> -----Original Message----- > From: Paul Koning via cctalk <cctalk@classiccmp.org> > Sent: 08 November 2022 01:34 > To: Bob Armstrong <b...@jfcl.com> > Cc: cctalk@classiccmp.org; Paul Koning <paulkon...@comcast.net> > Subject: [cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ... > > > > > On Nov 7, 2022, at 8:27 PM, Robert Armstrong <b...@jfcl.com> wrote: > > > >> Paul Koning <paulkon...@comcast.net> 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.
The replacement board does not use the DEC part. > > 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. That is what this mod does > > paul dave
