Geschichte eines Alphatronic P2, der eine Reparatur (oder mehr) versucht.

    Vor einigen Wochen habe ich einen Alphatronic P2 gekauft. Der Verkaufer sachte, dass der Komputer im Betrieb war. Leider bedeutet es nur, dass der Lüfter läuft beim Einschalten (er hat sogar kein Videokabel). Un das war alles...:nixwiss:


    Erster Versuch.

    Als ich mit dem Computer nach Hause gekommen bin, habe ich ihn geoffnet, um der Zustand auszuwerten.

    Als alles gut genug aussah, habe ich den Computer anschalten. Die LED der Tastatur leuchtete, der Lüfter läufte, aber es gab weder kein Videosignal noch Ton zu sehen oder zu hören.

    Nach einige Sekunden ist etwas gebrannt. Rauch kommt von der Nähe des Netzteils und auch ein schreckliches Gestank. Der Kondensator des Funk-Entstörfilter hat sich umgebracht.


    Noch mal.

    Nachdem ich einen Ersatz bekommen habe und beide RAM Karten herausgezogen, habe ich ihn wieder anschalten:

    - Kein Videosignal, kein Ton.

    - Ich habe +5V, +12V, +12V Spannungen in die Backplane gemessen.

    - Das Oszilloskop zeichnet keine Bewegung aus Pin ALE der 8085 Hauptprozessor. Meine Vermutungen:


    -Der CPU ist irgendwie kaputt. Es konnte sein, aber gleich an der Anschaltung kann mann trötzen Aktivität auf ALE sehen.


    -Das Reset funktioniert nicht gut. Normalerweise braucht eine CPU etwas Zeit im Reset zu stehen, um richtig zu starten. Zeit des Resets wird bei einem Kondensator kontrolliert. Ich habe der Kondensator des Resets herausgezogen um es zu messen. Un ja, der Messegerät gibt nur 89nF statt 1uF! Vielleicht der Tantal-Kondensator ist kaputt gegangen... Ich habe ihn mit einem 1uF Electrolyt-Kondensator ausgetauscht aber das selbe Ergebnis bekommen.


    -Vielleicht kommt die CPU im Status HALT. Ich eigentlich weiß nicht, ob es Aktivität auf ALE während HALT gibt. :?:Deshalb wollte ich mit dem logischen Analysator die Startreihenfolge untersuchen.


    Als Hilfe habe ich auch einen Plan der Verbindungen gezeichnet. Es steht hier zur Verfügung: https://www.dropbox.com/s/mdp0g039oj13erf/backplane.png?dl=0


    Es wird noch schlimmer.

    Dieses mal hat plötzlich der Lüfter beim Test gestoppt. Ich habe gefunden, dass die Hauptsicherung gebrannt ist. Dann habe ich drei Ersätze gekauft aber leider kein Glück. Die neue Sicherungen haben sich sofort beim Einschalten ums Leben gebracht. Der letzte Versuch habe ich mit alle die Karte raus (nur die +5V Netzteil war drin) gemacht. ::cry::


    Es sieht aus, dass der Netzteil kaputt geworden ist. Keine Spur aus visuelle Beobachtung. Der nächste Schritt würde, ein PC Netzteil als Ersatz zu benutzen, um die Teste wieder zu machen. Ich will auch das Problem des Netzteils untersuchen.


    Es wird weitergehen. :)

    Ich würde jedenfalls auch mit einem PC Netzteil testen. Und nach dem Einschalten sollte links an der Tastatur eine LED an der Reset-Taste (c) leuchten (im Bild mit dem roten Kreis markiert). Diese Taste kurz drücken, danach müsste der Computer piepsen und den MOS-Startbildschirm anzeigen.

    Bitte systematisch prüfen..


    A) Steckkarten alle raus!

    Um eine optimale Reihenfolge bei Startproblemen einer alphaTronic P2 zu prüfen, habe ich hier eine MEMO-PDF (english) aus 2016 erstellt. Wenn hier sofort die Sicherungen fliegen, müssen im ausgezogenen Zustand die Steckkarten (KBD, RAMs, CRT, FLOPPY, CPU - Karten) auf Kurzschlüsse ( meist Kondensatoren- Probleme) geprüft werden. Meist reicht dafür ein Ohmmeter.


    B) NETZ-Module für +5V, +12V, -12V prüfen!

    Das wäre eine gute Idee.

    Quote from overCLK

    Ich will auch das Problem des Netzteils untersuchen.

    Klar im Leerlauf ( alle Karten und Floppylaufwerke raus) sollten zunächst die Netzmodule genauer zu untersuchen und wenn möglich defekte Teile auszutauschen. Wenn da nichts zu machen wäre - ist eine ( jlopez , gpospi ) ,externe Gleichspannungversorgung moglich.


    Ich denke, wenn nach A) und B) alles ok wäre und immer noch kein MOS-START auf dem Display zu sehen wäre - könnte man mit einen Logic-Analyser oder Scope einsetzen.


    Hinweis - kein Thema da zu finden.

    (Der DROPBOX -LINK von overCLK ist hier eine WEB-Firma und nicht auf ..Plan der Verbindungen ???)


    Viel Erfolg

    Helwie44

    Quote from gpospi

    Ich würde jedenfalls auch mit einem PC Netzteil testen. Und nach dem Einschalten sollte links an der Tastatur eine LED an der Reset-Taste (c) leuchten (im Bild mit dem roten Kreis markiert). Diese Taste kurz drücken, danach müsste der Computer piepsen und den MOS-Startbildschirm anzeigen.

    Das ist ja eine gute Idee, und auch was ich anschließend machen will. Wie hast Du eigentlich das PC Netzteil verbunden? Meine Idee wäre, es direkt auf der Rückwandplatine zu verbinden. Ich weiß aber nicht, was für Konnektoren könnte ich benützen.

    Ja genau, ich habe das PC Netzteil direkt mit der Backplane verbunden. Dazu habe ich ganz rechts den leeren Anschlussplatz verwendet. Ich habe einfach Drähte in die entsprechenden Anschlussöffnungen gesteckt und mit dem PC Netzteil verbunden (also Anschluss 1a/1b mit +5V, 2a/2b mit GND, 3a/3b mit +12V, 5a/5b mit -12V). Die Alphatronic Floppy Laufwerke bekommen so keine geeignete Stromversorgung, daher habe ich hier direkt die 4-poligen Floppy/Harddisk-Stromkabel des PC Netzteils angesteckt.

    Quote from gpospi

    Ja genau, ich habe das PC Netzteil direkt mit der Backplane verbunden. Dazu habe ich ganz rechts den leeren Anschlussplatz verwendet. Ich habe einfach Drähte in die entsprechenden Anschlussöffnungen gesteckt und mit dem PC Netzteil verbunden (also Anschluss 1a/1b mit +5V, 2a/2b mit GND, 3a/3b mit +12V, 5a/5b mit -12V). Die Alphatronic Floppy Laufwerke bekommen so keine geeignete Stromversorgung, daher habe ich hier direkt die 4-poligen Floppy/Harddisk-Stromkabel des PC Netzteils angesteckt.

    Sorry for my English here.


    This solution sounds nice. Cleaner than the one published by me. If a 555 circuit is placed, reset pulse could be easily generated, so no more "manual reset" anymore. :S

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Das ist eigentlich was ich getan habe. Das Problem ist, dass noch mit alle Karten und Floppylaufwerke raus wird die Hauptsicherung sofort durchgebrannt.

    Ich glaube, dass am besten sollte ich mit einem PC Netzteil versuchen. An mindestens weiß ich damit, dass die Spannungsversorgungen richtig sind.


    Danke nochmal für deine Unterstützung und Ideen.



    Quote from helwie44

    Hinweis - kein Thema da zu finden.

    (Der DROPBOX -LINK von overCLK ist hier eine WEB-Firma und nicht auf ..Plan der Verbindungen ???)

    Ich habe leider der Link nicht richtig stellen. Und jetzt ist es nicht länger möglich, er zu bearbeiten. Es funktioniert, wenn man den Text der Link kopiert. Da stelle ich noch mal der Link.


    https://www.dropbox.com/s/mdp0g039oj13erf/backplane.png?dl=0

    Quote from gpospi

    Ja genau, ich habe das PC Netzteil direkt mit der Backplane verbunden. Dazu habe ich ganz rechts den leeren Anschlussplatz verwendet. Ich habe einfach Drähte in die entsprechenden Anschlussöffnungen gesteckt und mit dem PC Netzteil verbunden (also Anschluss 1a/1b mit +5V, 2a/2b mit GND, 3a/3b mit +12V, 5a/5b mit -12V). Die Alphatronic Floppy Laufwerke bekommen so keine geeignete Stromversorgung, daher habe ich hier direkt die 4-poligen Floppy/Harddisk-Stromkabel des PC Netzteils angesteckt.

    Danke dir! Meine Idee wäre mehr oder weniger dieselbe. Aber ich würde lieber die beide linke Anschlussplätze benützen. Da kann man auch +12, -12 und +5V Anschlussstelle finden (auch für die Diskettenlaufwerke).

    Quote from jlopez

    Sorry for my English here.


    This solution sounds nice. Cleaner than the one published by me. If a 555 circuit is placed, reset pulse could be easily generated, so no more "manual reset" anymore. :S

    Hmm, and why is that needed? Shouldn't we get a pulse in the 8085 reset pin just by means of the reset capacitor in the CPU card? I mean, what changes because of the PC power supply?


    Cheers

    Edited once, last by overCLK ().

    Quote from overCLK
    Quote from gpospi

    Ja genau, ich habe das PC Netzteil direkt mit der Backplane verbunden. Dazu habe ich ganz rechts den leeren Anschlussplatz verwendet. Ich habe einfach Drähte in die entsprechenden Anschlussöffnungen gesteckt und mit dem PC Netzteil verbunden (also Anschluss 1a/1b mit +5V, 2a/2b mit GND, 3a/3b mit +12V, 5a/5b mit -12V). Die Alphatronic Floppy Laufwerke bekommen so keine geeignete Stromversorgung, daher habe ich hier direkt die 4-poligen Floppy/Harddisk-Stromkabel des PC Netzteils angesteckt.

    Danke dir! Meine Idee wäre mehr oder weniger dieselbe. Aber ich würde lieber die beide linke Anschlussplätze benützen. Da kann man auch +12, -12 und +5V Anschlussstelle finden (auch für die Diskettenlaufwerke).

    If you had scrapped a PC you could solder its PSU connector with a few wires on the back of the backplane so you wouldn't have to cut its connector or have unstable wires.

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Like 1
    Quote from jlopez

    If you had scrapped a PC you could solder its PSU connector with a few wires on the back of the backplane so you wouldn't have to cut its connector or have unstable wires.

    Yes, sure. Anyway I would like to see if there is an option to connect them on the front side. At the end I will probably have to build some replacement to be located where the original power supplies are. I will take a look to my stock to see if something could fit. Otherwise I will go for the back soldering solution.


    Thanks a lot!

    Quote from overCLK
    Quote from jlopez

    If you had scrapped a PC you could solder its PSU connector with a few wires on the back of the backplane so you wouldn't have to cut its connector or have unstable wires.

    Yes, sure. Anyway I would like to see if there is an option to connect them on the front side. At the end I will probably have to build some replacement to be located where the original power supplies are. I will take a look to my stock to see if something could fit. Otherwise I will go for the back soldering solution.


    Thanks a lot!

    The original connector you are seeking is a Harting, 32 pins arranged in 16 x 2, if I recall correctly.

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Like 1

    Yes finally I would also consider using a 16x2 connector or a proper 32x3 connector. I just started to build my replacement power supply connection as quickly as possible, without waiting for parts to be delivered. In addition I have a "space problem" at the left side of the chassis (where the original power supply and the 16x2 connector are located), as I mounted my ATX power supply exactly at this location. Therefore it is more convenient for me to have all connector pins at other locations of the backplane (giving me access any time without removing the power supply). The PC power supply is just small enough to fit into the Alphatronic case without any further modifications ;-).

    Quote from gpospi

    Yes finally I would also consider using a 16x2 connector or a proper 32x3 connector. I just started to build my replacement power supply connection as quickly as possible, without waiting for parts to be delivered. In addition I have a "space problem" at the left side of the chassis (where the original power supply and the 16x2 connector are located), as I mounted my ATX power supply exactly at this location. Therefore it is more convenient for me to have all connector pins at other locations of the backplane (giving me access any time without removing the power supply). The PC power supply is just small enough to fit into the Alphatronic case without any further modifications ;-).

    Is it a regular ATX? Maybe a micro ATX could free you some space there... But I imagine that's too much. :D

    For now relying on ATX is fine, fut I fear that soon the -12V signal will be removed from the standard, just as -5V was some time ago.

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Quote from Joe_IBM

    What about fixing the original PSU? If it kills the fuse immediately there must be a serious shortage that you can find with a multimeter. Do you have the schematics of the PSU?


    Best regards, Jochen

    I'm not that sure. What if there is some shortage in the transformer primary coil for instance? The cable coating can be damaged after all these years and I guess that would blow the fuse. I don't think it could be detected with the multimeter… On the other hand, it seems that most components are difficult to find nowadays. Lastly, since my Alphatronic is suffering other issues (it didn't work also before the power supply broke), I would prefer to ensure that the power is not an issue. And them try to check long term options for the power.


    I don't think I have the schematics. But maybe they are available somewhere. It has for sure a massive transformer that will be expensive for sure, if it is even available.


    When I can handle that issue, maybe I just disconnect the transformer secondary side, to see if it keeps blowing the fuse.


    There are also another replacement options. I remember to have bought one for my Colecovision that IIRC provides +5, +12, -12 (or maybe it was -5,...) but probably would not provide enough juice for the Alphatronic.


    Do we know how much power does the Alphatronic demands (fully loaded with cards and two disk drives) for each of the three power rails?


    Thanks and best regards

    Quote from gpospi

    Yes finally I would also consider using a 16x2 connector or a proper 32x3 connector. I just started to build my replacement power supply connection as quickly as possible, without waiting for parts to be delivered. In addition I have a "space problem" at the left side of the chassis (where the original power supply and the 16x2 connector are located), as I mounted my ATX power supply exactly at this location. Therefore it is more convenient for me to have all connector pins at other locations of the backplane (giving me access any time without removing the power supply). The PC power supply is just small enough to fit into the Alphatronic case without any further modifications ;-).

    Or even desoldering the backplane power sockets and replace them with some other connector. We would just need to find a 2x5 connector that suits (if I'm not mistaken) to drive all the power to the backplane.

    Quote from overCLK
    Quote from gpospi

    Yes finally I would also consider using a 16x2 connector or a proper 32x3 connector. I just started to build my replacement power supply connection as quickly as possible, without waiting for parts to be delivered. In addition I have a "space problem" at the left side of the chassis (where the original power supply and the 16x2 connector are located), as I mounted my ATX power supply exactly at this location. Therefore it is more convenient for me to have all connector pins at other locations of the backplane (giving me access any time without removing the power supply). The PC power supply is just small enough to fit into the Alphatronic case without any further modifications ;-).

    Or even desoldering the backplane power sockets and replace them with some other connector. We would just need to find a 2x5 connector that suits (if I'm not mistaken) to drive all the power to the backplane.

    I think it'd be better in this case to build an adaptor to ATX... But the idea of a native ATX backplane it's something I've been thinking in the past few months. There's also the additional "power-on" signal that should be cared of.


    A nearly-unrelated and maybe silly question: does anybody know of the two reset signals on the backplane, which one is fed into the 8085 and which is produced by it?

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Quote from Joe_IBM

    What about fixing the original PSU? If it kills the fuse immediately there must be a serious shortage that you can find with a multimeter. Do you have the schematics of the PSU?


    Best regards, Jochen

    That would be the ideal case, but not everybody is qualified enough to repair PSUs. Also, a poorly made repair could cause further damage to itself and maybe to the rest of the machine too.


    There's a factor of reliability too. We may (or not) rely on 40-year-old ics, but with a PSU... I think it's more reliable to replace it than to repair it. And if the ATX dies, the only needed thing to do is to replace it (unless its capacitors explode, then it's better to clean before :)).

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    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:


    Code
    Reset
CAAP-2500-3000

$1976 4010 40FF

.2
.2
…


    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. :)

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

    I heard that the keyboard controller sends some signals to the display controller, but don't know whose are are sent :fp:.

    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...

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Quote from jlopez

    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:

    Quote from jlopez

    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.

    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").

    I like this system, is one of my favourites. However, I haven't used it very much for fear of breaking it (more than it was). I don't know what the issue is, but I'm glad you localized (more or less) where it is. Let's wait until helwie44 † makes some statement. I'm sure he may have some idea of what's going wrong.

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Quote from gpospi

    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").

    Whoops. It's true. Your 48K are not recognized. Were you testing the computer with the memory board or without it? That's the same reset message I got when Elephant failed...

    When I tried to list all retro systems I have at home, the "The message is too long, must be under 500 characters" error appears! :lol:

    Quote from gpospi

    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. :)


    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).

    Edited once, last by gpospi ().

    Quote from gpospi

    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…

    Hallo overCLK , gpospi , jlopez und alle P2 USER.


    Leider habe ich im Moment wenig Zeit - aber die Beiträge zuvor - habe ich gelesen.


    Wenn eine P2 eingeschaltet wird (POWER ON) sollte ein RESET auf den BUS gesendet werden. Das wird mit einem RC und/oder Gatter (IC-TEil) einige „milli sekunden“ erzeugt.

    Damit wird über das MOS (CPU-RUN startet bei 0000h) der Ablauf wie in meiner PDF wie overCLK schon gelesen hatte.


    Es kann aber mal vorkommen, dass diese POWER-RESET Schaltung nicht geht. Genau wie auch mal (selten) bei meiner P2U (alles Original von 1982 TA im Betrieb) der Bildschirm ist dunkel und dann drücke ich einfach die Reset-Taste vom Keyboard - und sofort die RESET Anzeige und eine kurze Zeit (Speichertests) erfolgt unbedingt über den Buzzer ( auf der Key-Controller-Card) der akustischer BELL. Dann die EPROM Signaturen und der weiteren Speicher-Werte. Daher wird über die Reset Taste ein Zeitglied (Key-Controller-Card) auch ein RESET Signal auf den BUS gesendet.


    Dann sollte der „Prompt“ mit dem . (Punkt) erscheinen.


    Mit dem laufenden . (Punkt) und oder beliebiges Zeichen auf dem Display - deute so wie keine eingesteckte KEY-CONTROLLER-CARD und/oder ein fehlerhafte Bauteile auf der CARD?


    Ich melde mich .. später, soweit ich mehr Zeit habe.