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Commodore Plus 4 tot (nicht von TED oder CPU)

  • Hallo. Es tut mir leid für meine Übersetzung, aber ich kann kein Deutsch, also habe ich Google Übersetzer verwendet.Ich kaufte vor kurzem Plus 4 von eBay als nicht funktionierend (mit umgedrehtem TED / CPU in den Sockeln - ich habe es nicht so angeschlossen). Ich habe CPU und TED auf einem anderen Rechner geprüft - beide tot. Also habe ich funktionierende CPU / TED von einer anderen Maschine auf diese gesetzt, die C64-Steckdose gelötet (war vorher quadratisch) und Plus 4 lief nicht.Es zeigt die ganze Zeit einen schwarzen Bildschirm.Was ich sonst gemacht habe:
    0. Kondensator geändert
    1. Geprüfte Spannung - + 5 V an der CPU-Leitung
    2. Geprüft auf kurze Masse bis 5V - nicht kurz - nur ca. 300ohm zwischen ihnen
    3. Geprüfte Lum-Signale nur von TEDs Pin 23 an TV - noch schwarzer Bildschirm (zum Vergleich: Mein C16 zeigt blasses Schwarzweißbild auf diesem Pin)
    4. Alle Speicherchips für 4164 geändert
    5. Geändert: U23, U24, U25, U19 von einer anderen Arbeitsmaschine
    6. Setzen Sie neue 74LS139, 74LS257 (beide) ein.
    7. Kristall in der Nähe von TED mit anderen Funktionen geprüft
    8. Geprüfter Reset (Schalter, IC 555 Swap, IC 7406 tauschen)
    Und ich habe aufgegeben ... Immer noch schwarzer Bildschirm. Kann jemand helfen, was kann ich mehr prüfen?

  • PLA - yes, I took it from working C16, and checked this one from dead Plus 4 on C16 as well - on C16 both PLA chips run.

    U7 used for IEC and the Reset-circuit may tear down the CPU. Toggles the logic level by pressing reset at the CPU ?


    U7 - well, I have change this chip also before, as I suspected it was dead. So with new chip, when I messure voltage between CPU 40 (reset) and ground line - it shows 5V, when I press reset button, then it shows low state (ca. 150mV). What else can I check with reset line?

  • If you've got an EPROM programmer burn the "DIAG264" into an EPROM and replace the kernal with it. It should run even with no RAM available. However, CPU, TED and PLA must be OK for this - if they are and DIAG264 still doesn't run there is likely something blocking the address or data bus. I'd pull out any ROM anyway before running DIAG264, ROMs are often found to be "bus blockers".


    See http://inchocks.co.uk/commodor…64/HTMLManual/Diag264.htm for details.

  • Please re-check CPU and TED in the machine you took them from - just to make sure the board has not destroyed them yet.

    I have checked it - they still work :) I also tried with 8500 CPU adapter + special kernal, as well as with 7501.

    If you've got an EPROM programmer burn the "DIAG264" into an EPROM and replace the kernal with it. It should run even with no RAM available. However, CPU, TED and PLA must be OK for this - if they are and DIAG264 still doesn't run there is likely something blocking the address or data bus. I'd pull out any ROM anyway before running DIAG264, ROMs are often found to be "bus blockers".


    See http://inchocks.co.uk/commodor…64/HTMLManual/Diag264.htm for details.

    I do not have it, I need to borrow it then. Will 264 diag from TFW8B will work like this as well?


    You mentioned data/adress bus could be problem. Maybe I check all those traces by mulimeter then?

  • You mentioned data/adress bus could be problem. Maybe I check all those traces by mulimeter then?

    Yes, you might check the address and data bus traces between the components with a multimeter. You could also check the address and data bus lines for short circuits to VCC or GND or for shorts between the bus lines, although I wouldn't recommend that. An oscilloscope would be the tool of choice for that.


    I would opt for the DIAG264 solution since it is less invasive than a multimeter in ohms mode.

    Will 264 diag from TFW8B will work like this as well?

    DIAG264 was developed by Rob Clarke ("crock"). I'm only aware of his version (see the website in my post above) and can't say something about others. (It seems a lot of people are using Rob's work to gain additional $$ with minimal input on eBay and other places.) I've never heard of TFW8B's work and can't say anything about it.

  • Will 264 diag from TFW8B will work like this as well?

    OK, had a qucik look at https://www.thefuturewas8bit.com/diag-264.html ...


    Rob developed two different ROMs:


    One to place directly in the KERNAL socket - this one will boot even if the expansion port is damaged, RAM faulty etc., as long as the CPU is able to access the KERNAL ROM and read the RESET vector. This one will report bad RAMs by blinking and/or displaying characters on the screen. It does not need any stack or zero page RAM to start and report damage.


    The second ROM is a cartridge ROM - it seems this is the version sold at TFW8B - it will only work if the original KERNAL is able to boot and start the cartridge ROM. Therefore at least stack and zeropage RAM has to be OK I guess, otherwise the kernal will crash I think and won't run the DIAG264 from cart. A cartridge version is quite handy although rather useless in dead testing, it is OK for testing ports etc. when the machine comes up.


    For a dead test I'd strongly recommend the KERNAL version.

  • Any chance that 6551 can cause this kind of damage?

    Sure, any device on the address or data bus can block it obviously, thus I have recommended to pull all ICs not needed for a startup earlier, If the 6551 is in a socket I'd pull it anyway until the machine runs.

  • 6551 is now in socket cause I desolder it. Pity that it is one of the chips I do not have spare for.

    On the other side it's not needed for most use cases. If I had to choose between TED, CPU and ACIA I'd certainly sacrifice ACIA :D ...


    Where are you from? I could provide you with a DIAG264 kernal EPROM to speed things up a bit if it takes a bunch of time for you to get hand on a programmer. Depends only on the shipping cost and delivery time I guess. If you are in need PM me via the board.

  • I am waiting fo diag264 (thanks to kinzi!), but in the mean time I made some very little progress.


    First I swap 8551 to eliminate it - it works on other Plus machine, so it is good.
    Second - I now use original CPU 8501 for testing my dead Plus 4 (somehow 8500+adapter would not work on other working Plus 4 machine - so maybe also on this one, even though it works on C16)
    Third - I connected directly 5VDC to board, using other modern PSU, 9VAC is not there now
    Forth - I have found one trace that could be problem and fixed it


    Now I have this (photo), or black screen again. But mostly black screen. Never the less, something appeared for the moment, so progress is there :)


    After I get diag I can make more tests, but maybe now it came more clear to somebody what can be wrong?

  • The characters don't look very clean. Does your current TED work 100 %?


    [OT]


    I've got a TED with clean picture at startup but garbeled screen running diag. It used to be working over years in my C16 test board and now suddenly shows this strange behaviour. I've got also a 8501 CPU which died slowly ... first the diag run but one bit was corrupt: Read from KERNAL/DIAG was obviously OK because the program ran but there seemed to be a problem when writing data since this bit always was set (or cleared, don't remember exactly). After several weeks in this state the CPU now even refuses to start with diag ... slow death I presume.


    [/OT]


    Thus your TED could also suffer from a partial problem.

    I now use original CPU 8501 for testing my dead Plus 4 (somehow 8500+adapter would not work on other working Plus 4 machine - so maybe also on this one, even though it works on C16)

    A 8500 with adapter runs in my C16 test board wirhout problems. I've never tested it in a PLUS/4 though but don't see why it shouldn't work. I even tested a 6510 and it works but becomes slightly warmer than the 8500.


    So when PLA was already ruled out and TED is OK it could be a RAM problem. What types of RAM chips does the PLUS/4 have, i. e. from which manufacturer?

  • TED is good for sure, but I think we have a winner!


    It was 6529B (the one above CPU).


    Never thought of this one, but somewhere I've found simple block schematics of Plus 4 which showed data bus with all chips involved. Also it was mentioned here, that if bus is blocked - the problem can be like mine. This is only chip I did not checked that is involved in bus line.


    I also was told lately by one of AA forum users, that 74LS245 can work as well, so I tried and it works, but only when you swap to the one above CPU, the other one, from what I understood, should have NOT gate (inverter should be used) on 19 leg, but I did not check it yet. If you use 74LS245 instead of 6529B near keyboard connection - keys do not work.


    Now Plus 4 works great! Thanks everybody for help.