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  1. ef1j95

    Did the MITS Altair 4K Board Not Work Back In The Day?

    I have SSM, Vector Graphic, and Duston 8K boards in my IMSAI. Lots of 2102s. Those last two are notable because they show up in Ward Christensen and Randy Suess's article about their first BBS in Byte Vol 3, #11, 1978. They note the additional memory they purchased: "We are now running an 8 K...
  2. ef1j95

    Did the MITS Altair 4K Board Not Work Back In The Day?

    Manes' biography of Gates has some good details about the MITS DRAM boards and MITS economics at the time (chapters 5 and 6). The RAM cards were an important money maker for MITS, and the flakiness of the boards contributed to a lot of resentment among customers (including not paying for BASIC...
  3. ef1j95

    Building a Clone MITS 8800

    Been following along, enjoying the discussion. I'm in the final assembly stages of an Altair 8800c, too. I'm waiting on Q1 (2N4410), which I unfortunately forgot to order. I powered up the unpopulated CPU board (minus Q1) and one thing I'm seeing is that the unloaded 12V on the CPU board is...
  4. ef1j95

    SSM-IO2 as a serial card

    @glitch has boards available through Tindie at $30. The rest of the parts are about $30 or so. The cost of assembly at $500 / hour is approximately $10,000.
  5. ef1j95

    SSM-IO2 as a serial card

    I finally got around to building up a Glitch Works reproduction SSM-IO2 as a serial I/O. It's a straightforward build based on the board manual's schematics. I added an MC1488 and MC1489 to handle the EIA interface as somewhat more period correct parts (similar to the Processor Tech 3P+S). The...
  6. ef1j95

    Altair BASIC VER 2.0?

    I recently had Altair BASIC VER 1.0 loading from paper tape on an IMSAI 8080. The binary came from Mike Douglas' DeRamp.com site. (Details at https://ef1j.org/wiki/index.php?n=Main.Version1). Here's a shot of the cold start routine messages: My question is: Does anyone know if a copy of...
  7. ef1j95

    Polymorphic BP/5 motherboard power

    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 a picture:
  8. ef1j95

    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 supply let out a burst of magic smoke. Can anyone post a picture of their Poly-88 backplane...
  9. ef1j95

    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 1.4. I think I've narrowed it down to an 8K board addressed at C000-DFFF. I'm running a bunch of...
  10. ef1j95

    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 work: # Northstar Micro-Disk System MDS-A1 diskdef ns seclen 256 blocksize 1024 tracks...
  11. ef1j95

    Sol-20 serial settings question

    The behavior of my Sol-20 differs from that documented in the manual - presumably a mistake in the latter. The differences are in the parity bit settings and the total word length setting. The manual states that S4-2 and -3 should be OFF and ON for 7-bit operation. I confirmed that it is the...
  12. ef1j95

    SOL-20 UVEPROM module - help.

    Another 5204 board here. I was worried about the state of the ROMs, too, but didn't have a problem. Keep posting as you restore. I had a few head-scratchers with my Sol.
  13. ef1j95

    Seeking Osborne 1 keyboard latch

    Mine was pretty yellow. My retrobrighting worked fine and without marbling. I am skeptical of retrobrighting in the sun, although others report fine results. I suspect that heating and the resulting poor temperature control, which should affect the reaction kinetics significantly, makes the...
  14. ef1j95

    TDL SMB Repair Writeup

    Photo of the SMB2 board I have:
  15. ef1j95

    North Star Micro Disk System question

    Thanks! This is great info. I had come across those two pages before, but had totally forgotten about them. The setup Glitch has is closest to mine, only I have a single drive enclosure. I see you fabricated a mounting bracket for the power board. Mine is mounted to the drive with about 1.25"...
  16. ef1j95

    North Star Micro Disk System question

    I've been working on a North Star MDS system for my Sol-20. I have the MDC-A1 controller and the rebadged Shugart SA-400 in the "North Star MICRO-DISK Cabinet (MDS-CAB)". My drive was set up with the power regulator option to take unregulated +9V and +18V, usually from the power rails of the...
  17. ef1j95

    Victory! Sol-20 repair

    Almost there...
  18. ef1j95

    Victory! Sol-20 repair

    I had to share a hard-won victory getting this Sol-20 up and running. I'll post repair notes to my site soon. It involved a few iterations of power supply, PC board, and keyboard troubleshooting. Next up is refurbishing the keyboard, a topic of much discussion on the board. I'm planning to...
  19. ef1j95

    Early Sol-20 Restore

    I currently have a Sol keyboard open, too. Much of the foam seems to be holding (barely) but a few pads have fallen apart. I was puzzled to find the adhesive membranes after reading much about the "snap-in" disks. They are more flexible and thinner than double stick tape. It looks like the...
  20. ef1j95

    Seals 32KS RAM board

    I have a Seals 32KS, a 32K static RAM board. Searching for information or ads on this board has not yielded much. The 8KS SRAM board manual is available online, but I've only found scant references in the old journals to the 32KS, mostly in quarter page ads of mail-order retailers. I'm guessing...
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