Image Map Image Map
Results 1 to 2 of 2

Thread: The RICM Just Received a second MITS Altair 8800 Donation

  1. #1
    Join Date
    Jul 2014
    Location
    Rhode Island
    Posts
    1,322

    Default The RICM Just Received a second MITS Altair 8800 Donation

    We recently received a second Altair 8800 donation, Serial Number 223482K. The front panel has one toggle-switch that won't toggle, and won't stop the processor. Altair #1 came with two spare toggle switches so we can fix the front panel in Altair #2. The unregulated 8VDC output in Altair #2 is about 13.9VDC, so we need to fix that. It makes the onboard regulators run really warm! We are not sure what is causing the high voltage. We will connect a 'scope and see if one of the diodes in the bridge is bad. It came with a Tanner Computers 64k Static RAM, Micropolis 1071 Floppy Disk Controller, 88-2 Dual SIO, MITS Revision 1 CPU, and a Micropolis 1023-II diskette. The SIO is configured for RS-232@1200 baud. That will be helpful for testing MS BASIC in the first Altair instead of waiting forever for it to load through the Teletype. Altair #2 came with a Godbout Econoram VII, PSS RAM8, Quantronics MM8, and a MITS 4k Static RAM board. After we fix the Econoram VII we will put the RAM boards in the Altair #1 to replace the misbehaving early design MITS 4K RAM boards.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  2. #2
    Join Date
    Jul 2014
    Location
    Rhode Island
    Posts
    1,322

    Default

    The unregulated +8VDC voltage is really high, but we don't see any way to reduce it other than using a Variac to reduce the line voltage.

    We replaced IC J, an SN7473, in the front panel and now the RUN/STOP works. Since we can now stop the CPU the EXAMINE and DEPOSIT are starting to work. EXAMINE isn't loading the address switches and is actually doing an EXAMINE NEXT, so that will be the next project. The first Altair came with a spare toggle switch and a spare momentary contact switch. We replaced the toggle switch for bit-12 with a new switch, and will try to fix the broken one.

    We replaced the really early design 4k DRAM boards in Altair #1 with the static RAM boards that came with Altair #2. It works much better now. The next project is to program MS BASIC into EPROMs and install them into the Cromemco Bytesaver board.
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

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
  •