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Thread: Ibm pc at parity check

  1. #31

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    I swapped out the system board and it seems to be working fine, however it only detects 2048K when it counts instead of the usual 2560K. Any ideas why? It’s not too much of an issue but I’d prefer to have that little bit of extra RAM.

    EDIT: Even with new RAM, a new motherboard, new ROMs, and only the essential cards required for running the PC, the error still occurs. Is this even possible? Could it be the FDD controller? The processor? One of the drives somehow? This is basically a new computer now. I could get a new 80286 off of eBay if I need to, but is it even possible that that is the issue? I’m pretty sure that it could possibly be the hard drive. I have another CMI 6426 that I could test with, but it doesn’t have any software and drivers I need. If that’s the issue I could do that painstakingly slow process of moving files by floppy disk.
    Last edited by jacobtohahn; May 23rd, 2018 at 05:04 PM.

  2. #32
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    Quote Originally Posted by jacobtohahn View Post
    EDIT: Even with new RAM, a new motherboard, new ROMs, and only the essential cards required for running the PC, the error still occurs. Is this even possible?
    * Maybe I missed it, but I cannot see anything in the previous threads where a different power supply was tried.
    * Flakey house power !
    * Air conditioner kicking in and out !

  3. Default

    Hi

    I'd bet that you don't have a hardware fault, but instead your PC is haunted by a very common boot sector virus, which will at seemingly random intervals display the message PARITY CHECK in 40 column mode and hang the machine. It is called Parity Boot, was very common in the early to mid 90s. As it is a boot sector virus, it spreads to any floppy accessed by the infected machine. I got Parity Boot multiple times, back then we used F-PROT to detect it. Removal is simple, just boot from a known clean floppy and rewrite the MBR of the hard disk with the command FDISK /MBR. Floppies can be cleaned with F-PROT.

  4. Default

    Remember to scan and disinfect all the floppies you ever inserted into this machine, and other machines you used these floppies in. The Parity Boot virus will stick to you like glue, trust me... I still found infected floppies decades after having the first Parity Boot infection.

    For a quick test: Boot the machine from a known clean and write protected DOS boot floppy. You shouldn't receive the PARITY CHECK message anymore. You could even take a look at the boot sector of the hard disk with Norton Disk Editor while working from a clean boot floppy and see the virus itself. Probably won't work when the computer is booted from an infected medium - if I remember correctly, the virus will hide any changes to the bootsector and just deliver an intact original boot sector when it is active.

  5. Default

    Quote Originally Posted by modem7 View Post
    * Maybe I missed it, but I cannot see anything in the previous threads where a different power supply was tried.
    * Flakey house power !
    * Air conditioner kicking in and out !
    I have an extra UPS that I can try. The power here usually seems fine though. Also, about the motherboard only detecting 2048K, is there a solution to that? I would like to avoid swapping the motherboard, as doing so increases the chances of me damaging the RAM chips or the board itself. Also, I believe that this board is newer because the chips are dated later and the board looks cleaner. The old board’s PCB is orangeish-brown (not from corrosion) while the newer one is green.

    Quote Originally Posted by diskettenfett View Post
    Remember to scan and disinfect all the floppies you ever inserted into this machine, and other machines you used these floppies in. The Parity Boot virus will stick to you like glue, trust me... I still found infected floppies decades after having the first Parity Boot infection.

    For a quick test: Boot the machine from a known clean and write protected DOS boot floppy. You shouldn't receive the PARITY CHECK message anymore. You could even take a look at the boot sector of the hard disk with Norton Disk Editor while working from a clean boot floppy and see the virus itself. Probably won't work when the computer is booted from an infected medium - if I remember correctly, the virus will hide any changes to the bootsector and just deliver an intact original boot sector when it is active.
    I’ll definitely try that on Monday, traveling this weekend. Pretty sure that is the issue, as the symptoms sound exactly like what I have.

  6. #36
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    Quote Originally Posted by jacobtohahn View Post
    Pretty sure that is the issue, as the symptoms sound exactly like what I have.
    It would certainly explain the lack of 'PARITY CHECK 1' or 'PARITY CHECK 2'.

    I have never encountered the subject virus before. Why didn't they make it more convincing by displaying, 'PARITY CHECK 1'.

  7. #37
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    Quote Originally Posted by jacobtohahn View Post
    Also, about the motherboard only detecting 2048K, is there a solution to that?
    No error message from the POST ?

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