10 Jan
2010
10 Jan
'10
5:20 p.m.
Tony Duell wrote:
Side 1 head. Upper head. Side 0/lower reads OK, side 1/upper reads as
garbage.
As an aside, this is a major problem on the
full-height Sony 3.5" drives.
They were originally lubricated with a grease that turns hard and sticky
with age. The result is that the eject mechansim doesn't lock in the 'up'
posiiton properly. When you try to eject a disk, the upper head will
catch in the slot of the disk itself and will be ripped off the gimbal
spring. This drive was used in a lot of HP devices, if anyone has ole HP
3.5" stuff and hasn't cleaned off the grease, do so _now_ before you
haveto ifind a new head assembly and align it!
Sounds similar to what happened with this one -- I had to extract the
disc by opening the drive up and manually forcing the eject mechanism to
work. Unfortunately I pushed the slider too far and knocked the top tray
off the mounting. When I put it back in, I suspect I hit the top head
and either broke it or knocked it out of alignment.
TBH, the
timing histogram from the Sony drive's upper head looks like
Do you mean 'upper head' or 'side 0 head' here? An open-circuit head will produce noise, as will
anything that causes it
not to be connected to the read amplifier.
What's odd is that there seems to be some data there -- one or two
sector headers occasionally decode OK, so maybe the head is just out of
alignment.
That, alas, is nothing like the drive I am thinking
of. Mind you, the
drive I was thinking of is a 720K one (actually the version I know is a
80- cylinder, double hard _600 rpm_ unit, but it came in all sorts of
versions.
That sounds like the drive in my HP 1651B logic analyser...
The drive in the 16500B appears to be a fairly standard laptop-style
(i.e. thin) 300RPM 1.4MB drive, though.
I would still be incined to trace back from the head
connectors. If they
go straight to one of the chips, you may well have big problems, but if
there are any discrete components involved, it's worth checking them.
To be honest I'm not overly concerned about fixing the MPF520. It's a
fairly nice drive in that it has physical jumpers for DS0/DS1 and
density selection (AUTO or PIN-2), but I have Panasonic and Citizen
drives that (at the very least) have the DS0/DS1 switch.
The drive I'm using now (the Z1DE-55A) doesn't have the jumpers, but it
does have a rather fetching black front panel and a green ACTIVE LED...
which I'm very tempted to replace with a blue LED... :)
Without knowing a lot more about the internals of the
drive I can't begin
to guess what is going on :-)
:-)
My best guess is that the LSI contains a flip-flop that's cleared when
STEP transitions H->L, and cleared when it transitions L->H. The FF
output is then used as an enable signal for the RD_DATA and INDEX drivers.
As I've said before: "It works now, or at least seems to."
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/