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    Dwight was right. Despite the DO-35 glass cases,...

    Dwight was right. Despite the DO-35 glass cases, the diodes were 1N4003, just as the Poly-88 parts list states. (I haven't been able to find glass replacements... only the DO-41 plastic.) I think D3...
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    Super! Thanks for the leads. I'll try to get it...

    Super! Thanks for the leads. I'll try to get it apart this weekend to take a closer look. In the meantime, I happen to have 1N4001's on hand, so if those died it will be an easy repair.
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    Do 1N4001-1N4007 come in a DO-41 package? The...

    Do 1N4001-1N4007 come in a DO-41 package? The diodes on my board are DO-35 style. They look like signal diodes. Which is why I was curious what is actually installed on other folk's boards.

    Here's...
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    Polymorphic BP/5 motherboard power

    I'm currently working on a Polymorphic BP/5 motherboard as part of some bowenfusenwerk caused by a shorted tantalum on a card I was testing. After powering the machine back up, something in the power...
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    "I have such a IMSAI setup. In fact I have no...

    "I have such a IMSAI setup. In fact I have no system ROM, on reset it DMAs the first sector into memory. After reset, I just start at RAM address 0 and it loads CP/M with my 100% RAM address."

    I...
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    I definitely benefited from the ideas here. I had...

    I definitely benefited from the ideas here. I had never thought about the lack of indirect addressing for 8080 I/O, nor did I realize that the Z80 had this feature.

    Still curious what the serial...
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    It sounds like you're trying to figure out a...

    It sounds like you're trying to figure out a single machine. What hardware is serving the serial output? Or is this a general problem for a monitor you are writing (as I think Chuck and Dwight are...
  8. Thread: Paper Tape

    by ef1j91
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    988

    I bought a box of 1" tape off an ebay seller....

    I bought a box of 1" tape off an ebay seller. There are a few persistent sellers and you can possibly negotiate a lower price than they list. The seller I used delivered a fine product. My only...
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    Favorite memory check routines

    Nothing says "S-100" quite like memory problems, which seem to crop up unexpectedly and lead to mysterious faults and crashes. My latest escapade has involved DDT suddenly not running on a 63K CP/M...
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    Now that makes sense! I wondered about that 10A...

    Now that makes sense! I wondered about that 10A value.
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    I believe that's the PSU configuration from early...

    I believe that's the PSU configuration from early machines. The large circuit board came later. My machine is S/N > 17,000, one of the last, and it has the PS-28 supply.

    From IMSAI.net / Todd...
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    Back to the point of the original post: Agree...

    Back to the point of the original post:

    Agree with Glitch and Sellam that the asking price for a loaded IMSAI including disk subsystem with single owner, documented provenance is pretty much in...
  13. May I ask what exactly your goal is with the...

    May I ask what exactly your goal is with the IMSAI? You have a nice collection of early microcomputers, but the earliest like the IMSAI are far more fickle. You're going to have to get your hands in...
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    Gorgeous system. Would love to see a museum...

    Gorgeous system. Would love to see a museum curate a good collection / display of home-brew micros. (Do any?)
  15. Replies
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    About 90s in the original 1977 CP/M MBASIC ...

    About 90s in the original 1977 CP/M MBASIC

    https://twitter.com/ef1j95/status/1106955907156586496?s=21
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    OK, toggled in this updated counter program: ...

    OK, toggled in this updated counter program:

    1000:
    16 FF 7A D3 FF 01 05 00
    0B 78 B1 C2 08 10 15 C3
    02 10

    The pause is short and could be accommodated in a single register. It seems that the...
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    That would explain the unexpected behavior!

    That would explain the unexpected behavior!
  18. Replies
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    Cool! I tried entering the simple counting...

    Cool! I tried entering the simple counting program:

    0000:
    16 FF 7A D3 FF 01 FF FF
    0B 78 B1 C2 08 00 15 C3
    02 00

    But when I get to address 000E, entering C3 and "O" sets the PC=C3. Same for...
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    Very clean machine. Cosmetically looks to be in...

    Very clean machine. Cosmetically looks to be in great shape. Probably doesn't come with mud wasp nests, like mine did. The MPU card may be early, judging from the size of the crystal and white...
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    I've had intermittent keyboard issues as well....

    I've had intermittent keyboard issues as well. Usually LOCAL, UPPER CASE, ALPHA LOCK become unresponsive. Other keys that have issues are W, Q, :, and sometimes E. They will work for a while, then...
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    The Sol manual lists the MCM6575 as an alternate...

    The Sol manual lists the MCM6575 as an alternate ROM. Did any actually ship with that character generator?
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    Well, dagnabbit. My brown case OCC-1 worked a...

    Well, dagnabbit. My brown case OCC-1 worked a year ago, but it's showing similar keyboard issues now. Unresponsive keyboard, won't boot. The screen isn't necessarily flickering all the time, but did...
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    Thanks for the heads-up on the MCM66740 (and the...

    Thanks for the heads-up on the MCM66740 (and the MCM6574)!
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    Yes, the disk controller uses 10 sector, hard...

    Yes, the disk controller uses 10 sector, hard sector disks. I have it running with Mike's VSG.

    Not sure why the DSK image would depend on hard versus soft sector, though?

    Interestingly, one...
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    cpmtools diskdefs for North Star MDC?

    Anyone know the correct cpmtools diskdef parameters for single density North Star MDC-A1? I'm using the Lifeboat CP/M images from deramp.com on a Sol-20.

    I guessed this one, but it doesn't quite...
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