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Thread: Apple II Clone Keeps Repeating Keys - Help?

  1. #1

    Unhappy Apple II Clone Keeps Repeating Keys - Help?

    Hey all,

    I bought a Japanese Apple II clone recently and am in the process of restoring it. It appears to have a dead power supply, so I've rigged a PC/AT PSU for the time being and sure enough it powers on to the Apple ][ prompt. Everything seemed to be working at first... until I hit "Shift" + "/" to get a question mark, at which point the computer started beeping rather rapidly and filling the screen with a combination of "?" and "/" line by line. Sometimes when this happens, the backgrounds of the characters are coloured too. Hitting Return stops it, and hitting the "/" key without shift works fine. It also happens with some other symbols such as ">", but it doesn't happen with every Shift-modifiable symbol key - every alphabetical and top-row number key works fine with and without Shift.

    I tried removing each logic and rom chip, dusting them and their sockets, and reinserting them but nothing changed. I also tried doing the same to the two chips on the keyboard PCB but still no change.

    Here's a photo of the problem: https://i.imgur.com/QTMXTFH.jpg

    I'm 99% sure the weird colour bleeding/artifacting/whatever is due to the cable I'm using. This clone has a 3.5mm headphone jack for video, and the cable it came with is fairly old and stiff, so it should probably be ignored unless you think it might be related to this key repetition problem.

    Also, it occasionally starts spewing question marks immediately on boot until I hit enter, but this isn't a consistent problem like the one I described above.

    So, any ideas? Could the rom chips be failing, or is it maybe a memory problem? How would I go about diagnosing this? It might be worth mentioning that I have a Spectrum Micro Engenho 2 (Brazilian II+/IIe clone) that I could try stealing the chips from to test things, but I haven't confirmed that it even works since the internal power transformer is dead (another thing I need help with! But this Japanese clone comes first ).

    Thanks!

  2. #2

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    My IIe platinum would repeat key-presses, but just occasionally, and just certain keys. In my case, the switches are just dirty. I was able to just work the keys a bit and most behave now. Eventually I'll pop all of the caps off and hose down the switches with deox-it. Supposedly this is a pretty common issue. When I was googling it, another common issue was the keyboard encoder IC.

  3. #3
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    The problem is not in the keyboard.

    It's maybe a stuck /IRQ. But someone more familiar with Apple ][ theory of operation will likely know right away what it really is.

  4. #4
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    It is a little odd that only certain keys cause this. I'd examine the key switches first.

    But a seemingly common mode of failure involves the chips associated with the keyboard "strobe" line. Apple II/II+ and clone style keyboards usually connect via a DIN socket. This includes lines for power, ground, parallel data lines, and a strobe. The when a key is pressed, the keyboard asserts the ASCII value of the key pressed in parallel on the data lines and then signals a "strobe" to indicate that the value is ready to be read.

    Unfortunately, if the DIN connector is ever plugged in backwards the power gets connected to the strobe line and can damage it. The end result is often that all keys repeat (or no keys register at all). Partial damage can also result in intermittent repeating behavior - I had a keyboard that was doing something sort of similar a while back.

    Anyway, if it is not the key switches, I'd check along the strobe line. Both the chip on the motherboard, the chip on the keyboard controller, and the cable itself.

  5. #5
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    Because it is only a few keys that do it it is unlikely to be the keyboard strobe/clear logic.
    It is most likely to be a keyboard problem. Without knowing what type of clone keyboard it is, guessing the cause it a bit of a stab in the dark because the implementations vary quite a bit.
    However given that most keys are fine but a some keys that are probably grouped on a single scanline as the issue I would look for a dry joint at the keyboard controller/ROM decider or the pullup resistor.

  6. #6

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    Thanks all, I'll try cleaning the keyswitches and reflowing each solder joint first then.

  7. #7

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    I'm wondering what connector the clone board has for power? Why are you using a AT power supply and not the original? or another Apple ][ PS.
    I would want to start with known good power first then go from there.

  8. #8

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    The original power supply is dead, it was quicker for me to use an AT power supply than diagnose the old one - that comes later. The power is good, I highly doubt that's the problem.

    In other news, I tried reflowing the solder on each switch and nothing changed. I also tried triggering the problem and then disconnecting the keyboard, and it continued (aka. the question marks kept scrolling across the screen). But now there's a new problem: I tried reseating all of the chips again and discovered that a few of them had broken legs, but even after bridging the connections between what's left of those legs and the socket, the computer now boots to a solid screen full of question marks. I neglected to mention before, but this is essentially what I got when I turned the machine on for the first time but it had some flashing squares amidst the question marks back then.

    I've tried removing each chip and cleaning their pins to no avail (some required a bit of scraping).

  9. #9

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    There is a guy posting youtube videos where he is trying to repair a computer for a kid on a facebook group. It had the same screen full of question marks. Here is episode 2 that shows it: https://www.youtube.com/watch?v=IqDtOv8kDrU

  10. #10
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    Quote Originally Posted by Joudan View Post
    In other news, I tried reflowing the solder on each switch and nothing changed. I also tried triggering the problem and then disconnecting the keyboard, and it continued (aka. the question marks kept scrolling across the screen). But now there's a new problem: I tried reseating all of the chips again and discovered that a few of them had broken legs, but even after bridging the connections between what's left of those legs and the socket, the computer now boots to a solid screen full of question marks. I neglected to mention before, but this is essentially what I got when I turned the machine on for the first time but it had some flashing squares amidst the question marks back then.

    I've tried removing each chip and cleaning their pins to no avail (some required a bit of scraping).
    Powering on with a screen full of question marks is a completely different scenario than a screen filling with question marks after pressing a key.
    You need to be really clear on the fault description for advice to be good enough to be of any help.

    Did the fault change after you reseated the chips or did it always have a screen full of question marks at power on?
    Does it power on normally without question marks with the keyboard unplugged?
    Does it power on normally without question marks with the keyboard plugged in and olny starts generating question marks after you press the "?/" key?

    Also when I suggested the reflow, the problem is more likely on the scanlines and the associated pull up resistors not the individual keys. Posting a photo of the chips on the keyboard will allow me to point you at the chips most likely to be the problem.
    Due to the inaccurate description of the fault you probably should expand your fault search and check the mainboard IC's at B5, B6, A12 and C11
    Last edited by David_M; September 13th, 2018 at 12:35 PM.

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