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**SPX-MPU schematics**

SPX-MPU is a 6-layer pc board with power/ground layers in the middle. On some pc boards it is easy to see the inner layers clearly. This is how schematics are derived:

Remove all components.

Take high resolution photos of the bare board, component side and solder side.

Overlay the component layer with the solder layer in Photoshop

Manually trace the signals, switching layer in Photoshop as the trace switches side. Use continuity meter to verify connections where needed.

There are two sheets of C size schematics and one size B schematic. Please note these are schematics of the original pc board. They do not reflect subsequent engineering changes.

[[https://www.retrobrewcomputers.org/lib/exe/fetch.php?media=builderpages:plasmo:spx-mpu:adc_mpu_scm.pdf|CPU/memory]] schematic (updated 11/25/17),

[[https://www.retrobrewcomputers.org/lib/exe/fetch.php?media=builderpages:plasmo:spx-mpu:adc_io_scm.pdf|I/O schematic]] (updated 11/25/17).

[[https://www.retrobrewcomputers.org/lib/exe/fetch.php?media=builderpages:plasmo:spx-mpu:adc_reset_scm.pdf|Reset logic schematic]] (updated 11/25/17).