zx spectrum 48k loading issue (memory problem i think)

edited February 2011 in Hardware
Hi

I have a 48k spectrum that until yesterday was working flawlessly.
The spectrum seems to work fine but the problem is with loading games.All the loading process, in most of the games, is normal , but when the audio from the cassette finishes usually the spectrum restarts by it self back to the start screen ( gray with 1982 Sinclair research ltd) or sometimes the screen turns black.in some games shows error codes like 4 - Out of Memory ; B - Integer out of range ; C - Nonsense in BASIC.
I know the games are fine cause they were tested a few days ago and i already tried with 9 different games.
I was advised to try loading 16k games and they seem to work fine.I was told that could be a memory problem.
Is there a way to find were the problem is?
I'm sorry to bother you with all this questions.

Here's a video of an exemple for what happened with Manic Miner:

http://www.youtube.com/watch?v=6hcs_IbYXOM

( don't know why the video is sideway )

Thank you in advance

Ricardo Gon?alves
Post edited by Trajano on

Comments

  • edited February 2011
    Trajano wrote: »
    I was advised to try loading 16k games and they seem to work fine.I was told that could be a memory problem.
    Is there a way to find were the problem is?

    Try PRINT PEEK 23733 immediately after switch-on. On a 48K Spectrum, it should give you 255 - anything less than that means that the startup memory test has found a fault.
  • edited February 2011
    gasman wrote: »
    Try PRINT PEEK 23733 immediately after switch-on. On a 48K Spectrum, it should give you 255 - anything less than that means that the startup memory test has found a fault.

    It gave me 255... that is supposed to be good but the games still don't load :(
    Is there another way to check for faults?
    May I should test something on the board with a multimeter?

    Thank you
  • edited February 2011
    Hi
    Trajano wrote: »
    It gave me 255... that is supposed to be good but the games still don't load :(
    Is there another way to check for faults?
    May I should test something on the board with a multimeter?

    Thank you

    check with the full command

    PRINT PEEK 23732 + PEEK 23733 * 256

    The value printed should be: 65535

    bye

    Jos? Leandro
  • edited February 2011
    Hi



    check with the full command

    PRINT PEEK 23732 + PEEK 23733 * 256

    The value printed should be: 65535

    bye

    Jos? Leandro

    It gave me that value...
    This were all memory tests?
    If the values are OK means the memorys are fine or can be related with some more serious issue?

    Thank you
  • edited February 2011
    Try repeating above command after the Spectrum has been on for a while (say, >20 mins or so) and it reset like described above. Perhaps there's an intermittent RAM fault that only occurs when the Spectrum heats up. :???:

    2nd option: run some RAM-test programs to test the RAM more extensively than the built-in check on bootup.
  • edited February 2011
    I just tried the above tests on an issue 3b speccy to try to identify lower or upper ram and im getting 128, and 32830. Running fruitcakes 128 memory diagnostic give me bad ram in data line 4, so if it is upper ram then it would be IC19, or if its lower, IC10, thats the thing, how to tell if its upper or lower, im missing something obvious as usual, anyone care to point out what that might be? (sorry about hijacking the thread btw)
  • edited February 2011
    Isn't all above 16384 in upper RAM then ?
  • edited February 2011
    Isn't all above 16384 in upper RAM then ?

    It is. Unfortunately it can be also bad data line. Check PCB, as I remember 3b has soldered DRAM. Otherwise you could just put 4164 chip in socket.
  • edited February 2011
    Thanks guys, im going to de-solder (what a pain!) and socket IC19 and continue in upper ram until I chase the fault off the board, just needed to know where to start!
  • edited February 2011
    Try repeating above command after the Spectrum has been on for a while (say, >20 mins or so) and it reset like described above. Perhaps there's an intermittent RAM fault that only occurs when the Spectrum heats up. :???:

    2nd option: run some RAM-test programs to test the RAM more extensively than the built-in check on bootup.

    The spectrum don't load the games even after i start using it.Although the numbers are correct on the built-in check it still don't load games :sad:
    How can I be sure that this is a memory problem and, if so, how can I know witch memory is damaged?

    Thank you
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