Posts by jlopez


    I repaired one recently. In my case it was dead Z80 - unfortunately not yours. Still, I think if you still don't have the technical manuals I found them there.

    If it fades after some time I bet the culprit should be a capacitor.


    Well, don't worry. I could play with what I had and made a rearrangement of the pages from both files. I think they are correct now, but without the paperback source I can't guarantee either if any page is missing or the order is maintained.

    Thank you very much

    P.S. I append the ammended files. I hope they are useful.

    Die Scan Arbeit wurde nicht von mir, sondern von Klaus Kämpf (auch hier im Forum) durchgeführt. Ich war lediglich beim Transport beteiligt.

    mfg. Klaus Lo,

    Hello klaly,

    I have examined the documents... I'm not sure but in my opinion there has been something wrong during the scanning of the CPU cards' manuals.

    * CAAA02 has 22 pages while CAAA06 has 11

    * CAAA06 has pages 1-4 (3-6 in the pdf) repeated at the end of the document

    * CAAA06 contains only a schematics page (USART)

    * CAAA02 contains 8 pages with schematics, including those of CAAA06

    * CAAA02 has page 1 (page 13 at the pdf) duplicated at page 14 of the document

    My guess is that both documents got mixed. I don't know Mr. Kämpf's alias so I cannot ask him if a revision of those documents could be done. Could you get in touch with him, please?

    Thank you and regards,


    Thank you netmercer  klaly  horniger  Holger  jobi23  Raffzahn for your involvement in taking care of this knowledge. For years we could only rely in helwie44 documents and a few scraps we have been able to obtain by other users' findings and reverse engineering. If I could ask you make it public when the work is done I would be very grateful.

    Also thank you helwie44 for getting in touch, otherwise I would have missed the documents for sure.

    Now that the communication between expanded memory and CPU is clear, I might be able to end my memory expansion. What I could not find is when do the video card discern whether the bank is activated or not.

    Cool! Damit ist aber auch klar, dass ich mit meiner "Standard CPU Karte" und 16 KB SRAM Karte keinen Erfolg haben werde.

    Ist ja insgesamt kein Problem, ich habe ohnehin noch zwei P3 mit 64 KB (und diverse PCs mit 4 bzw. 8 GB) ;)

    Well, now that many technical manuals are known not to be lost you may have a chance. What backplane and CPU card do you have?

    No need to thank. In reality, I should thank you. I tried to map it two or three times, but my head is not where it should be. At least for me its a relief you find it useful. You may need the component layout too to trace it correctly, tomorrow I'll scan it.

    Don't worry. Tomorrow I'll prepare some crash course for you.

    First, you need to clone the repo. This means creating a local copy of it into your computer.

    The easiest way is by selecting "Code>Open With gitHub Desktop"

    Then a folder structure will be created on your hard drive. Github Desktop will take account of the changes you make and, when you are sure the contributions you made are fine enough then using GitHub Desktop you shall proceed to commit and push.

    Summary is mandatory, description is recommendable. After that you may see push on that same screen; that would add the changes into the repository.


    Repository created.

    SKS-Alphatronic-DS Archive

    It actually contains some of the datasheets related to the main ICs of the computer, the Spanish Char ROM and the scans for CAAA08. I suppose I could add more data yet today it's not the best to dig into my hard drive. Still, it is accessible for in case anybody wants to add/modify anything.

    Best regards

    If structured correctly we could store all related datasheets, lists of compatible references for the main ICs, manuals, system ROMs, schematics (with US logic nomenclature), kicad symbols and footprints for obsolete parts.

    Well, by small I meant we aren't like the Commodore or Spectrum user groups and as such we must rely more on ourselves.

    I suggested GIT because it provides a high degree of reliability regarding the members and how they manage the project. In case of the foresaid board, I retraced around half the tracks but every time I tried to continue I lost focus and had to stop. While github is mostly software-oriented, there are also hardware projects dwelling around.

    Don't worry about that. I could teach you how to do it, but only if you are ok whith it ;)

    I was wondering if it's possible to change the banking from MOS with some command. Checked the manual but was not able to figure out if it's possible to send an OUT to the CPU to modify the banking mode. Do you know if this is possible?

    It's a pity that the schematics are no longer available. :cry2:

    It would be out 0x78, 0x20 // out 0x78,0x60; you could trigger it using the system hex monitor. However, if the test program is not well-written you may lose MOS control and become stuck in the extended bank until reset.

    Yeah, that's sad; but let's not cry over spilled milk, do we? After all it is how war is, and time is an unforgiving enemy. Fortunately, even if we (P2/P3 users) are a small community inside this generation of computers' curators we may succed in preserveng them with the help of one or another. Fortunately helwie44 has been able to save most of the software related documents, so the soul of the system is mostly safe.

    Returning to more practical matters, I could post the scans here or alternatively I could upload them to a new git repository so anybody interested could work on it. What do you prefer?


    - There is a connection in the backplane between the 48K and the 16K boards. My theory is that it allows to disable PCS from the 16K card. This makes probably sense because the output buffers of the 16K board are always active (the 74LS240 has the output enable line to GND) and therefore there must be a way to avoid both output buffers in both cards to be enabled at once. This is performed by the backplane connection on pin 75 or at least this is what I have observed in my setup.

    I found the scan of the paper I made long ago regarding CAAC08. Sorry, it's not the cleanest but I hope it gives some insight of how this works.

    In case you need schematics for the CPU board, I don't have them but I have the next best thing: the scans of the bare, unpopulated board on which to perform the reverse-engineering process. Reference is CAAA08 (P3) so there may be some differences such as a single 4k ROM, etc.

    overCLK : Could you monitor the states of both /RD and /WR at the same time while testing?

    According to the docs, /PCS is used to inform the controller that a request was made, initiating the proper cycle. Assuming /PCS is low, cases are as follows:

    LowLowTest cycle
    LowHighRead cycle
    HighLowWrite cycle
    HighHighNo Request

    If you monitor both control signals directly on its corresponding pins of the DRAM controller and found them stuck at a wrong state it would trigger a test cycle instead of a read/write one. If that was the case, you would only need to trace the signals back into the backplane and check what components modify their state.

    By the way...

    My Italian card is not the same as neither yours or helwie44, but my P3 DRAM board is CAAC09 which has connections in the 3rd slot. Both wear a 8202A.

    I could test with mine if you want.


    I took a look into the 8203 datasheet and found this interesting excerp:

    16k/64 Option Selection

    Pin 35 is a strap input that controls the two 8203 modes. Figure 4 shows the four pins that are multiplexed. In 16k mode (pin 35 tied to Vcc or left open), the 8203 has two Bank Select inputs to select one of four #RAS outputs. In this mode, the 8203 is exactly compatible with the Intel 8202A Dynamic RAM Controller. In 64K mode (pin 35 tied to GND), there is only one bank select input (pin 26) to select the two #RAS outputs. More than two banks of 64K dynamic RAMs can be used with external logic.

    In other words, if pin 35 is not grounded it should behave as a 8202. So, it's the same as with the video card using 5027 or 5037.

    Maybe they got short of 8202 and started using the then new 8203. I'm going to check what the Italian had installed.

    Meine Karte ist mit 8 x Mitsubishi M5K 4164 NP-20, also 64K dyn. RAM bestückt. Der Speichercontroller ist ein Intel D8203 und kein D8202, so wie bei der 48K Karte. Meine 64K Karte wurde vermutlich auch baugleich in der P3 verwendet.

    Ich fürchte, daß ich Euch daher nicht viel weiterhelfen kann :(

    Don't let you down so easily, sir.

    Intel 8203 has more modes than 8202 but according to the pinouts they don't seem to be that incompatible.

    If not using the new modes, I imagine it could be even considered as a compatible replacement.

    The P3 is more or less a P2 - les ROM, more RAM and also more cohesion between systems. many boards are identical for boths systems and bank switching mechanics are the same. My bet would be studying the P3 16k expansion boards: if the memories are managed from the other board, the rest of the logic should be bank-related,



    Sorry, I am late

    • I also had issues with a P3, which suddenly stopped working (it did not boot anymore and just showed the flashing "RESET" message). Here we also suspected some RAM-related issues and tried to understand the RAM addressing logic. We investigated the switching from 48K+ROM mode into 64K RAM mode and tried to understand differences between P2-48K, P2-64K and P3-64K configurations. Unfortunately we did not complete these analysis successfully, hence these experiments do not provide additional insights into the issue of @overCLK's P2.
    • Generic findings on memory boards for P2: I have one P2 with a 48K memory board and a second P2 with 3*16K memory boards. Hence I can confirm that the 16K boards work independently from 48K boards. However as mentioned above, I don't know if this is also true for the P2-64K setup. Usually there is this "adapter board" that is attached to the 48K board, allowing to "shift" the addressing (see Maybe in you case, this adapter board is now broken and you can try just the 48K RAM board in the machine (without adapter and extra 16K board).

    In case for the P3, that's not always true. In my case my P3's 48K board and the 16k share signals through slot C. I don't have the documents I made right now but I recall the data bus to the memories to be dependent from the memories at the 48k board.

    About the switching mechanism... A few months ago I build the entire 1MB sram board on breadboard and attached it into the backplane. To switch I used signal #mosen on the backplane (slot A or B?). Unfortunately it did not work and I'm still in doubt if it was poor wiring or the use of the wrong signal.


    Amazing story! :D

    I noticed the quotation has a line your post don't show... curious.

    No, I don't have a plan to read the memory. I bought it for static display althought I was fully aware that the content is non-volatile, unless read (this kind of memory has destructive read, right?). So bad I don't even know the word size for it... The matrix is 128-bit but I don't know if it is 16 cells x 8-bit or 8 cells x16-bit.:nixwiss: The required voltages are written on the board, so I imagine I could power it. Sounds funny but I have an overhead of months and will have to wait.


    I got my first rope memory!

    Unfortunately I haven't found any background information about the computer itself other than its name "Wagner WAG.40"...

    I also received another core memory board, which is more compact and with more capacity, but is less interesting to see without some magnifying lens.



    As soon as the board arrives and I have some time, I'll report what I find.

    Two days ago the board arrived as expected and, when I had some time just before lunch I made some tests.

    (Top board, my Italian video system; Bottom board, Shiri 's Spanish video card)

    First I checked (again) if there was no shortcircuit in any of the power supply lines. There was no problem.

    I plugged the board at slor nº4 of the Italian unit and turned the system on, being greeted with the RESET message. So, with the new VTAC the board works, and so does with the second VTAC of the lot he bought. Then I proceeded to test the original 5027 only to find it is not broken. Both facts come as a relief as I was expecting a worst-case scenario. Still, even being great news they are confusing.


    The video card works as expected. No VRAM or EPROM fault.

    The monitor was tested with a game console and found to be working.

    His CPU initialized correctly the VTAC on both cases he tested it, judging by the cursor images he shared. So system ROMs seem to be fine.

    Other than the power supply hack (which may prove to be unstable), could the wiring between computer and monitor be the cause of such distortion? Any other board interfering someway?




    The board is in transit and may arrive as soon as tomorrow. Meanwhile I have checked again the SKS schematics. From the description and pictures, and if there isn't another problem with power supply (such as failing -12V on Shiri 's side or broken zener) I have reduced the options to four possible causes, involving up to eight components:

    A) VRAM failure (D5, D6, E5, E6). If the memory was wrong and somehow it always outputs 80h the result would be a screen as the one shown. Still, I thing such a case is so remote that I'm sarting to rule it out.

    B) 74LS175 failure (B4, B5). If the memories were fine but the EPROM doesn't receive a correct value, culprits would be this pair.

    C) 74LS166 shift register failure (B6). If its output maintains a high or undefined value (not low) next component that feeds its inputs with this signal may pull it up and generate an inverted blank screen.

    D) TMS2716 failure (A6). This is the worst possible case to be expected and also the most probable of all scenarios. Was the EPROM the cause, its data output could go high or undefined, making the shift inputs to pull them high internally and generating the inverted blank screen.

    As soon as the board arrives and I have some time, I'll report what I find.



    Hello helwie44,

    After the replacement, image seems stable, at least from what I've seen. It is a perfect blank, but inverted screen.

    Picture courtesy of Shiri

    The replacement is a legit VTAC, otherwise we wouldn't see the cursor (or anything at all). This seems a fault from the video RAM, latches or maybe some other common component coming before the shift register because (as seen on SKS documents and later with the EPROM backups) MSB is the invert signal. As you said, the TA board is a modified SKS but this remains unchanged.

    Yes, Shiri is a bit far, but even if he was near I couldn't meet him due to restrictions on mobility... Still, he sent me the board through mail. When it arrives, I'll give it priority over the PETs.

    Kind regards,



    It's been some time. Last week the VTACs arrived and the one in the card was replaced by one of the Polish units. The image was stable, cursor moved but there was no character at all! The invert signal was also activated, so the screen was green with the exception of the cursor... This means, that the data path from the DIN to the VRAM and from the VRAM to the shift register should be checked. Being completely blank with the invert I imagine:

    A) some 2114 may be faulty.

    B) some 74 series IC in the bus may be faulty.

    He has no scope to check the signals in the card... so he was stuck with it. For this reason, we agreed I would be in charge of the board for some time as I received one of such instruments not long ago. I don't expect it to be a long repair: as the VTAC retains most responsiblity for the generation of the signals, it shouldn't be as complex as a non-6545 PET.




    I have some new things and others that aren't that fresh but also worthy to report.

    With this I regain the ability to repair hardware!

    I found one of the rare tax-evading Amstrad computer!

    I found many interesting things in dump piles near my home, including this ATMega, four breadboards, and some videoconsole boxes.

    My father brought me some astronaut backpack!

    Last, but not least, Toshi sent me the original monitor for the P2. This way, my Italian unit is complete. He was generous and never asked a price! So thank you very much.




    A few months ago I was delighted when I learned the Deutsch word "Hamsterkauf".:hamster:

    It is my turn to expose a word from the country where I was born: "Estraperlo".


    "Estraperlo" comes from the name of an electrical roulette made by two Dutch men called Strauss and Perlowitz. Albeit gambling was forbidden during the Second Spanish Republic, top public officials gave permission to them to operate. This corruption scandal was soon discovered and as most officials in the government were involved (including prominent members as the PM Lerroux and the mayor of Barcelona) prompted the third and last elections of the period, literally destroying the center-right parties and polarizing the country which went into a crude civil war not long after. When the war was over the word was associated with the black market and, after the postwar famine, with anything related to corruption, illegalities, black markets, etc.:capone:

    You may be asking yourself: "Fine, but why is this guy talking about this in an old computers forums?". Well, to be fair, this is the Amstrad forums, I'm talking about Spain and also about something wrong (maybe even illegal) that shouldn't have ever happened. Knowing those facts, you may be already guessing what's going next.8o

    The responsibles of this lied both to the authorities and to their users because they didn't want to pay some taxes... Spanish picaresque at its finest. It is not clear if it was Amstrad itself who gave the order or was the filial company in Spain who did it. Nevertheless, they never got caught. This is the second model, so "Ñ" key and standard BASIC 1.0 ROM (464)... was the older model it would have British keyboard and BASIC 1.1 (664).

    I imagine that as it can only be found in Spain it may be rare to see this piece of hardware around this forums, so I thought you may be interested in seeing it.;)



    Hello Helmut,

    That's a relief. I told him the failure was most likely caused by the VTAC, but I wasn't completely sure. If that's the cause, the computer may be working very soon.

    I haven't only guided him to find what was preventing the computer to start, but I supplied him my remaining ATX adapter and 48K replacement kits.

    gpospi I was writing this when you replied. Thank you! ;)