H
Homer J Simpson
- Jan 1, 1970
- 0
"What holds 10 Mb of data or a pint of sea water? An IBM hard drive!"
(Someone exchanged them for good ones and dumped the duds as a reef).
"What holds 10 Mb of data or a pint of sea water? An IBM hard drive!"
(Someone exchanged them for good ones and dumped the duds as a reef).
M
Michael A. Terrell
- Jan 1, 1970
- 0
Lostgallifreyan said:
What models were they? i have a pile of dead hard drives, and I
believe there are several IBM . I know I saw a dead 15 GB IBM EIDE
drive the other day.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
M
Michael A. Terrell
- Jan 1, 1970
- 0
Jan said:
Not to mention punched card sorting machines, and made those damned
school clocks that jumped omce a second while you were trying to
concentrate.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
L
Lostgallifreyan
- Jan 1, 1970
- 0
I think the 15 GB one was one of those that went bad in bulk. That said, it
was the 15 GB platters, the really notorious drive was the 75 GXP, they put
5 15 GB platters in it. Hitachi only recently dared to try 5 with the 400
GB drives. Those are ok though, I have two, with no problems at all. One on
backup offline, the other running all day, switched off for most nights,
and not the slightest complaint for several months so far.
There's a lot of smoke around that 'Deathstar' issue, but I managed to
ignore it, Hitachi had bought the line soon after, and changed things. If
your drives are from IBM's GXP75 range, they are probably afflicted, but if
they're from the Hitachi era, they almost certainly died of natural causes,
or violence.
I've had 9 Deskstars, and two died directly resulting from bad handling by
me, while moving hardware in a couple of very frustrating sessions. Caused
by problems that were not of those drive's making. Another was bought
secondhand, it has a controller problem that I never understood, probably
got zapped slightly by the previous owner. It won't co-operate with any
mainboard I have, but is currently doing very well in a FireWire enclosure
which it gets on well with. None of the other 6 ever dropped a byte unless
the OS crashed and borked something. Two of them are old 40 GB drives.
Long post, I know, but there is so much shouting and panic on the net about
these drives, that if the subject comes up, I have to counter it. Even if I
brought up the subject myself.
A
atec77
- Jan 1, 1970
- 0
I Sold and installed hundreds of the ibm drives with the "nic"Homer said:
"deathstars" all had a cooling fan and the number of failures was tiny ,
considering where I trade and how hot it is makes me wonder about the
reality of the claims about them
M
Mark
- Jan 1, 1970
- 0
why 50 Ohms?
see:
http://www.rfcafe.com/references/electrical/history_of_50_ohms.htm
or Goggle "why 50 ohms"
Also I have a question for the op...why do you want to BUY a ceramic
antenna when at these frequencies a small antenna can be printed
directly on the PWB for free....
Mark
,
see:
http://www.rfcafe.com/references/electrical/history_of_50_ohms.htm
or Goggle "why 50 ohms"
Also I have a question for the op...why do you want to BUY a ceramic
antenna when at these frequencies a small antenna can be printed
directly on the PWB for free....
Mark
,
P
PeteS
- Jan 1, 1970
- 0
Didi said:Pete,
which chipset are you using? I am in the process of NDA-ing (Marvell)
so I can
get some data to do probably the same which you are doing, so I wonder
(if you would/could discolse that, that is, privately or publically
All, I also wonder what the impact of a metal case would be on such an
antenna - one of the options I have is a metal (0.5mm thick brass)
case,
largish handheld size (with an opening for the TFT etc.).
Dimiter
Um... I happen to be using a chipset that has the same name as the
comics... email me privately.
Cheers
PeteS
P
PeteS
- Jan 1, 1970
- 0
Mark said:
Because a ceramic antenna can be done in a smaller space than the PCB
equivalent (I have indeed already done that for the GSM/GPRS unit) and
it can also be multipolarised, which is difficult with an ordinary PCB
antenna.
There *can* be reasons to buy these things
Cheers
PeteS
R
Rich Grise
- Jan 1, 1970
- 0
from: http://www.epanorama.net/documents/wiring/cable_impedance.html ,
about 2/3 way down the page:
"Why 50 ohm coax ?
Standard coaxial line impedance for r.f. power transmission in the U.S.
is almost exclusively 50 ohms. Why this value was chosen is given in a
paper presented by _Bird Electronic Corp._ Standard coaxial line
impedance for r.f. power transmission in the U.S. is almost exclusively
50 ohms. Why this value was chosen is given in a paper presented by Bird
Electronic Corp.
Different impedance values are optimum for different parameters. Maximum
power-carrying capability occurs at a diameter ratio of 1.65
corresponding to 30-ohms impedance. Optimum diameter ratio for voltage
breakdown is 2.7 corresponding to 60-ohms impedance (incidentally, the
standard impedance in many European countries).
Power carrying capacity on breakdown ignores current density which is
high at low impedances such as 30 ohms. Attenuation due to conductor
losses alone is almost 50% higher at that impedance than at the minimum
attenuation impedance of 77 ohms (diameter ratio 3.6). This ratio,
however, is limited to only one half maximum power of a 30-ohm line.
In the early days, microwave power was hard to come by and lines could
not be taxed to capacity. Therefore low attenuation was the overriding
factor leading to the selection of 77 (or 75) ohms as a standard. This
resulted in hardware of certain fixed dimensions. When low-loss
dielectric materials made the flexible line practical, the line
dimensions remained unchanged to permit mating with existing equipment.
The dielectric constant of polyethylene is 2.3. Impedance of a 77-ohm
air line is reduced to 51 ohms when filled with polyethylene. Fifty-one
ohms is still in use today though the standard for precision is 50 ohms.
The attenuation is minimum at 77 ohms; the breakdown voltage is maximum
at 60 ohms and the power-carrying capacity is maximum at 30 ohms.
Another thing which might have lead to 50 ohm coax is that if you take a
reasonable sized center conductor and put a insulator around that and
then put a shield around that and choose all the dimensions so that they
are convenient and mechanically look good, then the impedance will come
out at about 50 ohms. In order to raise the impedance, the center
conductor's diameter needs to be tiny with respect to the overall
cable's size. And in order to lower the impedance, the thickness of the
insulation between the inner conductor and the shield must be made very
thin. Since almost any coax that *looks* good for mechanical reasons
just happens to come out at close to 50 ohms anyway, there was a natural
tendency for standardization at exactly 50 ohms."
R
Rich Grise
- Jan 1, 1970
- 0
I think 52 ohms is the impedance at the bottom of a 1/4 wave whip with
a proper ground plane, or something like that.
Cheers!
Rich
K
krw
- Jan 1, 1970
- 0
....and 90ohm tried and coax inside the systems. There was a mix
though, some was 50ohm (mainly clocks, IIRC). The higher impedance
reduced power (and delta-I). Lower impedance is faster (higher
current to charge the load capacitance). They also used high-speed
dielectric (basically GoreTex).
K
krw
- Jan 1, 1970
- 0
Great technology and did exactly what was intended. Marketing was
another issue though. Do remember that IBM was about to circle the
drain in the early '90s. There was no money to promote OS/2, even
if M$' contract allowed it.
K
krw
- Jan 1, 1970
- 0
no- said:
I have a 75GXP (one of the supposedly bad ones) that's still going
strong. I have a 37GXP also, still spinning.
K
krw
- Jan 1, 1970
- 0
Probalbly (nothing to do with...). It's 377ohms, IIRC. Of course
there is 600ohm ladder-line (differential ;-).
A
atec77
- Jan 1, 1970
- 0
Nominally 52 , however bending the radials down produces a near perfectRich said:
match which depending on construction can often be 43 ohms or lower
impedance and the bending alters things for match but of course being
coax the feed is quite unbalanced . ( and a matched arial may not be
resonant)
Z
Zak
- Jan 1, 1970
- 0
Michael said:
There was a rumor that the IBM drives were failing because of the glue
of a QA sticker in the interior. Something that wasn't tested by
engineering. Anyone knwo of this is true?
That said I've taken apart a few 4 and 9 GB SCSI drives. One had a head
cash and you could see the glass of the platter. Nice. Another gave me a
big surprise when I opened it: the top platter had two crosses written
on it with a black marker. That side obviously did not have a head, and
manufacturing selected platters for this single-sided kind of use. But I
still feel the use of a black marker in a 'clean room' like this is odd.
Thomas
Z
Zak
- Jan 1, 1970
- 0
atec77 said:
There are no 'bad brands' I think, but bad batches. Like the controller
chips with bad epoxy causing a bunch of failures.
Once researched how a drive failed (tried to fix it), and it was the
spindle motor having a partial short. That drive (Seagate Medalist) had
layer of foam plastic on the outside of the PCB with a thin metal plate
over it. Sill, it wasn't the electronics that overheated - or would the
electronics have failed first, blowing up the motor, which then blew up
the swapped in board?
Thomas
L
Lostgallifreyan
- Jan 1, 1970
- 0
False. There's a duct formed between the two plates in the upper shell, the
breathe hole is there, it's the only way in unless you remove the screws,
and there's no sticker over it, there must NOT be one, for obvious reasons.
Even if there was, there's no way a small amount of resilient adhesive is
going to go right through along that duct after managing to pass a porous
membrane. Not even silicone grease can creep that well.
I've looked inside one of the Deskstars I broke with bad handling. No
stickers inside, nor any in any other brand of drive I've had. They'd never
risk leaving that much risk of contaminants inside where the platters and
heads are.
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