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Thread: IBM 5150 won't run with 8087 fitted

  1. #1
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    Default IBM 5150 won't run with 8087 fitted

    I picked up an 8087 for my IBM 5150 since it was going cheap. Supposedly this is a NOS part but I have my doubts.

    With the copro fitted the system doesn't run - not even any sync on the display. Once taken out it runs fine. I do have position 2 on SW1 set to off as per minuszerodegrees.

    The original 8088 CPU was replaced with a V20 last year but I didn't expect that to make any difference.

    Anything I'm missing before sending back the 8087?

  2. #2

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    Did you try replacing the V20 with the 8088?
    Daniel P. Cayea - The Lyon Mountain Company - Plattsburgh, New York 12901
    Vintage Equipment: IBM 5150 * IBM 5161 * ThinkPad 770ED
    Modern Equipment: MacBook Pro 13 * Alienware M15R3

  3. #3
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    Quote Originally Posted by lyonadmiral View Post
    Did you try replacing the V20 with the 8088?
    Just dug out the 8088, made no difference.

  4. #4

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    Probably just a bad chip, return it

  5. #5
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    Default

    I assume you have followed the information here?

    5 MHz part or faster and changed the link/switch.

    Dave

  6. #6
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    Before you return it, post a close-up detailed picture of the chip -- would be curious to see if it's a fake or not.
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  7. #7
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    It's an 8087-1 which should be 10Mhz. The switch is set correctly (although makes no difference what position the switch is in - just having the chip installed stops the system from running in any way). Pics below, would welcome opinion on whether it's a fake or not. Certainly it looks real enough, it's in a real ceramic package at least.
    8087 top.jpg
    8087 bottom.jpg

  8. #8
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    My opinion is that it is fake or counterfeit; the type D ceramic packages had a copyright year on them of 1980, not 1978 (at least the ones I've seen, verified by George Phillips' guide). The lettering also isn't quite the same as the other D8087-1s I've seen.

    I'd get another D8087-1 that looks different from the one you have (with a copyright year of 1980) and see if that works.
    Offering a bounty for:
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  9. #9
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    I thought the 8087 was announced/launched in 1980 too. The 8086 was launched in 1978.

    I was looking through some of my old Intel data books. The one from 1980 doesn't even list the 8087 in the 8086 etc. section. The later edition I have does.

    I also suspect that what you have is a fake - or two 8086 chips (one labelled as an 8087)!

    Dave

  10. #10

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    Quote Originally Posted by Trixter View Post
    The lettering also isn't quite the same as the other D8087-1s I've seen.
    Yep, there's something about the above photo that "just doesn't look quite right" (such as the spacing between characters). And I'd suspect (even if NOS), the lettering on it would be more worn/faded after approx. 40 years.
    Last edited by T-R-A; June 12th, 2020 at 02:57 PM.

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