OSI-300 Mini Assembly

Assembly of the OSI-300 Mini is fairly straightforward.  I typically start with the shortest height parts, and work up to the tallest.

  1. 1N4148/1N914 diodes D1-D20, D41, D42, and D43
    The black bar on each diode matches the bar on the silkscreen.
  2. 220 ohm resistors R1-R32, R35, and R39
  3. Remaining resistors:
    1. 4.7K ohm resistor R33
    2. 100K ohm resistor R34
    3. 100 ohm resistor R36
    4. 2.2K ohm resistor R37
    5. 4.7K ohm resistor R38
  4. 1N4001 diode D44
  5. .1uF capacitors C1-C5, C7-C9 (Lead spacing: 2.54mm/.1in)
  6. 10pF capacitor C6 (Lead spacing: 5.08mm/.2in)
  7. Sockets (five 14-pin, one 40-pin, one 28-pin)
  8. 3mm LEDs
    The flat edge matches the flat edge on the silkscreen.
  9. Switches
    There are two single-pole double-throw switches wich are different. They are to be used for the run and reset switches. They can be identified by the two slots on the side of the switch body.
  10. Single pin headers
    These should be broken out of the 6-pin breakable header
  11. Jumper
    I usually take a cut lead and bend it into a jumper to bridge the two pads above R34
  12. IC installation
    1. 7417N U1-U4 (buffers)
    2. 6502 U5 (CPU)
    3. 6264 U6 (SRAM)
    4. 7402 U7 (output)
  13. Rubber Feet
    I included two rubber feet to be placed under the OSI-300 Mini. They are too big to fit as-is, but can be cut with a sharp pair of scissors to form four half-circles.

A schematic of the PCB board can be found atminitrainer.pdf

I have found that I can test the board without the CPU and SRAM to ensure that the switches work properly by turning off/on the LEDs with the RUN switch set left.

The operation of the board can be accomplished by following the manual at Dave’s OSI repository

I’ve found that while programming, it is necessary to ensure that the RUN is left and RST is right. To run the program, switch RST left, then right, then switch RUN right, followed by RST to the left.  This sequence ensures that the clock starts properly.

Paul has also pointed out that the reset address used in the OSI manual needs to be adjusted due to the extra address lines.  In place of 7C and 7D, you will want to use FFC and FFD.

Update: at this point due to issues with the postal system I no longer will be mailing kits.  If this changes, I will update this post.

16 thoughts on “OSI-300 Mini Assembly”

  1. Hi, I would like to purchase an OSI-300 kit. You were selling them at VCFMW, however I’m over in New England so I couldn’t attend. Is it possible for me to order one, or do I have to attend one of these gatherings?

  2. This project is interesting. Will you sell this as a kit for people like me without too much electronic background to build it ?

    1. Re OSI-300 replica.. is there a kit or pcb’s for this? .. interested in getting one .. as I was about to do pretty much the same ..but all this has been done ..so no need to reinvent it …

  3. I finally got around to putting the kit you sent me together last night. Let me start off by saying how impressed I was with the organization of parts, quality of the instructions, etc. It was a real joy to put together, and it seems to be working just fine. Now I just need to spend the time learning how to drive it. 🙂

    I did find one minor correction for your assembly instructions as posted on the web page. Step #6 says 10nf capacitor in C8. I started with that one…fought to make the leads fit (thought it odd it had to be bent to make it fit the smaller lead spacing in the board for C8), then put the .1uf’s in and had an extra…then realized the 10nf should have gone in the C6 spot, not C8 as indicated. 🙂 Guess I should have checked the rest of it over more carefully first! Oh well…

    Thanks again for all the hard work you put into this, it will be fun learning and using.

    1. Wesley,
      Thank you for the kind words, and correction to the instructions. I have updated the page to reflect the correct notation.

      I still have additional assembled systems, full kits and board+switch kits available to individuals interested in them.

      1. I would love to get one of the kits, if there are still some left. Would you get in touch with me regarding the ordering process?

  4. This kit seems amazing to show some early computing techniques. Do you have some kits left? I would like to purchase one if possible.

Comments are closed.