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Thread: Sol20 keyboard issue

  1. #11
    Join Date
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    Quote Originally Posted by falter View Post
    When I last bought pads from another seller they were a lighter density green foam with mylar and they work awesome.
    Those were closer to the material KT originally used. You really want to use low-density polyethane foam instead of the polyurethane so they won't crumble over time, but
    it is difficult to find. The main difference will be key travel and force required to actuate a key. I've made hundreds of them, an example is on the left here:
    pad.JPG
    Higher density, but the same thickness as the originals.

    see:
    https://groups.google.com/forum/#!to...st/ki86xMT7gww
    "Making perfect Keytronic replacement keypads"
    Last edited by Al Kossow; June 22nd, 2018 at 08:51 AM.

  2. #12
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    I've done a ton of checking around and still not sure what's going on.

    I've removed and cleaned every IC on the thing, with no change in behavior. I've tried swapping ICs with known good, and testing the existing in other machines. No problem. I've checked every IC pin connection to the PCB (from top of chip leg to where the socket leg is soldered in). No problem.

    One strange aspect is no matter how long you run the Sol for after the keyboard starts working (usually about 5-10 minutes), if you shut it off even for 10 seconds and then power back on.. you're back to square one. I would have thought if it was a cold solder problem or a component that only makes proper contact after being heated up, that it'd still work after a quick power off and restart, since the heat would not dissipate that quickly.

    I note that certain functions like keyboard reset work no problem right off the bat.

    I guess I'll check out the caps now (though I'm not great at that) and replace em.. see if that helps.

  3. #13

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    Do you have a scope or logic analyzer you can use to check if the keyboard provides data immediately from power up? With even just a logic probe you can verify the keyboard's behavior as far as its data strobing and special signals at J3. Now, what the data it strobes actually is might require more than just a logic probe or scope - maybe a separate test jig that can power the keyboard and latch it's data for checking?

  4. #14
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    I'm still mastering my scope but as far as I can tell, yes, data is being generated on power up. Take that with a grain of salt though. I've also checked for pulses as keys are being pressed, things seem to line up with the Theory of Operation, anyway.

  5. #15

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    If you're getting a good data-ready indication from the keyboard at power-up and nothing's being displayed at the monitor prompt I'd think the problem is on the mainboard. Obligatory question: are the power rails good from a power-up (and do they stay good)?

  6. #16

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    First confirm that this problem does not happen with a different monitor, it might not even be your SOL that is the problem. Next I agree test the caps related to your keyboard circuit using an ESR meter. I would not shot gun replace them though, you can disconnect from their circuit by removing one of the posts' connection and then test with an ESR meter. This is a point of discussion that comes up from time to time, replace ALL the caps or just find the ones that are known-bad. I guess it's up to you and your solder skills.

    This one will work:
    https://www.ebay.com/itm/Anatek-Blue...y/263722628688

    There are cheaper ESR meters, but you don't want to go too cheap.

    b
    @ BillDeg:
    Web: vintagecomputer.net
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  7. #17
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    I may have found my problem while trying to solve another. I have the Sol connected to a power bar and use the switch on that to shut it down or turn it on as the switch on my Sol is getting unreliable. Anyway, I accidentally sort of half pressed it causing it to *very* rapdily cycle power which knocked out the Sol entirely and left me with a screen full of junk.

    Anyway, I know I've got some issues with sockets in my machine so I reseated a bunch of chips and while doing so found the plastic part of the socket at U28 (74163) lifted right off the pins! Anyway, I did my best to reseat that and as I did, I noticed on power up I had both the normal prompt again (whew) AND the keyboard was working immediately! I shut down again, reinstalled the spare memory board... powered up.. nothing from the keyboard. Pressed on the 163 carefully but firmly.. voila.. typing starts again!

    Not sure if it's the 163 or some kind of micro-fracture in the PCB. I don't know for sure but I don't recall U28 being involved with the keyboard. Anyway, pressing there seems to get the keyboard working again and it'll stay working for a long time.

  8. #18

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    U28 isn't in the keyboard path but it is in the display path, so a problem there might make it appear to be a keyboard issue. See drawing X-18: it's the character clock divider.

    It give me the creeps every time the board flexes! I dread the day a trace fractures. At least we have nice, pliable, leaded solder elsewhere!

  9. #19
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    Yeah. I kind of think it might be a trace or something in that same area that does have something to do with the keyboard and it's getting flexed in just the right way as I'm pressing on U28. I should investigate further but I really don't want to take the whole thing apart to get the motherboard out.

  10. #20

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    Maybe use the SOLOS command "SET O=1" to change the default output from the video section to the serial port and use a connected PC to display the output. That should show if there's actually a keyboard-input problem or (just) a video-section problem.

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