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Thread: Compaq Portable I Lo-Tech ISA XT CF adapter boot issues

  1. #1

    Default Compaq Portable I Lo-Tech ISA XT CF adapter boot issues

    Got around to trying to install a Lo-Tech ISA XT CF adapter in my Compaq Portable. Experiencing some very strange results. Occasionally when I power it on it will successfully boot off the CF card. Most of the time the motherboard power light lights briefly and then goes out. If I power cycle it it will continue to light only briefly. If I pull the Lo-tech card out it will immediately power up and boot off a floppy just fine. I have tested the CF card in my 5170 and it boots up fine with no issues. If I let it sit for an extended period of time it will again boot, but only once before it starts the immediate shutdown routine when power cycled. Any thoughts on what might be going on? Anyone else using a Lo-tech CF card in there Compaq portable??

    I would try the lo-tech card in another XT class machine but I don't have one. Thanks, Chris

  2. #2
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    Hmm... That sounds like a combination of a weak power supply on the Compaq and a wonky capacitor on the Lo-Tech. If you let it sit, the capacitor discharges and and it looks like a normal draw on the power supply on power up. If you "power cycle", the capacitor on the lo-tech is still charged during power up and looks like a short or high current draw and the power supply shuts down. Have you checked the output volts on the PSU? Others here can lead you to some better diags than I can. Just thought I'd put in my one cent worth so that this thread stays visible.

    Greg

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    I +1 on the previous that it almost must be something on the card that at least intermittently looks like a short. Did you assemble the card yourself or buy it pre-built? I'd probably start looking at the electrolytic cap(s) and making sure the polarity is correct.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  4. #4

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    I purchased the card already assembled from TelElec last time I bought some keyboard foams.

    What would cause the power supply to be week? Aging filter caps? I have two compaq portables and it behaves the same in both of them.

    The PCB isn't silk screened that I can see, perhaps its under the capacitor. Guess I will pull the cap off an take a look.

  5. #5

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    removed the orientation specific capacitors (1 electrolytic and 1 tantalum) No change. Powers up first time only. Won't on power cycle till I remove the card.

    From what I can tell they were both correctly oriented related to the silk screen. Guess the silk screen could be wrong. either way with them removed the problem still remains.

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    Quote Originally Posted by acenewman View Post
    What would cause the power supply to be week? Aging filter caps? I have two compaq portables and it behaves the same in both of them.
    That is very weird. Electrolytic capacitors in power supplies can slowly go bad in such a way that the supply puts out less and less power, often causing non-obvious intermittent problems. But I would not expect two units to be at the exact same level of failure.

    What exactly do you have attached to the XT CF? Does the problem occur if there is nothing attached to the XT CF?

    Can you verify that the contacts on the card line up 100% with the ISA slot? Sometimes things don't always fit properly.

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    Which XT-CF card do you have? Is it the one with the CF slot built onto the card, or is it the one with the 40 pin IDE connector that takes an external adapter? If it’s the latter, I wonder if your adapter could be cross-shorting the power-on-pin 20 feature.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  8. #8

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    I have the card without the integrated card interface. If behaves the same even when I have no cable or card attached to the interface.

  9. #9
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    That is genuinely puzzling. That card should draw very little power (in the grand scheme of things) and it frankly just isn't that complicated.

    This is an out-of-left-field suggestion: There's a jumper on those cards for PC-XT slot 8 enable; anything change if you change the state of that jumper?
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  10. #10

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    works only when the slot 8 jumper is set for slot 8 use. when not set for slot 8 it gives a disk access error message.

    still has the issue with tripping the supply if the slot 8 jumper is used.

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