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Thread: Osi c4p

  1. #1
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    Default Osi c4p

    So for Xmas I got myself this C4P system from its original owner. Looks great, lots of manuals, etc. Same guy I got the tapes from.

    20191225_151853.jpg

    The machine is presently locked up - cannot get to the usual prompt yet. It was doing this on startup -- no response on Break.

    initscreen.jpg

    So I decided to check the RAM in the video board first. This is what happened when I swapped it with RAM from the 527 board:

    20191225_202533.jpg

    It responds somewhat to Break now.. sometimes the random characters will change, or columns will blank, etc.

    I'm going to use my Hazeltine to check out all the RAM. One thing I'm not sure about.. the 527 has 4 rows of 8 2114s, *except* for the last two rows... for some reason the first chip for each row was left out. I've got an email to ask if that was intentional.. I'm wondering if the memory has been remapped and maybe my having the 527 out for diagnostic purposes is messing things up.

  2. #2
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    Got it! Bad RAM. I used my Hazeltine 1510 as a RAM checker, with bad RAM showing up as screen garbage. There were 9 bad chips , a few on each of the three boards. Once that was done, and after about 20 minutes of forgetting to put shift lock down, I got it to go into BASIC. I had a feeling this would probably be a quick win.

    20191226_170235.jpg

    Almost - I'm not sure why it's repeating everything over and over again. It looks like it almost has the full number of columns, possibly loss of 2 of them. I was looking at Tezza's video on the C4P and it it looks like the columns extend outwards a little bit further, it possibly should say 3.2 (or 3.something) as the BASIC ID and that is cutoff.

  3. #3

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    Tezza's looks like it's 64 columns, but yours is 32 columns and repeating. I'd suggest to have a look around the chips in the video section.

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    Yeah it should be 64 columns for sure. I'm thinking this is probably a problem with one of the 74163 counters. Thing that sucks is, they're all soldered, so it's not a matter of quickly swapping to see if anything changes.

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    Unngh. So much for a quick project.

    For reasons unbeknownst to me, the previous owner only socketed some ICs, and of course none of the 7 74163 counters I suspect may be responsible for my repeating column predicament. This is very similar to what I ran into with that homebrew TV Typewriter I was working on - in that case one of the 74193 counters was at fault.

    Unfortunately this board has been messed with multiple times, and I've had pads coming off quite easily. So I'm resorting to scarce Soldercon replacements because in some places the pads are lifting traces and it's just easier to solder things to these up top rather than try to thread wire around.

    The downside is each counter has pins 3-6 linked, so where I broke that I'm trying to solder things together without the solder filling up the actual pin socket. Yeah... but on the plus side, I ended up watching a video on how to clean and improve my fancy metal solder sucker, and it is absolutely killing it getting solder out of tricky places.

    20191227_190225.jpg

    Hope I'm on the right track here.

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    Darn. I checked everything thrice but on power up there is no video. I can see a clock on the 163s but there is no clock or activity on the 2114s. I'm guessing something like a trace broke somewhere during the 74163 removals. I'm following the schematics backwards to see if I can isolate the problem.

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    Well, I've battled it to a slightly better place. I've now found the bad 163 that was causing the repeating column issue, and I can now get a proper prompt when I hit Break. Unfortunately, now it will not accept any of the C/W/M commands. If I hit almost any other key the prompt 'winks' and comes back, as though I've hit a wrong key, but if I hit C, W, or M.. nothing, no reaction at all. Not sure what the issue is - this isn't the usual parallel ASCII keyboard I'm used to.

  8. #8
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    Default

    Quote Originally Posted by falter View Post
    Well, I've battled it to a slightly better place. I've now found the bad 163 that was causing the repeating column issue, and I can now get a proper prompt when I hit Break. Unfortunately, now it will not accept any of the C/W/M commands. If I hit almost any other key the prompt 'winks' and comes back, as though I've hit a wrong key, but if I hit C, W, or M.. nothing, no reaction at all. Not sure what the issue is - this isn't the usual parallel ASCII keyboard I'm used to.
    Do you have the caps lock on ?

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    Quote Originally Posted by gekaufman View Post
    Do you have the caps lock on ?
    Yeah, I've gotten tricked by that a few times. This is something different. It's like whole rows of the key matrix are out. Some work, but some don't. Everything on the row with the C key is dead, same with W and M... kind of coincidental since you need one of those keys to do anything.

    I don't see anything changing at the keyboard cable header with the affected keys... but it does change with the others.

  10. #10
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    Defintely doesn't seem to be the keyboard at fault, based on my testing. I swapped another OSI keyboard in and the behavior is the same. I'm guessing we're still having problems on the video board, which will require another thorough going over. I'm getting to the point where I may just give up on this board, which has been hacked all to h--l by the previous owner, and build the bare original board I have here.

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