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Thread: AT&T PC 6300/M24 video controller disable

  1. #1

    Default AT&T PC 6300/M24 video controller disable

    Hi,

    I am restoring an Olivetti M24. I would like to disable the video card and put a VGA ISA card.

    There are 3 requirements:

    1) BIOS 1.43
    2) Set pins 5 and 6 on DIPSW-1 on the motherboard to ON
    3) Configure the new VGA card to 8 bit mode, it using a 16 bit ISA card

    But it seems that is not all. The video card needs to be disabled too. In some cases this card in Olivetti M24 comes with switches W1, W2, W3. My card is "GO318" and it does not have these switches (see attached). It looks like model P8 from 1984. On wikipedia there is some section that says there needs to be a modification done on the card to disabled it.

    So I found the procedure (see attached). I believe. I have also attached a picture of the chip that is supposed to be removed (in red).

    My question is: did somebody ever tried this? Does it look like the correct procedure to disable the card (in the case of missing W1,W2,W3 switches)?
    Attached Images Attached Images

  2. #2
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    I did try this, and it didn’t work. But then again - the proprietary video card is one of the nice quirks of these machines, why would you want to put a VGA card in? If you don’t have an original monitor, a simple adaptor can be built to use some (cheaply available) older VGA LCD monitors.

  3. #3
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    If you check my blog on PAL cloning, you'll see that the way a previous owner disabled the video on my (used to have) PC 6300, was to simply remove a socketed PAL. Easy and it works--but don't lose the PAL.

  4. #4

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    You mean you did desolder the chip, but that did not disabled the card?
    But then the problem could have been the VGA video card for example (not being compatible) ... or something else.

  5. #5
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    Indeed, I cannot completely rule out that the problem was with the VGA card. I know the card I used works and I know it works in an 8-bit ISA slot of a 486 motherboard, but I cannot rule out that its bios uses 186+ instructions and hence that could be why it did not work in the AT&T 6300. Anyway, I soon lost interest in this conversion since as I said I quite like the original video modes of the 6300. Also it’s literally cheaper just to buy a compatible LCD monitor than a true 8-bit compatible VGA card - the NEC 1990FXp sells on eBay for $25 delivered!

    https://www.ebay.com/itm/NEC-MultiSy...pid=1180198869

  6. #6
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    Quote Originally Posted by Valerio View Post
    the NEC 1990FXp sells on eBay for $25 delivered!
    Yes, those are like swiss army knifes of TFT monitors for classic computers.

  7. #7
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    On my system, the PALs are in sockets, so it's just a matter of removing the chip. This disables all of the address decoding for the integrated display controller--i.e., the system acts as if it's no longer there.

    I used a Tsenglabs ET4000 16-bit VGA card in 8 bit mode.

  8. #8
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    Slightly off topic, but since we are in the ballpark: I have an M24-rebranded AT&T PC 6300 which, the last time I powered it on had trouble with video sync; i.e. the BIOS boot communications would be legible, but in the wrong place. For example the "C:" prompt might wind up in column 13 or 45, or wrap part of a line. Today the display, which is the monochrome unit powered by the video card, would not sync at all. Video appears to have lost horizontal synchronization altogether.

    I also have an AT&T 6312 WGS which has a color display that thankfully is working at the moment. So the question here is: Can I swap monitors as a quick check to determine whether the 6300's sync problem is with the card or the monitor? The two CRTs have the same DSUB connector but a different pin count, and the 6312 display has a separate power cord (and on/off switch) whereas the 6300 display has neither, getting its power from the display card.

    No point in frying anything, so I thought I might ask the brain-trust. Thanks for your replies.

    -CH-

  9. #9
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    AT&T 6312 WGSis the same as M240? Then yes, you can do so.

  10. #10
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    Thank you for your reply. As I have the 6300 stripped down at the moment in order to inspect the video card (Chuck's advice: unseat and reseat everything) I will try the monochrome monitor on the 6312 long enough to see if it syncs.

    -CH-

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