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Microbee Main boards

Standard Main boards

  • There are many variations of the Standard Main board.
  • All variants provide standard graphics only.
  • The board could be modified to use the optional add-on colour board. Viatel video and de-glitching boards were also other optional add on boards.
  • The board number is marked on the solder side in the keyboard section.
  • Some versions have 'MICROBEE Z80 S.B.C' marked on the component side as part of the silkscreen.

 

Board Number Board Colour S.B.C Mark Component Side Image Solder Side Image
  • Notes
P/N 1248 REV 1
P/N 1248 REV 1A
P/N 1248 REV E Blue No MB 1248 Rev E Top MB 1248 Rev E Bottom
  • Used for the Microbee Kit.
  • Corresponds with kit Construction Manual "MicroWorld Publication MWP 28/82 (last revision 29/3/81)". Note that the revision year of 81 appears to be an error - should be 82.
  • Uses a single TO3 type voltage regulator that mounts under the board and is attached to the metal base plate of the case for heat sinking.
  • Video circuit resistor R25 is not present.
  • Has a White Space Bar and RESET key labelled as REPT.
P/N 1248 REV F Blue or Green No PN 1248 REV F   Component Side PN 1248 REV F   Solder Side
  • Used for the Microbee Kit.
  • Corresponds with kit Construction Manual "MicroWorld Publication MWP 28/82 (last revision 6/6/82)"
  • Uses dual TO-220 type voltage regulators with pre-attached heat sinks that are installed under the keyboard frame similar to later factory built models.
  • Video circuit resistor R25 is present.
  • Has a Gray Space Bar and RESET key labelled as RESET.
P/N 1248 REV G
P/N 1248 REV H Green Yes P/N 1248 REV H - Front P/N 1248 REV H - Back
  • There are 2 modifications to this board. 1/ Upgrade from 2mHz to 3.375mHz and 2/ Allow it to be used with a DRAM disk coreboard.
1248-1-06
1248-3-02W Green Yes 1248-3-02w_top 1248-3-02w_bottom
1248-4-02W Green Yes 1248 4 02W   Component Side 1248 4 02W   Solder Side
  • Used for the CIAB.
  • The board in these images has been modified to provide a CGA video output in addition to the standard composite video.
1248-6-02W Green Yes 1248-6-02w_top 1248-6-02w_bottom
  • Has holes for extra keys.

 

Premium Main boards

  • The Premium and Teleterm models use the Alpha+ graphics enhancement.
  • An optional SN76489AN sound chip location was provided but not used on production models.
  • The Teleterm model had an add on keyboard interface circuit so that it could be used with the more modern TC keyboard.  This was connected into the optional sound chip (SN76489AN) position using an IC header plug.
  • Later Premium models had the option to fit a battery backed RTC to the main board.
  • Variations exist in how the inverse/flashing attribute works between different version of the main board along with the RTC and other areas of the design.
  • Board numbers are etched on the solder side at the bottom edge of the keyboard section and are also screen printed on the component side near the DIN connector. Different numbers may exist on each side.

 

Board Number Solder Side Board Number Component Side Colour Component Side Image Solder Side Image
  • Notes
8501-3-02W
DRG8501-3-01
8501-3-04CR Green 8501_3_04cr_top 8501_3_04cr_bottom
  • Board number location (front or back) to be confirmed.

8501-4-02W
DRG8501-4-01
8501-4-04CR Green 8501 4 04CR   Component Side 8501 4 04CR   Solder Side
  • Used for TeleTerm and Premium Plus+.
  • The board in these images includes Premium Plus+ modifications.

 

256TC Main boards

  • The 256TC model uses the Alpha+ graphics enhancement and adds a new type of keyboard.
  • Unlike the Standard and Premium Main boards, there is no additional plug-in Core board for the 256TC. All components are installed on the Main board with the keyboard being a separate unit.

 

Board Number Colour Component Side Image Solder Side Image
  • Notes
MB 8508-2 Dark Green 256TC Top 256TC Bottom
  • This picture is of a repaired board following a battery leak.
  • On the component side, some silkscreen markings are missing on the left side and replacement components have been fitted.
  • The solder side image was taken prior to fitting the replacement components.