8 Nov
2022
8 Nov
'22
6:58 a.m.
-----Original Message-----
From: Paul Koning via cctalk <cctalk(a)classiccmp.org>
Sent: 08 November 2022 01:34
To: Bob Armstrong <bob(a)jfcl.com>
Cc: cctalk(a)classiccmp.org; Paul Koning <paulkoning(a)comcast.net>
Subject: [cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2
drives ...
On Nov 7, 2022, at 8:27 PM, Robert Armstrong
<bob(a)jfcl.com> wrote:
Indeed, but I was reacting to the statement that the DEC part is strange Paul Koning <paulkoning(a)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. 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