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Thread: IBM early CGA in trouble

  1. #1

    Default IBM early CGA in trouble

    Ok next problem is CGA, its old 1981-82 type.
    System report one long and two short beeps, all what I get on monitors is this.

    48F57512-479C-43B9-A631-B9FDF236399E.jpg 83f12751922db284d805fa56cf2ba32f.jpg

    Tested was:

    RAM - all is OK
    main 6845 IC - OK
    ROM chip - OK

    So what is next step? Thanks
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
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  2. #2

    Default

    The computer boots fine with a different card installed?
    I have a Major in Post-Apocalyptic Economics.
    Wanted: Any PC-Compatible Reciprocation Dingle Arm

  3. #3

    Default

    yes, computer starts even with this card and boots normally, however you don's see anything of course
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
    My IBM PC hardware collection

  4. #4
    Join Date
    May 2006
    Location
    Melbourne, Australia
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    Default

    On my IBM MDA equipped IBM 5160, if I set the motherboard's two video switches to ON, then power on the 5160, I see a cursor appear. That tells me that without any programming/setup by the 5160's POST, the IBM MDA card is self initialising to a mode that is compatible with the IBM MDA monitor.

    If I repeat the same experiment on my IBM CGA equipped IBM 5160, I see that the IBM CGA monitor displays an un-synced raster. And looking at the horizontal and vertical sync pulses (shown at [here]) coming out of the CGA card, I can see why.
    The photo that you have provided shows a CGA screen that is synced, suggesting to me that the POST is at the least, able to program/setup the card for a CGA monitor.

    But the POST does more than just send commands to the CGA card to set a video mode. The source code for the POST shows that a test is done of the video RAM, and there is a 'CRT interface lines test'. Failure of either test will result in the '1 long beep then 2 short beeps' error.

  5. #5
    Join Date
    May 2006
    Location
    Melbourne, Australia
    Posts
    6,100

    Default

    Quote Originally Posted by modem7 View Post
    But the POST does more than just send commands to the CGA card to set a video mode. The source code for the POST shows that a test is done of the video RAM, and there is a 'CRT interface lines test'. Failure of either test will result in the '1 long beep then 2 short beeps' error.
    In my IBM MDA equipped IBM 5160, I simply added an IBM CGA card. Nothing else (e.g. video switches left set for MDA). Powered up the 5160. The POST output and DOS came up on the monochrome display as expected.

    At this point, per [here], the CGA card's RAM is exposed to the 5160 at B8000 (736K) through BBFFF (752K-1).

    I then ran CheckIt. I then selected the memory test, altering the 'Base Memory' range to be tested to 736K through 752K. I ran the test, and it passed.

    I then simulated a RAM chip failure by grounding pin 14 on one of the CGA card's RAM chips. As expected, a running of the same test with same parameters then failed.

    Of course, my test was not only of the CGA card's RAM chips. It was of both the RAM chips, and the supporting circuitry on the card that is required to read and write to the RAM chips.

  6. #6

    Default

    After some laboring and investigating, we have another picture decay

    1e7afd98c857b0b51715c4261a03d33e.jpg

    I don't know, its worst or better...
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
    My IBM PC hardware collection

  7. #7

    Default

    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
    My IBM PC hardware collection

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