XO1.5 1.2V power sequencing ECO

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Scope

This describes a change to early prototypes of the XO-1.5 motherboard. It fixes a problem with the sequencing of power supply turn-on to the VX855 chip.

This only applies to XO-1.5 A-phase (both A1 and A2) motherboards.

Procedure

  1. Remove R234. Use one pad to provide PRE_MAIN_ON.
  2. Lift PU7, pin 6 (near PL6) and tie it to PRE_MAIN_ON.
  3. Tie the MAIN_ON (U3, pin 1) signal to +1.2V_GD (D12, cathode).
  4. Remove PR67 (This is a quick fix. Ideally, pin 2 of PQ20 should be lifted and tied to an inverted, high voltage version of PRE_MAIN_ON).

Results

This page is still a scratchpad testing a hypothesis.

Done to:

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