10 Jan
2010
10 Jan
'10
4:56 p.m.
Tony Duell wrote:
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!
Firstly, clean the heads -- not with a cleaning
disk (no matter what the
manuals may say), but with a cotton bud and propan-2-ol. I once spent an
afternoon chasing a non-existant fault on the analogue board of a CBM
2850LP that turned out to be drity heads.
I'll strip it again and have another go. But I wouldn't be at all
surprised if the upper head has been wrecked -- the loading mechanism
jammed a while ago. I stripped it, re-lubricated the sliders and
reassembled it, but caught the top head when I was putting the top plate
(with the pin that opens the disc shutter) back in.
The head that's having issues appears to be "side 0" if that means
anything (my copy of the ECMA 3.5in floppy standards is "missing" ATM,
and I can't remember if that's the upper or lower head).
The upper head -- the one that points down -- is side 1. Side 0 is the
underside of the disk. The way to rememebr that is that the single-head
drive has the lower head only with a preasure pad on the moveable part of
the arm. And yes, single-head 3.5" drives do exist (as for that matter to
40 cylinder ones -- 67.5 tpi)/
TBH, the timing histogram from the Sony drive's upper head looks like
Do you mean 'upper head' or 'side 0 head' here?
noise. The timing histogram from the same disc in the
Citizen drive (see
An open-circuit head will produce noise, as will anything that causes it
not to be connected to the read amplifier.
This one has two flexiprint cables with five pins
each. No components on
the flexi unless they're hidden inside the plastic body of the head
mountings.
That;s normal for later drives. The switching components are on the PCB.
That Sony model number sounds somewhat familiar
to me. Is it a normal-size
(half-height, techniclly 3.5" unit with a logic board iwth 2 large PQFPs
on it (one for the analouge circuitry and one for the digital circuitry)?
It's 1-in high, with an 80-pin QFP labelled "SONY / CXA1803Q / JAPAN /
429A94K", a 32-pin TSSOP labelled "BA6489FS / 435 148" and a 20-pin SOIC
labelled "NEC JAPAN / D16803 / 9423F7" on the logic board. Those 2 seem
inconsistent. The first says that TRK00 is never asserted,
the latter gices a time when it is. Which is it?
It turned out to be a logic bug in the FPGA -- the nSTEP output wasn't
being set high/inactive when the seek had completed (though it was being
set high to produce the pulses during the seek). In other words, it
looked like this:
__ __ __
STEP ___| |__| |__| |____________
When I wanted this:
__ __ ____________
STEP ...___| |__| |__|
Added the missing assignment and now it works fine. Interesting that the
Sony drive didn't care about this, yet the Citizen apparently locked up.