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Computer won't post with my favorite keyboard plugged in.

Discussion in 'Electronic Repair' started by mike, Jul 10, 2013.

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  1. mike

    mike Guest

    I have a XT/AT keyboard that I've used for 20 years with many machines.
    Works extremely well and the layout is what I want.

    Just upgraded to a HP Pavilion a6200n.
    The thing won't post with my favorite keyboard plugged in the PS/2
    socket. Just sits there with a black screen.

    Swapped keyboards and it works fine. But the keyboard sucks.
    I've got a bunch of keyboards and they all suck. Keys stick,
    keys in different locations. My old keyboard works just great.

    Any ideas on what I might try to get my old keyboard to work?
  2. Maybe your new machine does not provide the power required by the old

    As for the keycodes and the protocol, AFAIK they did not change.

    petrus bitbyter
  3. JW

    JW Guest

    If you can't get it to work in the PS/2 port, you could try a PS/2 to USB
    adapter. While I had nothing but problems with a Belkin one, I've had good
    luck with this one:
  4. The protocol changed from the original PC (and XT) to the PC/AT. Since then
    the protocol has not changed. The keycodes have had new ones added for various
    functions such as sleep, email, etc, but the regular a-z, 0-9, F1-12, etc have
    not changed since the introduction of the PC/AT.

    At one point the connector changed, with the wiring being to different
    pins, adaptors were easily available.

    USB keyboards use the same data, it's now encapsulated in USB data

  5. An XT/AT keyboard would have the older "DINnish" plug -- not a PS/2 plug. To
    the best of my knowledge, they are not compatible. (But I could be wrong,

    Why not replace it with a Unicomp "buckling spring" keyboard? That's what I
  6. Good idea to get a good one. I have many that were $2 each from China
    bought via eBay. They all worked (although not on MacOS) but seem to burn
    out after about a month.

    Windows recognized them with no trouble, some BIOSes did not recognize them
    at all, there was no keyboard support until the computer finished

    An Office Depot brand one, which cost $10, worked fine in all of those
    situations the cheap ones did not.

  7. Bob F

    Bob F Guest

  8. Bob F

    Bob F Guest

    I have a couple adapters that worked fine.
  9. mike

    mike Guest

    Thanks, guys for the input.
    I really don't want to buy yet another keyboard.
    If I can find one like this with the function keys down the side
    and the qwerty centered in the frame, it's likely to cost a fortune.

    I'm sure I could get used to this new keyboard...I just don't want to
    My fingers know how to drive this one.

    I've got usb adapters too. Had trouble with all of them...mostly
    with stuff that needed to be done before the system boots.

    This old keyboard has worked with many different PS/2 sockets over the

    Measuring the power consumption is on the todo list.

    I'd understand if it didn't work due to insufficient power.
    But it won't let the computer even POST.

    I'll have to make an adapter I can probe.

    I've also got several USB keyboards with built-in touchpads.
    They work well for a while, then just stop. Replugging the USB
    brings 'em back. I'd like to figger out what's wrong with them too.
    My workbench doesn't have any place to work a mouse.
  10. I've got one though on what your trouble might be:

    Way back sometime in the late 80s, early 90s I wrote the code for a few
    keyboard controllers used in clone PCs. Even though IBM had published a
    spec. on the timing that keyboards were supposed to meet, many of them
    didn't even come close. But they all worked with early PC hardware
    because all they were using was a hardware shift register that was
    tolerant of a lot of variation. When we used a micro processor (6502
    based and 8047(?)) I had to build in a test to try to identify aspects
    of the signal timing during POST and adapt to whatever keyboard was
    plugged in. I doubt they go through all that trouble anymore.

    You may get lucky and find a particular ps/2 to usb adapter that will

    If you're real ambitious you could program a PIC or Arduino or something
    to do the translation for you.

    I still have an old favorite keyboard from that era. But at this point,
    if it ever gave me problems, I think I would just finally toss it.
  11. My experience has been that, when I get involved restoring or repairing a
    favorite thing, it's not long afterward that "something happens" that makes me
    want to get rid of it or replace it.

    Obviously, individual reactions vary. But I warn the OP that this could
    happen, and his effort to adapt the fave keyboard could turn out to be a waste
    of time.
  12. They are exactly the same electrically, I have adaptors that connect
    PS/2 keyboards to AT style sockets and others that connect AT style keyboards
    to PS/2 sockets.

    The codes are the same, so you can buy a device that connects a PS/2
    keyboard to a USB port. If you have the right adaptor, you can connect
    an AT keyboard to it.

  13. Sjouke Burry

    Sjouke Burry Guest

    Is there an xt/at switch at the bottom of the keyboard?
    If so try both positions.
  14. That "Opps" is the reason that breaking a pin would be my very last option.
    It should not be that difficult to interrupt the reset line on a place and
    in a way it can be restored if necessary. Very unlikely? You just proved the
    opposite :)

    I too still have an XT/AT-keyboard that works fine so far. It can be
    switched between XT and AT. Differences are way to large for a simple
    solution. So the switch instructs the old 8048 to use completely different
    main program. But the HMOS version of the old 8048 is more powerhungry then
    the newer CMOS version. Still newer processors has all of the elctronics
    stuffed inside (except for the LEDs) and requires way less power.

    petrus bitbyter
  15. That's simple then. Grab a female connector that matches the keyboard,
    grab a male connector that matches the computer, and wire them up, leaving
    off the reset line.

    Or most keyboards, the cable plugs into a connector inside. So it's easy
    to cut the wire there. Indeed, at one point I needed a small connector
    keyboard and didn't have a suitable one, so I was going to take a cable I
    did have that had the small connector and use it rather than the
    keyboard's original cable.

    If the keyboard really is drawing too much current, then clearly something
    in the computer is between the +5v line and where the keyboard plugs in.
    So bypassing that whatever would fix it, if this is the problem.

  16. Guest

    I've had only one motherboard do that, but I don't remember which
    one or which keyboard. Every other motherboard I tried that was
    incompatible caused a "keyboard error press F1 to continue" error

    Even if your XT/AT keyboard is designed to automatically select
    XT or AT mode, it may have a jumper inside to set the default
    mode, or its circuit board may be laid out for a manual XT/AT
    mode selector switch that was needed by an older version of the
    firmware. Sometimes you can select the default by soldering a
    wire between the copper pad meant for the center terminal of the
    missing switch and one of its other copper pads. Doing that made
    a couple of my keyboards compatible with certain motherboards, yet
    the auto-select still worked, but with other keyboards it didn't help
    at all. If you feel that installing such a wire could short and damage
    something, use a 200-300 ohm resistor instead.

    Places like and have lots of information
    about keyboards, including some schematics at the latter.
  17. Guest

    I forgot to mention: another thing that might help is changing the value
    of any power-on reset capacitor, especially if your keyboard works
    when you hit the hardware reset button on your computer.
  18. If you modify that brandnew machine you will loose all guarantee.

    First thing to do is making a breakout cable and measuring the power and
    reset lines using a voltage meter. Especially looking for differences
    between the old and the new keyboard. Clock and data lines are important as
    well but a voltage meter may not do. An o'scope will... If only you have

    There's one much more complex possibility for the cause of the problem:
    Noise from the keyboard. Some of that older keyboards are a little bit noisy
    and maybe the new machines inputs are to sensible. Fighting this problem
    requires some filtering which in turn requires experience and experiments.
    There's no general prescription for it.

    One thing can be tried easily however: Some ferrite clamp(s) on the keyboard
    cable. If the keyboard is radiating noise *and* if that noise is picked up
    by the cable *and* if the computers input(s) cannot handle it *then* you
    have a good chance to fix the problem with it. Conducted noise cannot be
    fought this way.

    petrus bitbyter
  19. "dave" wrote in message
    Adding or changing cards or peripherals? Yes. Altering the wiring? I doubt it.
  20. The last "new" computer I bought was in 1989, so when I saw "new" I was
    thinking it was actually a used computer new to the poster.

    No, bypassing whatever current limiting there might be between the +5v
    line and the keyboard is likely going to cause issues with warranty. Of
    course, that only matters if you need the warranty, ie the computer fails
    and you want to send it back.

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