Image Map Image Map
Page 2 of 2 FirstFirst 12
Results 11 to 20 of 20

Thread: C2-4p

  1. #11
    Join Date
    Dec 2011
    Location
    Dallas, TX
    Posts
    173

    Default

    Nice!! An old-school very early C2-4P with a 500 board. There are not many of those floating around.

  2. #12
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Thanks muchly!

    Does anyone out there have a fix on production numbers for OSI gear? I'm curious how many of these things are out there. They seem to be particularly rare even on ebay.

    I still cling to the hope of collecting a C2-8P. Love that huge case.

  3. #13
    Join Date
    Jul 2014
    Location
    New Hampshire, USA
    Posts
    160

    Default

    The two power supplies are indeed different, the one with the 2 caps is a 5v supply, the other is a -9v supply.

    The caps were likely removed as they are always bad in my experience. I'd bench repair the two supplies before you even think of powering up the system. The 1702A's won't be very happy without the -9v supply. Personally I'd recap both supplies before anything else. They are a very straight-forward 723 regulator based design and pretty easy to repair and adjust.

    I can duplicate the 1702A's if they are defective.

    Also somewhat obviously the 6820 needs to be re-seated.

  4. #14
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Quote Originally Posted by gekaufman View Post
    The two power supplies are indeed different, the one with the 2 caps is a 5v supply, the other is a -9v supply.

    The caps were likely removed as they are always bad in my experience. I'd bench repair the two supplies before you even think of powering up the system. The 1702A's won't be very happy without the -9v supply. Personally I'd recap both supplies before anything else. They are a very straight-forward 723 regulator based design and pretty easy to repair and adjust.

    I can duplicate the 1702A's if they are defective.

    Also somewhat obviously the 6820 needs to be re-seated.
    I think these broke off either in transit or at some point before then. They were loose in the case when I opened it. I'll hunt around here for replacements before I do anything. The 6820 was loose also with the pins all bent in. Still inspecting for critter damage.

    The only thing that makes me nervous with this unit is the AC receptacle on the back. I know it's irrational but something about a homebrew AC adapter strapped into a metal case... heh

  5. #15
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Fixed up the power supply with some spare caps I had around, and after the cursory testing (and hiding under the table in case something blew up), I confirmed voltages were ok. Then I plugged in the cards.. at first, nothing.. but then discovered by wiggling the RCA plug on the back I got video. I got the usual junk screen, hit break, and although the video is a bit messed up I can see bits of the familiar C/W/M prompt in there. So I think she's alive! I really hate that the video card is on the bottom and that everything is wired so tightly that taking it apart involves substantial risk, but it should be a matter of swapping RAMs and away we go.

    I don't know why I'm having so many trust issues with this metal case. I keep imagining it shocking me because of improper wiring. But I've been over and over it and cannot find any broken/frayed/chewed/installed wrong wires.

    I'm glad the fan works nicely. In my C1P it makes horrible rumbling noises... think the bearings are shot.

    Anyway, I'm going to try and fix the video ram problem and then do some testing.

  6. #16
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Hmm. Don't quite know what I'm dealing with here.

    I thought these bands I was getting were due to bad memory:

    20181221_195639.jpg

    The machine was not responding to keystrokes of any kind. While looking things over, I noticed (doh) the keyboard connector was off. So I reconnected it, and now the keys worked. But when I'd hit, say, C, instead of getting the usual prompts for terminal width, etc... I'd just get a ? and anything I typed produced a ?SN error.

    I then realized I hadn't put the 6821 back in. I bent the pins back straight and plugged in. Now when I hit M I went to monitor! When I hit C, I get these prompts:

    20181221_204136.jpg

    You can hit enter at both. I think they are garbled versions of the usual Term Width and Memory Size prompts. But once past those.. you cannot really do anything.

    Not sure what would be the culprit here. I don't think this is a video RAM issue anymore... clearly it's capable of displaying the prompt above in perfect clarity. So I'm wondering about main RAM or something with the ROMs?

  7. #17
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Dang. It appears to be BASIC ROM #3.

    Luckily I had my spare 500 board. I swapped all the ROMs over and right away BASIC started working properly. Then I went one by one and definitely we seem to have a problem with #3. When the 'bad' #3 is installed, BASIC either crashes to that ? prompt, or gives me the garbage in the picture above. With the #3 from my other 500 board.. no problem.

    That kinda sucks.. finding a replacement is likely impossible. I've never seen a spare OSI ROM come up, like.. ever.

    But at least for now i can get this C2 up and running.

  8. #18
    Join Date
    Jan 2011
    Location
    Vancouver, BC
    Posts
    4,171
    Blog Entries
    2

    Default

    Quote Originally Posted by dfnr2 View Post
    The 400 card could only use an ASCII keyboard, not the later polled keyboards. The 542B was available much later, when the 540B cards with color came out.



    All C2-4P and C2-8P systems had 32x64 displays with the graphics characters. They used the 540(aka, 540A) video boards, which were B&W only. They were shipped with the polled keyboard (542) but could also interface to an ASCII keyboard.

    The early C2-4P versions came with the 500 board. Most came with the 502 board or 505 board, depending on whether they were factory configured as cassette or floppy systems.
    I've a question - for a test, I entered the program I did with my C1P in this video: https://www.youtube.com/watch?v=25QUpOHNNNY

    And it did not produce any graphics.. no starship like in my video above.. just letters. Are the graphics character mappings different for the 500 boards? Or do they exist at all?

  9. #19
    Join Date
    Dec 2011
    Location
    Dallas, TX
    Posts
    173

    Default

    ROM#3 is the where the garbage collector bug lives. It is (and was) common to replace it with a 2716 containing a patch for the bug.

  10. #20
    Join Date
    Dec 2011
    Location
    Dallas, TX
    Posts
    173

    Default

    Quote Originally Posted by falter View Post
    I've a question - for a test, I entered the program I did with my C1P in this video: https://www.youtube.com/watch?v=25QUpOHNNNY

    And it did not produce any graphics.. no starship like in my video above.. just letters. Are the graphics character mappings different for the 500 boards? Or do they exist at all?
    I noted that your earlier post described an ?SN error. There was a bug in the OSI version of Microsoft BASIC that resulted in a graphics character being printed instead of the second character of an error code. This was because the highest bit was used to indicate the end of the error code. The OSI version of BASIC had a bug and didn't strip off that high bit, resulting in a graphics character instead of the letter. For example, N is $4E, but with the high bit it's $CE, which looks like a little elbow pointing up.

    That means the high bit is not affecting the character. Here are a couple of possible explanations:

    1) You have a 2513 character generator instead of the OSI ROM Graphics character generator.

    2) You have the graphics character generator, but your high-bit 2102 chips are missing; or there's a bad multiplexer bit, or a bad 8T26, etc., affecting the high bit (in order of more -> less likely.)

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •