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Macintosh 512k: Strange Beeps During Boot


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After recapping my Mac512's Analog Board and booting either from a floppy disk (in the internal 400k drive) or booting from the FloppyEMU, with the case back off, I can faintly hear some beeping sounds coming from the area of the analog board, but it doesn't seem to be the speaker that I can tell.  Here's a recording of the entire boot sequence, booting off the FloppyEMU:

 

Mac512k_FloppyEMU_BootSounds.mp3

 

Honestly, I can't remember if I had heard these sounds before the recap, since I normally have the case on.  The flyback is good (and tested in a dark room), but it wouldn't make beep sounds anyway, and certainly not during floppy access.

 

Again, there are no sounds like this at all normally.  The sounds only occur during floppy drive access, whether the 400k drive or the externally connected FloppyEMU.  Voltage is a rock solid 5.0V during the floppy drive access, so that isn't an issue.  I also checked the voltage on a scope, before and after the recap, and there was no change after the recap.

 

I recapped the motherboard (stock 512k, with 64k ROMs) many years ago using tantalum capacitors.

 

I'd appreciate hearing your thoughts.

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