6 Nov
2010
6 Nov
'10
5:46 p.m.
On 06/11/10 20:03, Tony Duell wrote:
It does sound like head or ASIC problems...
:(
Both of which would require a supply of Unobtainium and Magic Smoke (not
to mention the fabled Magic Smoke Inserter) to repair or replace. I dare
say these drives are going to become mechanical parts mules...
I have a Fluke 25 that lives in the cupboard, but I'm too lazy to wheel
my chair over to the cupboard to get it :)
The Agilent is downstairs. I'm trying to figure out why DiscFerret #2 is
having power-backfeed issues (the SENSE line from the USB port is
backfeeding onto +3V3 and Blowing Stuff Up.. and I've ruled out a
hard-short).
Aha...This remionds me ao a character I saw at a
couple of radio rallies
many yearsa ago. He had a pile of working hard drives. And another pile
of ''untensted' hard drives. Hmmm...
Read as: "I've tested all of these, but I'm selling the broken ones as
'untested'."
Then you get the fiercely honest ones -- I approached a seller at a
radio rally, and asked about some VRLA batteries he was selling.
"Ah, they're only a couple of months old -- brand new. Serial number's
here, and manufacture date here. Charged them up half-way the other day,
hang on, I've got a multimeter here somewhere.... Oh, and I'll wire a
car headlamp over one if you'd like to see it running under load..."
I wonder if theprevious owner plugged them into a PC
power supply and
then discovered that either they didn't work, or somebody told him he'd
probably done some daamge, so you ended up with them
Indeed. I've got a lead on a pair of double-sided drives from a PCW9512.
They're basically the same drive design, but without the write protect
sense pin (optical sensing!), a white front panel and a slightly
different mounting cage.
Fingers crossed...
Anything on TP1,2 on the drive PCB? Those are the
differential outputs of
the read amplifier, used for head alignment.
Nope, nothing on either. On the to-do
list (it's a bit late to be getting out the DMM at this
time of day!)
You put the DMM away? That suprises me ;-) I think I would start by checking the pin voltages on
the ASIC, and in
particular see what the head cnetre-taps are doing.
-- In write mode --
I'm seeing around 2V on all three pins of the head -- 'top', 'bottom'
and the centre tap. If I switch to AC coupling, 200mV/div, I see what
looks like a very noisy sine wave on the centre tap, and then the coils
have the same noisy sine, plus an alternating pulse. If I subtract the
CT from either coil, I can see the magnetic pulses. These look like the
0-180deg (positive going) part of a sinewave, then a gap, then the
180-360deg (negative going) part.
-- In read mode --
Not a sausage at 200mV. Dropping to 50mV/div, I can see a heck of a lot
of noise, but nothing that looks remotely like the 125kHz data I fed it.
There's nothing interesting on TP1, TP2 and TP3 either. With drive stopped:
TP1 -- 258.45kHz sine, ~200mV amplitude
TP2 -- same sine wave, 180 degrees out of phase
TP3 -- ground
Adding the two channels together gets me a flat line with a bit of
noise. Subtracting (per the instructions in the service manual) gets me
a 400mV pk-pk sine...
It's as if the ASIC were oscillating internally...
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/