19 Aug
1997
19 Aug
'97
2:13 a.m.
<Yes, I'd realised that. I was planning on making a circuit that triggered
<off the index pulse and recorded 'bursts' of (say) 250kHz pulses on the
<disk. A bit of logic would let me record a track offset towards the edge
<of the disk, twiddle the micrometer to move the head to the same offset
<towards the spindle and then record bursts between the ones I'd just put
<down. Now align the target drive so that both types of burst are replayed
<at the same amplitude.
doesn't work, you need the narrower write head. What you will see is
the additive components of the signals where the head overlaps the tracks.
The can be the sum or the signals, if not in sync there will also be
differences due the phases at a given instant. Also do not discount the
effects of the tunnel erase portion of the head slicing off the adjacent
offset tracks.
<The older SA800's used entirely standard logic, so it's not worth taking
<parts from an old one. SA850's used custom chips in the read/write
<circuit, and later SA800's (according to my service manual) used one big
<custom chip :-(. I guess then you have to get spares from old drives.
Sometimes it's easier to swap a known board that troubleshoot.
<Getting _new_ 8" drives is next-to-impossible, and if you use a
True but, there are used and then there are USED. The later being one thats
seen umpty years of 24x7.
<The less said about that SA400 the better....
Yep!
Allison
19 Aug
19 Aug
4:43 a.m.
doesn't work, you need the narrower write head.
What you will see is
the additive components of the signals where the head overlaps the tracks.
Not at all. What I was planning on recording (on a totally blank disk) was
:
==== ==== ====
==== ====
Where the ==== is a burst of data and the centre-line of the desired track
was along the middle of the 2 patterns. The read head output will only
reply the 2 bursts at the same amplitude (assuming they're sufficiently
separated, which will take some experimentation) if the head is following
that centre-line.
The can be the sum or the signals, if not in sync
there will also be
differences due the phases at a given instant. Also do not discount the
There's no way the head will be reading bits of the 2 recorded tracks at
the same time. So cancellation does not apply.
effects of the tunnel erase portion of the head
slicing off the adjacent
offset tracks.
Firstly I'll be gating the WG signal, so I'll not be erasing my
carefully-recorded track, and secondly, I am probably using custom
electronics so I can remove the erase signal altogether if it causes
problems.
<The older SA800's used entirely standard
logic, so it's not worth taking
<parts from an old one. SA850's used custom chips in the read/write
<circuit, and later SA800's (according to my service manual) used one big
<custom chip :-(. I guess then you have to get spares from old drives.
Sometimes it's easier to swap a known board that troubleshoot.
Hmm.... By the time I've found where the fault is (i.e. proved it to be on
a certain board), I'm pretty close to the defective component anyway. The
SA800 is not exactly difficult to trouble-shoot, and I do have the
official service manual.
<Getting _new_ 8" drives is next-to-impossible, and if you use a
True but, there are used and then there are USED. The later being one thats
seen umpty years of 24x7.
I know of only one UK supplier, and they want \pounds 295.00 (!) (nearly
$500.00) per drive. And my experience of this company, based on a friend
buying a 'used but good 5.25" drive' which came with a worn-out spindle
motor, a fault on the speed control board and another on the logic board
means that I'd rather not deal with them. Quite simply, it's cheaper and
less hassle to rebuild what I have.
Allison
-tony
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