Posts by overCLK

    Actually there is only a reset circuit (reset-in to the CPU). The problem is that different boards make different "contributions" to it, changing the characteristics of the RC net. I guess that with the original power supply or maybe with the original conditions, everything works ok, but the original RC value is already a bit too low compared with what is recommended in the 8085 documentation.

    I'm no expert into these designs, but in my opinion maybe the open-collector last inverter with its own pull-up makes not a lot of sense. This should be in some way isolated from the CPU-Board reset circuit but with the current design, any board that wants to be able to reset the system, will put a resistor in parallel to the reset RC network, hence making the rise-up time shorter and shorter.

    I'm glad you find useful the data I'm able to slowly extract from the Alphatronic system. To be honest, if the computer worked properly day one, I would have tested some CP/M programs on it and it will be now sitting there, probably I wouldn't have learn anything from it. :)

    Ja, prima overCLK - das Endergebnis liefert nun ein sicherstes

    RESET-SIGNAL nach dem POWER ON von dem externem PSU.

    Was ist noch an welche Probleme zu lösen sind?

    Danke helwie44 †.

    Nächster Schritt wird der Speicher sein. Ich will alle die Tantal-Kondensatoren wechseln.

    Damit muss ich zuerst identifizieren, welche Kapazitäten und Spannungen die ursprünglichen haben.

    Vielleicht brauche ich da Hilfe. Besonders mit dem Kondensator, der verbrannt wurde. ;)

    Ja, das sieht doch ähnlich aus. :)

    Ich glaube, dass ich das Problem mit dem Reset bei der Einschaltung gelöst habe!

    Zuerst habe ich das Schaltung des Resets nochmal analysiert.

    Da kann man sehen, wie die Reset-Zeit mit einem RC-Glied kontrolliert wird. Je grösser das Produkt RC bekommt, desto länger ist die Reset-Zeit. Auf dieser Fall ist die Zeitkonstante 47K . 100 nF = 4.7 ms

    Aber wenn man die Tastatur-Kontroller-karte einsteckt, dann ist das Schaltung des Resets anders:

    Mit der roten Farbe habe ich ein neuen Widerstand (2K2 + 56R) markiert, der parallel schaltet wird. Das bedeutet, dass die RC-Glied anders ist, und die Zeitkonstante viel niedriger bekommt (circa 215 uS).

    Deshalb sieht es aus, dass die Reset-Zeit unter diesen Bedingungen zu kurz sein könnte.

    Mit dem Oszilloscop habe ich geprüft, dass die Reset-Zeit ganz anders ist.

    Mit der Tastatur-Karte (+5V Signal im gelb, Reset-In im blau)

    Ohne die Tastatur-Karte:

    Da kann man sehen, wie das Reset-In-Signal langsamer einsteigt!

    Endlich habe ich die Reset-Kondensator mit einem 10uF Kondensator gewechselt, um das Reset-Signal zu verlängern.

    Es hat prima funktioniert! Jetzt bekomme ich ein richtiges Reset bei der Einschaltung. :prost:

    Ich vermute, dass vielleicht es richtig mit dem ursprünglichen Netzteil funktioniern würde, weil die "Ramp-up" des 5V signal anders sein könnte. Je langsamer die 5V kommt, desto länger wird das Reset-Signal sein.

    Hier auch die Verbindung des Pins B14 (Reset-In) in der Tastatur-Kontroller-Karte.

    Da kann man sehen, wie ein Signal von der Tastatur mit B14 verbinden ist. Es gibt zwei verschiedene Inverter dadurch. IC4 ist ein 74LS05 (Inverter mit Open-Collector-Ausgang) und IC5 ist ein 74LS14 (Schmitt-Trigger Inverter). Es gibt auch inzwischen einen Widerstand (56 Ohm) und einen anderen Widerstand, der als Pull-up funktioniert (2200 Ohm).

    So funktioniert es, wenn man die Reset-Taste drückt. Ein Reset-Signal kommt in RESET-IN der CPU (B14). Die 8085 aktiviert RESET-OUT, dass dem Reset-Pin (4) der 8278 reicht (durch B15).

    An der Anschaltung sollte es mehr or weniger dasselbe sein. Ich vermute, dass vielleicht das Reset-Signal in dieser Situation nicht genug dauert. Vielleicht kann ich morgen einige Testen machen.

    Three are two reset signals on the bus, B14 and B15. One of them should be coming from the 8085, as it had a dedicated reset line ti initialize peripherals. The other one I don't know, if it does not initializes the CPU I simply don't know what's its purpose.

    I've just tried to follow the tracks on the CPU board:

    B14 is bound to the 8085 pin 36 (RESET IN) through what it seems to be a 60R resistor and following the recommended circuit for 8085 reset. Therefore this is the reset input to the main processor.

    B15 is bound to the 8085 pin 3 (RESET OUT) through a SN74LS04 hex inverter (pins 8 and 9). So, this is an output reset feature.

    Maybe this reset out is bound to the proper pins in video and keyboard cards. Anyway, I think that the problem is that the CPU doesn't reset properly for whatever reason.

    Track study follows:

    CPU Board (Pins B14 and B15):

    Keyboard Board (Pin B15). B15 goes through two inversions in a 74LS14 and then into the /RESET pin of the 8278 Keyboard controller. Looks reasonable, doesn't it? :)

    You're welcome. This is in fact an interesting discussion.

    At the end, custom chipsets were there to save costs and power consumption. We can either emulate the bare 74LS logic or the custom chipsets with CPLD/FPGA solutions. Do I like it? Well, it's a solution. What I don't like is hearing that this is the real thing, like I have heard lots of times. It's just emulation at a different layer, is'nt it? ;)

    I have one of my Spectrum ZX running on a Nebula replacement and it's somehow a satisfactory approach. It would be better to have the real thing, but… from an user perspective you cannot tell the difference unless we are talking about some artifacts of the original device. But for 99,9% of the requirements, it is OK.

    And at the end, at least in my case, I do this just for fun. And trying to implement a system or part of it on CPLD/FPGA logic can also account for fun. And it forces us to understand all the low level details of the target system.

    What I'm not for is a methacrylate box emulating everything on a chip, with HDMI output and not even the original I/O ports. But of course I understand they also have their addepts, and I'm not against it. But I think the original spirit is somehow lost. :)

    Anyway, let's see what the future brings. But what today is stock material, maybe it's not anymore in some years.

    Interesting thoughts.

    I guess the situation will become more or less the same for other computer systems. It's even worse for those that are not easy to find, or used not the most common hardware solutions.

    The problem is that as time goes by, replacements will be more and more difficult to find. Nowadays it's easy to find for instance, any DIP packaged 74LS chip, or the most common processors/controllers of the 80's. But I fear that it will become more and more difficult in the future.

    So maybe in some years, we will have to rely to emulation (software or CPLD/FPGA) to keep the computer running. I consider that emulating by hardware a whole system like the Alphatronic P2, specially with the documentation currently available, is a huge task, but maybe the future only option. There are, of course, lots of possibilities:

    - Keep the main chips (controllers, , emulate the additional logic with CPLDs) and provide replacements based on CPLD + main chips for the different cards

    - Just emulate the whole system on a single chip (FPGA), but providing connectors for the representative parts (floppy, composite video,...) or even provide a backplane replacement enabling old working cards to be connected (disabling emulation for those parts).

    Regarding the case, I suppose that nowadays plastic injection molding is the only technique providing a decent result. I made 3D printed replacements for some computers (half a case for an Atari ST somebody cut away), or cases for different peripherals,.. but of course it's not the best solution (it's a home printer anyway, maybe the professional ones provide better results). Plastic injection seems to be also very expensive unless you have a good amount of requests. The Alphatronic P2 has additionally a huge case. :)

    But at least for me the question is, at what extent a computer is still the same computer if we replace its components. :)

    I'm OK with changing the power supply, or replacing a floppy drive with a more practical emulated solution(flashfloppy, Hxc). But replacing the brain of the computer with something emulated… that is another story. Of course if there is no other option, I would be ok with a new brain as far as I could keep the case and the keyboard as it is. I would also replace the CRT with a LCD solution, keeping the same case.

    For me, the retro computing is a lot about the feeling. I don't feel the same touching my very first Amstrad CPC6128, or typing on my Northstar Advantage (the first one I used at school) than on some software-emulator. It's about the noise they make when you turn them on, the feeling of the keys, the ritual of inserting a disk in the drive, typing a command, and hear the disk spin and the head moving (even how the CRT smells when it gets warm),... Feelings that bring me back to that age. Yes, sorry, I'm getting old. :)

    But of course, nothing lasts forever (and neither do we). And being able to keep the original ROM contents and emulate all the peripherals would be enough to at least keep some distant echo of how the thing looked like and worked. Let's say we will have a photo of the real thing, but not the real thing.

    Just my two cents. ;)

    Three are two reset signals on the bus, B14 and B15. One of them should be coming from the 8085, as it had a dedicated reset line ti initialize peripherals. The other one I don't know, if it does not initializes the CPU I simply don't know what's its purpose.

    Thanks, I will check. That means that probably the CPU is not properly initialized on power up, and having the keyboard card in or not makes a difference!

    About capacitors exploding. Are you using the original PSU, right? I realized that every time we turn any of the P2 we have we do it with a regulator.

    No, that one passed away a while ago. It seems to be shortcut because it blows the main fuse immediately, even without no other thing connected to the backplane. :bekehr:

    I'm using a PC ATX power supply. I don't know what are the specs of the original power supply but I guess the capacitor shortcut brought a lot of current on the 12V backplane track destroying it. That is why I initially thought that the 12V power supply rail was dead. I was surprised to find out that with a new power supply I was still missing the 12V voltage. I finally found that the tiny track between two of the backplane slots joining the 12V pins was gone for good. This is why I'm wondering if maybe the short circuit current of a PC power supply is way too much for the old and tiny tracks of the backplane.

    The capacitor actually catched fire and I had to blow to extinguish it before it reached the video board (it got a bit black on one corner). :abrauch:

    Komische Linien auf dem P2 Display

    Weil offenbar vom POWER ON kein richtiges RESET-SIGNAL auf den BUS kommt, sind in den Video-Chip-Registern (memory-maped) undefinierte (Zufall) Werte. So wird das Bild auf dem Display wie „komische Linien“ angezeigt.

    Erst mit der Reset- Taste von der Tastatur wird der CRT-Chip richtig initialisiert.

    Ja, ganz einverstanden. Dass muss der Grund sein. Was jetzt zur Frage steht, warum es eigentlich passiert:

    Ich verstehe, dass der Reset-Kondensator an der Anschaltung das CPU-Reset-Signal generiert. Das ist offensichtlich genug um die CPU-Karte richtig zu initialisieren, am mindestens wenn keine Tastatur-Kontroller-karte hineingesteckt ist.

    Konnte es sein, dass wenn die andere Karte auch hineingesteckt sind, ändert sich das Reset-Signal, und reicht es nicht, die CPU-Karte zu initialisieren? Wie sind theoretisch die andere Karte initialisiert? Nützten sie dasselbe Reset-Signal oder kommt etwas anderes aus die CPU-Karte?

    Evtl. habe ich einige Unterlagen von dem DS2069 Sichtgerät ( ähnlich dem KISS und den TA P2 Systemen) für ein Tastatur-Controller. Dort sollte die „Reset-Schaltung“ als Hintergrundinformationen zu finden sein.

    Ja, dass könnte vielleicht hilfreich sein!

    Ich bin gleich vom Geschäft gekommen, und habe ich den 74LS85 Ersatz installiert.

    Es freut mich sehr zu sagen, dass die Tastatur-Karte wieder im Betrieb ist. Nach Hard-Reset habe ich das Pfeifen gehört und den MOS Meldugen gekommen und die Tastatur funktioniert richtig!!

    So, den ersten Schritt haben wir gut geschafft! :)

    Ich brauche noch die RESET-Taste drücken, um der Rechner richtig zu starten, anderenfalls bekomme ich nur komische Linien im Bildschirm, als ob er nicht richtig synchronizieren könnte.

    Ich muss jetzt um den Speicherkarten kümmern, neue Kondensatoren zu kaufen und mal sehen …

    Es war aber aufregend, der Rechner wieder starten zu sehen. Vielen Dank für die Hilfe und Unterstützung.

    Ich habe auch getestet: Mein Rechner zeigt bei entfernter Tastatur-Karte nach der MOS Meldung ebenfalls kontinuierlich ".2" an. Das ist also die MOS Fehlermeldung für "Tastatur-Karte fehlt". Insofern ist Dein Rechner sonst offensichtlich in Ordnung, Du brauchst also zumindest keine Fehler auf dem CPU Board suchen. Es muss tatsächlich ein Problem auf der Tastatur-Karte sein. Sobald dieses behoben ist, sollte die MOS Startmeldung und Eingabebereitschaft für MOS Befehle korrekt ablaufen.

    Wenn ich die Tastatur-Karte einstecke und das Kabel zur Tastatur nicht anschließe, dann kommt bei mir einfach nur die MOS Bootmeldung. Weder "garbage on screen" noch laufende ".2".

    Hallo gpospi. Vielen Dank für den Test. :)

    Ich glaube, dass der Grund einen "2" zu bekommen ist eigentlich was im Daten-Bus gibt, wenn das CPU die I/O Operation läuft. Wenn das Tastatur-Karte zur Verfügung steht, dann wird die Informationen im Addressen-Bus dekodiert um der Tastatur-Kontroller zu aktivieren. Dann bekommt man die Tastatur-Kontroller FIFO Informationen im Daten-Bus (gedrückte Taste). Anderenfalls Daten-Bus wird irgendwas halten, was wahrscheinlich auf Daten-Bus Standardeinstellung angeht.

    Es ist doch interessant zu wissen, dass du kein "garbage on screen" bekommst, wenn die Tastatur nicht eingesteckt ist. Das ist hier anders.

    Hallo helwie44 †. Meine Antworten:

    Sind die jetzt +5v, +12V und die -12V im System-BUS stabil über einige Testzeiten?


    aa) Mit POWER ON startet doch das MOS mit den richtgen Meldungen ( richtger Speicher - Ende?

    Dann loop eine Zeile mit dem MOS-PROMT also den . (Punkt) und ohne was zu machen, wird immer ein ZEICHEN "2" angezeigt - ist doch richtig?

    Ich muss die Reset-Taste drücken, anderenfalls bekomme ich kein Bild. Nachdem ich die Reset-Taste gedrückt habe, dann bekomme ich die Meldungen und Zeile mit dem Punkt und "2", wie du es beschreibt hast.

    bb) Mit HARDRESET KEY wird die CPU gestartet?

    Ja, genau. Das ist nicht nötig, wenn die Tastatur-Karte nicht eingesteckt ist.

    cc) WICHTIG!! Ist es per Hand eine Taste einzugeben, also dazwischen dem laufenden Ausgaben der "2" z.B. "D" isplay oder "F" ill oder beliebige andere TASTEN möglich?

    Nein. Egal was man auf der Tastatur druckt, nur Punkte und "2" symbol.

    TT. Wie ist das Ergebnis - wenn alle Karten eingesteckt sind (auch KEYBOARD Card) aber nur das FLACHBAND-Kabel abgezogen wäre? Klar dann könnte kein KEY RESET möglich sein. Aber endet der loop mit den "2" damit. ??

    Dann bekomme ich nur Müll im Bildschirm.

    Ich glaube, dass ich ein Fehler im Tastatur-Kontroller gefunden habe: Mit dem Oszilloscop habe ich gesehen, dass der /CS pin im Tastatur-Kontroller (8278) wird nie aktiviert. Dass kann nicht sein, als damit kann das CPU überhaupt nicht richtig Informationen aus der Tastatur-Kontroller lesen oder schreiben.

    Ich habe untersucht, wie das Signal /CS generiert wird. Es gibt dafür verschiedene Bausteine benutzt (74LS155, zwei 74LS14 und ein Komparator 74LS85). Aber endlich habe ich gefunden, dass der 74LS85 (IC8) schuldig sein könnte, weil es immer ein Null ergebnis gibt, wenn er die Signale der Addresse-Bus A3, A4, A5, A6 mit 0, 5, 0, 0 vergleicht. Dass kann nicht sein, weil die Signale der Addresse-Bus sich ändern.

    Deshalb habe ich der 74LS85 gezogen und einen Sockel im Platz verlötet.

    Jetzt muss ich einen Ersatz kaufen. Morgen frage ich mal in einem Geschäft, dass nicht zu fern von hier liegt. Wenn dort kann ich der nicht finden, dann muss ich ein bisschen warten. :(

    Später antworte ich gerne eure Frage. Danke für alle die Unterstützung. :)

    My 48K RAM card also had 2 defective capacitors (luckily without "explosions"), but I removed them and now it works. I am confident that your's will also still work. Good luck with the next attempts!

    I'm back on the road. :)

    Finally the power supply was not the problem. I prepared a new one today, connected everything and was astonished to find that there was still no 12V on the backplane. :fp:

    Checked the power supply alone and I got the 12V (what is going on?). Finally the problem was that the backplane 12V track between slots 3 and 4 was not able to handle the amount of current during the capacitor issue and got burnt and destroyed.

    I restored the track with a cable. All tensions available!! ::solder::

    The computer is able again to reset and delight me with an endless screen of "2". :hüpf:

    Lessons learned:

    - A PC power supply with 12V 10A is able to easily destroy the delicate backplane 12V tracks on a short circuit scenario.

    - Could it be a good idea to dry test dodgy cards by providing just the voltages to see if something is really wrong? I mean, just connect the voltages out of the backplane.

    Key Statusport wird gepollt.
    Im MOS werden bei der Tastenverarbeitung nicht über Interrupts abgewickelt! Das Tastenport (Statusport) wird im MOS gepollt. Vom Layout evtl. anderer CPU Cards wäre es möglich ( z.B. 8259 IR-chip später?) IRQ abarbeiten.

    Danke helwie44 †! Denn vermute ich, dass es vielleicht ein Problem mit der Portdecodierung ist. Nachdem ich ein anderes Netzteil bekomme, will ich diese Möglichkeiten untersuchen.

    Just for comparison I am attaching the "backside" picture of my CPU board. Maybe the keyboard is (or should be) being polled by the CPU, hence IRQs would probably not be needed. I think this was a common approach in such old computers, but probably helwie44 † can check/confirm for the P2.

    With the EPROM size I agree, I just couldn't read the type name in your picture. In total it must be 6K, but of course 4K+2K is also possible ;)

    Actually this is the backside picture of the second CPU card (lower picture in my previous post), which is working. The upper CPU card shown in my previous post (with the "missing" solder jumpers) is not working at all, even if I replace CPU and ROMs with the working ones from the other card.

    Thanks for that. It's basically the same layout regarding IR0-IR7. It seems a topic to research. :)

    Some minutes ago I tried to plug in the 48K RAM card, just to see if it made any difference on the reset message and one of its tantalum capacitors exploded and got fire. I switched everything down and put the fire out as soon as possible and removed the card. I'm sure I tested those capacitors for shortcuts some weeks ago but still, I suppose these old tantalum capacitors are like dormant bombs. :(

    I was just wondering why should I need to try this card now, but actually I will eventually try to plug it in to see if it worked, so, this was something it couldn't be avoided, I'm afraid. :(

    Computer went dead again. It seems that the 12V line of the power supply is broken and let's hope that is the only damage. That was enough for today friends.

    And looking into this photo of one of your CPU cards, it seems that IR0-IR7 can be controlled by solder jumpers, but none of them is set... even more confusing. :)

    But maybe this is the same idea in my card, but on the solder side, because there is a vertical track going to nowhere that maybe it plays the same role. But I don't understand how come the keyboard board routes the IRQ to IR0 and then the CPU doesn't have this pin routed. Maybe it's not even needed...

    Regarding the capacitor for the reset circuit, you can find it by looking for one attached on the positive pin to the CPU pin 36 and the negative pin to ground.

    Now I am completely confused with the CPU card picture. Both of my CPU cards actually have 3 EPROMs, but yours shows only 2 and the space for the third socket is empty. Maybe this explains the ".2", i.e. computer complains that only EPROM 0 and 1 are found and 2 is missing? I might check with my CPU card if I find some time...

    Probably a matter of different revisions (mine is a CAAA06 and one of yours seems to be a CAAA02) and probably using different EPROM capacities? Mine has a AM2716 (2Kbytes) and a HN462532 (4Kbytes).

    I got the connector via Ebay, sold by "compon07" (seem to be sold out at the moment). But there are other sellers on Ebay with similar pricing, e.g. chipmarktgmbh (…ldet-HARTING/223531714357).

    Vielen Dank! :)

    Now, this is really confusing… :)

    I've tried to follow the backplane IR0 connection into the CPU board, to find just what I'm showing in the included photo.

    On the components side there's nothing coming out of IR0-IR7, in the tracks side, as you can see, IR0-IR7 have all a short track coming down and left but… it seems there is no connection to anything. is this expected or do I miss something in my CPU board? Could you check how are yours? Or aren't IR0-IR7 routed to the CPU board at all? Doesn't make sense to me, since IR0 is where the keyboard controller IRQ is mapped out, so...

    Actually the connector was 3,5 EUR plus 3,5 EUR shipping.

    Maybe I should also replace the reset capacitor, I am not sure if the "manual reset" is fully equivalent.
    Can you post a picture of the CPU board showing which capacitor you actually replaced (and maybe also the capacity that you are using)? I have two CPU boards (the working one and the broken one), but they have quite different layout.

    That is a good price. Do you mind sharing the buyer contact (in case it's allowed here)? :)

    Regarding the reset capacitor, it's the one near the CPU top side (green tantalum capacitor marked as ",1 35V". It is a 100nF capacitor but reading the specs of the Intel 8085 it seemed to me a bit too low and tried with a 1uF electrolytic one (as seen in the aforementioned 8085 manual) to see if it made any difference in my first tests.

    What I don't know if it would work with the original one (actually the measurement I get from it is near its nominal value).

    Well, I've made some new observations:

    - The demuxers in the keyboard board seems to generate signals consistently.

    - The i8278 is generating also good looking scan values for the demuxers.

    - When a key is pressed on the keyboard, i8278 RL is going active as expected. The IRQ line of the 8278 goes high, but it never went low again. I understand it means nobody is reading the FIFO (the CPU should do it I guess).

    In the keyboard controller board pin 23 of the i8278 is connected to an input of a 74LS04 hex inverter, and the inverted output goes to pin IR0 of the backplane. I've checked than whenever a key is pressed this backplane signal goes low (negative logic) to never return high again.

    It seems to me that the request from the keyboard is reaching the backplane, but nobody is taking care of reading the keyboard (or maybe the keyboard board is just malfunctioning, but I don't think so). Now I need to understand how the interrupt logic works, and how the IR0-IR7 signals in the backplane are mapped to the CPU, and what to check on the CPU side. I've seen no INTR/INTA activity on key presses, but I'm not sure if IR0 should be routed here somehow.

    Do you know how IR0-IR7 are related to the 8085? I think the problem could be there.

    Hallo helwie44 †. Vielen Dank für die Informationen und Ideen.

    Ich glaube auch, dass es ein Problem mit der Tastatur-Kontroller-Karte gibt, oder vielleicht einige der Bausteine in der Tastatur-Board (aber auf diesem Fall sollte ich einen akustischen Piepton bekommen, oder?)

    Heute möchte ich noch probieren, ob die Signale auf diese Bausteine normal aussehen. Ich habe auch im eBay einen Ersatz für die Tastatur Kontroller (Intel 8278) gefunden. Ich habe es sofort gekauft und es war schon geschickt. Mal sehen wie es gelingt. :)

    I paid 7 Euro for the Harting connector including shipping, a fair price in my opinion ;)

    BTW, I noticed another interesting fact: You write that your P2 runs a proper reset cycle (and shows the MOS screen and the .2 messages) when the keyboard card is removed. My machine (with German ROMs) is different, it requires a manual reset via the reset button. Without manual reset the screen remains black and the computer doesn't start at all, hence I can't confirm if the polling of the missing keyboard card produces any output on the start screen (as written in helwie44 † 's manual).

    Well, 7€ is not cheap for a connector, but even reasonable. I have seen quite more expensive. ;)

    Regarding the reset, I can confirm that: my machine resets on startup when no keyboard card is plugged in. I have to say that I replaced the reset capacitor in the CPU card. The original one (a tantalum one) was giving a very low capacity and probably leading to a very short reset pulse. But maybe there is another reason…

    For my second project (building a P2 into a PC case due to missing original case), I just ordered the original internal PSU connector. It is called "Harting 09041326921" or "DIN 41612" (32 Pin, 6A, MALE). Then I just soldered the necessary lines from the PC PSU to this connector. This allows me to connect the PC PSU directly to the backplane, exactly as the original PSU cards were connected.

    Regarding the ".2": I am not sure that I understood your approach correctly. If you get the ".2" also with removed keyboard interface card, the problem obviously is not in the keyboard interface card.

    When I have my keyboard interface card in the computer without connecting the keyboard, I get no garbage on the screen but the computer simply doesn't reset (i.e. no output at all).

    Something seems strange with the memory in your machine. If you would insert a 48K card, it should write "FFEF". With a 16K card the correct output is "40EF" (not "40FF").

    Yes, I found somewhere those connector, but at least where I found them they costed an arm and a leg. :)

    My intention was to replace the backplane connector (actually any 5.08 mm pitch connector will do, but the ones I bought are a bit too wide), but it seems it's not easy to remove them. I just feared I could damage the backplane so I opted to solder on the backside.

    I don't see it that clear. The thing is that after reading the documentation on troubleshooting from helwie44 †, I understood that on no keyboard card present, you get something like a wrong keyboard input. Since I'm getting the same result no matter the keyboard card is connected or not, I understand there is something wrong with it. Doesn't it make sense?

    Regarding memory, I'm testing with only three cards in: CPU, Keyboard and Video. I just prefer to go step by step. :)

    Congrats! Those are great news! Shame I ran out of cider yesterday…

    Thanks a lot. It was really unexpected to see some life after pressing the reset key. :applaus:

    Is normal for it not resetting on startup without the 12V card, so it shouldn't be an issue. However, not having the beep is not good...

    But it does it when the keyboard card is not present. Is that also normal? Actually it seems that the keyboard card is just preventing the normal reset, and after that it works the same whether the card is present or not. Just an endless loop of ".2" lines.

    What is the root reason for the computer not properly resetting on absence of the 12V card? Do you know it?

    Yes, regarding the initial beep, I've never heard it from this computer yet. :(

    I will try to do some research on the keyboard card operation.

    Well, after all this time, I finally received the connectors I wanted to use to bind a PC power supply to the backplane.

    I prepared a PC power supply by removing all the unneeded cables and then I tried to desolder the backplane connector where the +12/-12 original power supply card is connected. Unfortunately it is not that easy and I decided not to do it (after removing all the solder, it didn't came out, probably because of the sort of rivets on both sides of the connector). Instead I soldered the new connector in the back side on top of the proper pin ends (not a very nice solution, but now I have steady +5,+12,-12 supply through the whole backplane and also on the drive connectors).

    Once I checked the voltages I connected the CPU, keyboard and video cards. Switched on and... nothing. The scope detected consistent activity in the 8085 (CLK out was there, ALE was changing all the time). I pressed the reset button on the keyboard and suddenly, the reset message appeared and was fastly scrolled due to incoming lines with only ".2" in. So, the screen was something like:

    $1976 4010 40FF

    Great! At least is seems that the CPU card is working, the video card is working, and the keyboard seems to be the issue. I made the following tests:

    - With the Keyboard card in, the computer doesn't reset on startup. Only by pressing the RESET keyboard key you get the reset sequence. There is also no beep on startup.

    - With the keyboard card out, the computer resets, and you get the same result as when the RESET keyboard is pressed: An infinite loop of ".2" lines.

    - With the keyboard card in but the keyboard disconnected, I just get garbage on the screen.

    So, it seems that something is wrong with the keyboard card. Any idea of how to troubleshoot it?

    Anyway, I was really happy and excited to see some activity on the screen. Still a long way to have it completely working but we are on the way. :)