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« Last post by lookes on Yesterday at 07:29:21 PM »
OK. This board is done. The corrosion was not serious. Cleaned up nice.
The audio noise was 'terrifying' lol with the MML2 board. As expected for a 500, or 501 board. This board is a 500 REV D.
I made sound level tests on this board with and without the new rework I have, as well as a random 504B board.
The background noise level in my shop is about 31 dBA. I measured the levels at 3 inches from the right speaker.
'Before' is without any modification. 'After' is with the rework. 'Random 504B' is just a handy 504B board for reference.
Remember that a 10dBA difference is double the apparent audio volume, or half the volume depending on which way it goes.
While booting:
Before - 62dBA After - 49dBA Random 504B - 42dBA
Reel Spin Noise:
Before - 81dBA! After - 60dBA Random 504B - 60dBA
Booted and at Idle:
Before - 62dBA After - 47dBA Random 504B - 53dBA
Tested with sound volume set at zero. The volume of the background noise is unchanged and unaffected by the volume number in settings. The noise level is the same with the volume set at 0, or at 10. The noise enters through the power rails on the digital potentiometer chip on the MPU. Noise is introduced via the 5v supply voltage, and ground level fluctuations. Also some of the noise is inductively coupled from nearby traces. Most of the static you hear (not reel spin noise from the stepper drivers) is related to SENET signal activity.