FOR SALE -- Southwest Technical Products Corp. 6800/6809 Computer

I bought my Southwest Technical Products (SwTPc) MP-68 6800 Computer System as a kit over 43 years ago in its minimal configuration. Over the next few years I expanded the memory, added a floppy disk drive system, upgraded to the 6809, and made various other changes. This was my main computer system for about 6 years, but I continued to use it occasionally for several more years.

On October 25, 2021 I successfully booted the FLEX and STAR-DOS operating systems on it again, for the first time in over 23 years! (See screen shot below.)

For Sale

Now it's your turn to own this piece of microcomputer history.

Did you own a SwTPc 6800 or 6809 system in the past, got rid of it years ago, but now wish you had kept it? Or you never owned one, but would have liked to? Here's your chance to own a vintage system in working condition -- don't wait until after it's gone.

I am the original owner of all items listed on this page, except for the MP-N and SC1-B.

Note that additional information about some of these items is available on my web site.

On October 31, 2021 I placed an ad for this system on Craigslist. I'm hoping to sell it locally for pickup so I don't have to spend the time and effort and expense to carefully package it for safe shipment.


(Click on a picture for a larger version.)
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It boots!! (68KB .png)
Pictures of my SwTPc 6809 system. (465-771KB .jpg)

Tested (and currently working -- if you pick up the system at my place I can demonstrate it running)

Note that due to the age of this system, there is no guarantee as to how well these items work or how long they will continue to work -- they are sold as-is, no returns or refunds.

The eight items on this list will be sold together as one package: 

  1. SwTPc MP-F chassis:
    - four cutouts for DB-25 connectors on rear panel
    - 7 extra holes drilled in base to better mount motherboard
    - does not include perforated cover or trim pieces to cover edges of perforated cover
  2. SwTPc MP-P power supply:
    - separate +/-12.6VAC 2 amp transformer added for +/-16VDC supplies, mounted on rear panel
    - two 1000µF 25V capacitors replaced with three 2200µF 35V capacitors
    - four 1N4003 diodes replaced with 1N5403 (3 amps)
    - all four large capacitors (one 91000µF 15V, three 2200µF 35V) recently reformed
    - original nylon board supports replaced by four standoffs with machine screws/washers/nuts
    - original printed manual: Assembly Instructions (with my modification notes)
  3. SwTPc MP-B motherboard:
    - 7 extra holes drilled in it for more secure mounting to reduce flexing of board when cards are inserted or removed
    - 14 standoffs with machine screws/washers/nuts used to securely mount motherboard onto chassis base
    - all 5 baud rate lines disconnected between SS-50 and SS-30 bus to support 20-bit address bus
    - wires to /M.RST, UD1, UD2 bus lines removed
    - I/O physically located at $8000-$9FFF (but logically accessed at $E000)
    - I haven't yet determined all modifications made to the motherboard for 6809 and 20-bit address bus -- will update this page as I find it
  4. SwTPc MP-09A 6809 CPU board for SS-50 bus:
    - 1 MHz MC6809
    - MC14411 baud rate generator not installed
    - R21, R22, R23, R24 and second 74S189 installed to support 20-bit address bus
    - SBUG-E 1.5 monitor in EPROM, modified for I/O physically located at $8000 but logically accessed at $E000
    - original printed manuals: Assembly Instructions for MP-09, SBUG-E 1.5 User's Guide
    - 220µF 10V electrolytic capacitor replaced with new 25V device 2021-Oct
  5. Micom DR8264-68 64KB DRAM memory board for SS-50 bus:
    - 8 64Kx1 single-supply DRAM chips
    - $0000-$7FFF and $A000-$DFFF enabled, $8000-$9FFF and $E000-$FFFF currently disabled
    - supports 20-bit address bus, but currently disabled
    - user manual with schematics available on my web site
    - 220µF electrolytic capacitor replaced with new 25V device 2021-Oct
  6. homebrew dual serial port card for SS-30 bus:
    - built with wire-wrapping on a Percom prototyping board
    - two MC6850 ACIA ICs
    - 1488 and 1489 RS-232 line driver and line receiver ICs
    - MC14411 baud rate generator with 1.8432 MHz crystal, also feeds 5 baud rate clock signals to SS-30 bus
    - three voltage regulators for +5V, +12V, -12V
    - 12-pin Molex I/O connector, 6 pins per port: GND, TxData, RxData, /RTS, /CTS, /DCD
    - currently has /RTS connected to /CTS and /DCD using wire-wrap wire, for both ports, can easily be removed
    - new wiring for first port connects only GND, TxData, RxData to DE-9S connector, but with /RTS shorted to /CTS and /DTR shorted to /DSR at DE-9S end, for easy connection to PC with straight-thru cable
    - second port not currently connected or tested, but an older wiring harness that brings all 12 pins to two DB-25S connectors is also included and can be installed instead for use with vintage equipment
    - can't find any schematics for it
  7. SwTPc DC-2 floppy disk controller board for SS-30 bus:
    - supports single-density (FM), single-sided
    - added a Percom SEPARATOR floppy disk data separator daughterboard for improved reliability
    - replaced two zener diodes with 7812 and 7905 voltage regulator ICs
    - ribbon cable and floppy disk drives not included
  8. floppy disks:
    - bootable 5¼" 35T/SS/SD disk with FLEX 9.0, including TSC editor and assembler and single-drive copy program
    - bootable 5¼" 35T/SS/SD disk with STAR-DOS LEVEL I (1985-Jun-15 version)


Untested (might work, or not)

These items are not guaranteed to work -- they are sold as-is, no returns or refunds.

If the purchaser of the "tested" package doesn't take all six items on this list, then the remaining items will be offered for sale individually:

  1. SwTPc MP-A2 6800 CPU board for SS-50 bus: 
    - 1 MHz 6800
    - MC6810 128x8 SRAM
    - SWTBUG 1.0 monitor in ROM
    - original printed manuals: System Checkout Instructions, SWTBUG 1.0 Users Guide
    - was working when last used approx. 40 years ago
  2. SwTPc MP-LA parallel port board for SS-30 bus 
  3. SwTPc MP-N calculator board for SS-30 bus: 
    - original printed manuals: Assembly Instructions, MM57109 data sheet
    - was obtained used, but I never installed or tried it
  4. UNITEK EPRAM EPROM programmer board for SS-30 bus: 
    - 28-pin and 16-pin ZIF sockets
    - programs 2508, 2758, 2516, 2716, 2532, 2732, 2732A, 2564, 2764, 2528, 27128
    - personality module for 2732A included -- user manual provided information on making new ones
    - two LEDs indicate when low voltage and high voltage supplies are on
    - gold-plated SS-30 bus connector
    - was purchased assembled and tested, not built from a kit
    - I probably have the user manual for it, but have not found it yet -- will post a scanned copy on my website when I find it
    - the QED2716.CMD program on the included bootable FLEX disk appears to be a version of the software for programming a 2716, but have not yet found the original version
    - was working when last used approx. 30 years ago
  5. Microware SC1-B serial port board for SS-30 bus: 
    - only partially assembled
    - can't find any documentation for it
  6. Percom prototyping board for SS-50 bus: 
    - bare PCB, never used, ready for your custom project





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Last revised 2021-Nov-04 11:05 PDT.
Copyright 2021 by David C. Wiens.