On Nov 7, 2022, at 8:27 PM, Robert Armstrong
Paul Koning <paulkoning(a)comcast.net>
Does the tachometer have to be accurate, or does it just have to indicate
"spinning fast enough" to satisfy the spin-up logic?
It's not just spin up - the firmware monitors the disk speed all the time
But AFAIK the tachometer has nothing to do with how the bits are recorded
on the media. It's just there to be sure the disk is actually
If not, you could just use a 555 to generate a
pulse train ...
Maybe, probably, but I'm not sure why you'd want to. That's way more
complicated than just fixing the tachometer sensor, and having the firmware
shut down the motor in the event the belt breaks or jams, or if the motor
brake (yes, it has a brake!) freezes, etc is an advantage. It's a fairly
big motor and a fairly (by PC standards at least) heavy disk - there's a lot
of mechanical energy there.
Indeed, but I was reacting to the statement that the DEC part is strange and hard to find.
So if that turns out to be barrier, faking the tach signal would be a way to make the
drive operational again.
Another approach would be a bit of mechanical work to fit a stock optical sensor. That
would depend on having access to the needed machining skills.