> On Nov 7, 2022, at 8:27 PM, Robert Armstrong <[email protected]> wrote:
>
>> Paul Koning <[email protected]> wrote:
>> 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
> it's running.
>
> 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
> rotating.
>
>> 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.
paul
