which served as a digital to analog converter via a resistor ladder.It certainly did the job, but it used a lot of components, was prone to noise, and there are certainly better solutions out there today.

The H4 & H5 series all use a dedicated video DAC chip which is the same one as used on the Falcon. This gives a much sharper and colour accurate image than resistor ladder designs.

The added bonus of the new video circuit, is we integrated a RGB / MONO switch which drives a standard VGA connector. People are probably familiar with various "ST2VGA" adapters etc. The remake boards have this built on as standard. This saves you having to purchase a third-party product. The motherboard itself has a option for the standard ST DIN RGB connector, or a standard VGA connector.

A lot of components around the shifter area were relating to the 32MHz generator. It was never particularly great, and there are much better solutions now, like a dedicated 32MHz oscillator which is fitted to the remake board as standard.



ROM is yet another problematical area as there are so many different layouts and types of ROM, it makes it all a bit of a minefield.

Some early STs had six ROMs which was generally TOS1.00 or TOS1.02. because they will early versions of the operating system, using a later versions such as TOS 1.04 is really a must these days. While upgrading 6 chip TOS is generally easier than 2 chip, there is basically no easy alternatives to simply upgrading 2 chip TOS to TOS1.04. There are of course various kits and adapters which can convert more modern chips to fit, but like with everything else, if you cannot do this job yourself, you have to send your machine away to someone who can fit it for you. This again, can end up being expensive for a otherwise simple task.

On the H4 & H5 series we opted for a standard 16bit PLCC ROM. the ROM is actually big enough to hold two versions of TOS which is currently selectable via a simple jumper link on the motherboard. Then you can simply program which are the variations you want and plug it in. Generally you can have TOS1.04 & TOS206 (with a suitable decoder board) or simply TOS1.04 and EMUTOS if you prefer. ROMs are inexpensive and easy to program, so again ,a huge time and cost saver.



The old "Mars bar" type CPU has been replaced by a more modern low-power PLCC CPU. these are a lot easier to obtain, and fitting removal is generally easier then the DIP types. The PLCC HC CPUs are also capable of running up to 32 MHz with a suitable booster.



A lot of people do not realise that ST motherboards have a -12 V generator circuit with the TL497 PWM controller which is required for RS232 circuit is to function. There are also two accompanying chips which are typically the 1488, and the 1489 RS232 driver chips. These involve a fair amount of components and board space which we wanted to reduce. So we opted for the more modern MAX238 IC as it has a fully integrated RS232 driver with a on-board negative voltage generator which only requires 4 low-cost external capacitors to function.

A few logic chips have been removed and their operation optimised. For example, there was typically two inverters in series as inverters generally have the best output currents. However this required two inverters in a device when it could use a more modern single noninverting buffer instead. So all the "double inversions" were removed for single higher current buffer chips and there has been various other logic optimisations around the motherboard as well.

The RF modulator circuit has been totally removed as TV sets generally do not even have a input for this any more. this by itself has saved a fair amount of board space and components.



DMA related issues have plauged the ST design since the very beginning. On the STE there are buffers which presumably were there to help eradicate such issues, but in reality these basically did nothing to help. One of the major faults was just down to bad grounding & layout on the motherboard itself. All the usual cost-cutting measures such as omitting pullups on the data bus further caused problems. More recently I have found another bug where the floppy controller tolerances itself can cause the floppy drive or hard drive to malfunction. The amount of problems just relating to that one circuit is almost insurmountable and I have already documented it in great lengths.

All the knowledge and experience I have gained over the years have been put into practice on the H4 and H5 series motherboards. All known DMA hard drive and floppy related issues have been solved and integrated into the remake boards design as standard.There are certainly no problems whatsoever in using the -38 DMA chip or the IMP branded DMA chips on the remake boards.

As a added bonus, I have integrated my automatic high density floppy control circuit and media change fix support. Which is all integrated into a single low cost GAL. Upgrading original machines with a floppy kit can be time-consuming and expensive, such features are just simply built into the remake board as standard.

It is also no longer a requirement to alter the drive select ID of the floppy drive is used, you can simply plug in a existing PC floppy drive without modification.



The original ST reset circuits were generally using the NE556 or NE555 type timer chips. while these offered a cheap solution, they still used a fair amount of components which were prone to failure. In particular were the electrolytic capacitors which cause no end of reset related issues which seem more prominent on the later STE / Falcon machines for some reason.

On the remake boards went for a all integrated dedicated reset chip which only requires a simple resistor and no electrolytic's or capacitors whatsoever. This gives a much sharper and reliable reset signal to the entire motherboard. the reset switch on the motherboard's works exactly as before and is used as a auxiliary reset input to the chip so no functionality is lost.



One of the most annoying things about the whole ST range is just simply lack of expansion options. Expanding the machine generally starts with removing the CPU and placing it into whatever upgrade board is being fitted. As usual inexperienced people have to send their machine off someone who is capable of undertaking the work which again is all time and expense. Some people who attended themselves often end with a broken machine where they have to send it off to be repaired which is time and expense again.

On the H4 boards there are 5x 68K sockets for easy upgrades which is often as easy as just plugging it in! The H5 has 4x 5V 68K expansion sockets, and 2x 3.3V expansion sockets for future developments.

There are also two internal DMA ports. A classic DMA port such as used on the mega ST, and a second one which can be used for a internal ultrasatan.



The H5 series has a new 3.3V bus. With 5Volt devices and I/O buffers contributing to one of the largest expenses in upgrades, we decided to include the I/O buffers on the motherboard itself rather than on individual add-on boards. This means expansions can use solely 3.3 V devices which are lower cost than 5volt devices and considerably lowers the amount of chips used.

We are already working on designs which use this bus such as "flashy clock". while we will produce a 5Volt version for original machines and the H4 series boards, these upgrades will be considerably more expensive than the 3.3 V versions.



One of the most annoying things about the ST range is the funky PLCC sockets. There are no easy to find sources of these funky sockets. So if you needed to replace one, or just wanted to simply install a blitter, you would have to build a adapter board or find a used socket. On all remake boards we just simply use standard easy to obtain 3M PLCC sockets.



Electrolytic free design! No more re-capping years down the road! Finding replacements is a daunting task by self, never mind the time and cost involved in actually replacing them all. On the remake boards we totally did away with all the electrolytic's and only use ceramic capacitors which will never dry up over time. Ceramics offer much better performance with faster transient response times and help keep a clean supply rail across the entire motherboard.



Another annoying aspect of the ST is the soldered on floppy cable. So the cable become damaged it is difficult to replace and often you have to salvage one from a scrap ST. It is also annoying if you need a longer cable as you cannot simply plug in a longer one.

On the H4 & H4 boards resolve this problem by just adding a standard floppy connector as standard. You can use a generic PC floppy cable or even make your own to whichever length you desire.



The H4 & H5 series all have a built on "Forget Me Clock II" Real Time Clock as a optional extra. Simply plug in a DS1315 RTC chip and you can enjoy a Y2K compliant RTC battery backed clock using the FMCII software.



The legacy cartridge port as a sinister secret...

Almost everything which plugs into the cartridge port ends up having a software hack because of the missing read/write signal, but not any more! The H4 & H5 series repurposed one of the ground connections into a tri-state buffer which feeds the CPU R/W line to it instead. Due to its clever design, legacy cartridges can still be used and it does not damage the R/W signal if the cartridges short out that pin to GND.



Yes my friends, the constant confusion over swapping drive A and drive B, internal and external drives, can now simply be done by a simple set of jumper links on the motherboard. No more track cutting or any ugly hacks, we have it covered!





Are these assembled ?

The H4 series was bare PCB only. The H5 series is with "bird seed" meaning all generic SMT resistors and capacitors are pre-assembled along with some basic SMT IC's . Later runs had more fitted such as the sockets and the DAC IC etc. Some basic assembly is still required.

In the future there may well be fully assembled and tested boards, but these will not include the main chipset which you will need to obtain from a donor machine or elsewhere such as the exxos store


Can I get one fully assembled ?

There have been a few people on the forum who have offered to build them but currently they are not available fully assembled from exxos.

People have to bear in mind that these things take a serious amount of time to do plus the price of the parts. Originally the bare motherboard ended up costing around £60. There was around £100 of generic "birdseed" parts alone. Plus paying someone to assemble the board even at that point would easily cost £100. These are large four layer boards which are not cheap to produce and are extremely heavy to ship about with all the parts on also.I was really pushed to keep the price of the board currently sold under the £150 mark. Some people have already complained about the expense of the board but in actual fact it is extremely cheap for what it is already.

The problem with finishing off the assembly is there could easily be £50 in various sockets. It generally costs around £100 to obtain a scrap machine for parts. Plus a days work in dismantling and desoldering and testing the chips which can easily add £100 of work. Plus then the fitting of parts and all the time involved with testing can easily be another £100 for a days work. Realistically would add something around £400 to "finish off" the board. Plus the cost of the motherboard itself you are looking at a round £550 worth of kit.

This is all ultimately why the motherboards were only built to a point to make things as easy and cheap as possible for the end user to finish off the assembly and obtain parts themselves. Shipping also becomes incredibly expensive for a complete machine. It was a monumental effort to keep the price of the shipping down as cheap as possible just for the barebones motherboard.

Ultimately experience has shown that people always want things doing but rarely want to pay the going rate for anything near for all the work which is involved. So I hope people realise the problem I am faced with with selling complete machines or at the very least built and tested motherboards. I mean sure, if you want to throw £100's my way and prepared to wait several months then yes they could be done. But realistically I do not think there are many purists who want the best machine who are actually willing to pay for it.


Do I need a donor machine ?

Basically yes. We do not recommend sacrificing a working machine for parts though. These boards are intended to be replacements for the many machines which have failed and where the main chipset and sockets can be reused on the H4 / H5 platforms. Alternatively there are a range of parts available in the exxos store.


Can you add this or that wizz bang idea upgrade ?

While we have plans to build on some upgrades as standard in future boards, a lot of these upgrades are still in development and will be available as simple plug-in options later on. Everybody has their own ideas for upgrades, but please note, if you want a particular upgrade you also have to bear in mind that such upgrades often will require software & drivers which people are not normally willing to invest time in. The remake platform is to make a reliable and easy machine to upgrade and please note, we cannot design and build everything under the sun, it is down to the community to develop various add-ons for it.

We do however have a lot of upgrades in the making which will be compatible, such as accelerators, ram expansions, IDE, flash ROM etc all these upgrades will simply be plug and play.


Are these boards compatible with existing upgrades ?

Yes.. and no.. while it can of course use any upgrade which would ordinarily work in a standard ST, we are driving this platform with new upgrades specifically designed for this motherboard. As such older upgrades may well conflict and not function correctly. with so many old upgrades out there impossible to counter for them all, in particular, a lot of these or old upgrades are in short supply and it is just not worth the hassle in trying to make them compatible with everything else.

As such, we do not recommend using older hardware upgrades with this platform. All designed and compatible H4/H5 upgades will be labelled accordingly.


What OS can I use ?

Like with the original ST, your limited " out of the box" to TOS 1.04 or 192K version of EMUTOS etc. You can however use TOS206 with a suitable decoder board which are available from the exxos store. there will be more advanced flash ROM options such as flashy clock where you can simply flash whatever OS you want to run very quickly and easily.

It is also worth noting that with small bugs in TOS206 running with a 030 based accelerator, such as the terrible fire TF536, it requires a patched TOS206 will be available in due time. We also plan to build upon TOS206 to include more built in features and control over the H4/H5 hardware addons. We hope to reduce the amount of auto folder programs which will be required for hardware add-ons and just build in the relevant routines into TOS directly .Alas, the Phoenix OS will be born :)


What is the difference between the Alpha / H4 / H5 / Phoenix / legacy motherboards ?

The alpha was the original " will it work" type motherboard. We don't talk about that one :) The H4 as described in all the sections above, is a hugely updated motherboard which almost all based on through-hole components to allow users to easy assemble them. The H5 is the next alliteration of the board which includes a new 3.3V IO bus and has a lot of the tedious components such as resistors and capacitors changed over to surface mount and assembled at the factory. These motherboards are generally aimed at developers.

The Phoenix motherboard will basically be the final product and we are starting to use that name as opposed to motherboard revision numbers such as H4 / H5 etc. The Phoenix platform will be truly born once we have the Phoenix OS in operation and we can start considering small production runs of complete boards.

The legacy motherboard is basically a compact version of the H4. With the rise in postage costs and the failure rate of original motherboards ever-increasing, we wanted to produce a low-cost as possible replacement motherboard. Read more about it HERE .


Why do a new motherboard and reuse old chips when they can be done in FPGA?

The simple reason that we want to keep the original machine spirit alive. There are already multiple platforms out there with " system on chip" such as MiST, FireBEE etc etc there is no need to reinvent these projects. What we want to do is have a easily upgradable and bug free replacement STF type motherboards. It is also worth noting that a lot of the FPGA cores are still not 100% accurate to the original chipsets. So there will always be some compatibility lost.

We are however constantly investigating replacing the original chipset with FPGA simply due to the fact we need to do this in order to expand on the features and functionality of the original chips. if people want a genuine legacy system using original chips, then they can invest in the legacy platform. Those who are wanting to move slightly away from compatibility and go with machines with more features or faster speeds etc, they can invest in that platform once it becomes available.



Last updated March 9, 2023 10:20 AM