7 Sep
1999
7 Sep
'99
3:15 p.m.
Here's another installment in the ongoing HP7900A drive saga (yes, it's a
plea for advice and/or sympathy <grin>)
Installed new (refurbed) lower heads and new lower platter. Recleaned inside
of drive. Powered up, put in new removable cartridge. Hit load switch and
waited 25 seconds, then hit unload. Did this a few times (the blowers and
drive spins up, but the heads don't load for 30 seconds - did this to get
any remaining particles out). Removed cartridge, powered down, removed
covers and reinspected everything inside. All looked well (including heads,
which were fully retracted).
So, this time I powered up and hit load. Waited 30 seconds, heard the heads
move out to cylinder 0. Ran drive like this for about 3 minutes, no problem.
Hit unload. When I removed the removable cartridge, I noticed the heads
weren't quite retracted all the way. They were well off the media, but not
all the way back home (the heads weren't touching each other, but they were
close). Manually pushed the heads back, rechecked everything I could find.
Repowered up the drive, after 30 seconds the heads loaded. Drive ready lite
comes on and ran for about 15 minutes. No HDI sounds at all. I was elated.
Hit unload, and after about 20 seconds heard very soft HDI. This time I left
the cartridge in, powered everything off, removed the covers, and this time
the heads weren't retracted at all. They were sitting right on the media.
Strange thing is, there's no marks on the media, the lower heads I replaced
look pristine, and the upper heads have only the very slightest indication
of oxide.
Gee - perhaps this is why the drive originally had a head crash before I got
it? I've been through the "theory of operation" text and flowcharts.
Several
things confuse me. First, I thought that hitting the unload switch was
pretty much of an immediate voice coil retraction - I didn't think this went
through all the normal logic circuits. Second, the coil can't be completely
shot I wouldn't think, because as I understand it the drive ready light
won't even come on unless the positioner moves out to cyl 0 correctly.
Before I replaced the heads and media, I don't THINK I had this problem, I
think I would have noticed if the heads weren't retracting before. But, I
can't imagine that anything I did related to replacing the lower head set
and the lower platter would have anything to do with this. Input anyone?????
TIA!
Jay West
7 Sep
7 Sep
3:53 p.m.
At 10:15 PM 09/07/1999 -0500, you wrote:
Here's another installment in the ongoing HP7900A
drive saga (yes, it's a
plea for advice and/or sympathy <grin>)
...
Hit unload, and after about 20 seconds heard very soft HDI. This time I left
the cartridge in, powered everything off, removed the covers, and this time
the heads weren't retracted at all. They were sitting right on the media.
Strange thing is, there's no marks on the media, the lower heads I replaced
look pristine, and the upper heads have only the very slightest indication
of oxide.
...
Gee - perhaps this is why the drive originally had a head crash before I got
it? I've been through the "theory of operation" text and flowcharts.
Several
things confuse me. First, I thought that hitting the unload switch was
pretty much of an immediate voice coil retraction - I didn't think this went
through all the normal logic circuits. Second, the coil can't be completely
shot I wouldn't think, because as I understand it the drive ready light
won't even come on unless the positioner moves out to cyl 0 correctly.
Before I replaced the heads and media, I don't THINK I had this problem, I
think I would have noticed if the heads weren't retracting before. But, I
can't imagine that anything I did related to replacing the lower head set
and the lower platter would have anything to do with this. Input anyone?????
Well... not having (personally) worked on the HP drives, but having done a
fair deal of time on CDC cartridge drives which sound functionally similar,
I'll offer a couple of thoughts...
You are basically correct in your observation that 'head retract' does not
usually go through the 'normal logic'. In the CDC drives at least, the
head retract circuit is the same as the 'emergency' retract circuit (i.e.
get the heads OFF in the event of a power failure).
In brief, the circuit is this:
Keeping in mind that it takes more force on the positioner to pull the
heads back up the load/unload ramp, the standard drive circuit does not do it.
When the drive is powered up, a relay is engaged which opens a circuit to
the positional coil, allowing the normal drive circuit to function.
When you hit unload, or the power fails, this relay drops out which
connects a large(ish) capacitor (which has been charging all this time) to
the coil, and WHOMP! You unload the heads! (the discharge rate of the
'cap also ensures that the coil does not bounce back off of the stops)
Really! It is designed this way!
So... (if the HP drive uses a similar system) you look for: An oddly out
of place looking (heavier than the norm) cable coming to the positioner
coil, a large(ish) relay with good sized contacts, and a large electrolytic
(metal can) capacitor!
These should all be connected together in a fairly logical fashion...
A frequent cause of 'retract failure', especially after the unit has been
aligned/serviced/ heads replaced, is the failure of the technician to
reconnect the unload system!
Also... burned relay contacts, bad relay, bad capacitor, failed charging
circuit...
It is actually part of the stated proceedure to disable the unload system
when you are working on the unit, since there are a number of conditions
that can trigger it (spindle speed fault, positioner overrun, off-track
fault, etc...), and you only have to have your hand behind the head
carriage ONCE (especially a large one like a CDC Phoenix) when that system
triggers to ensure that you will NEVER do it again! (BTDT!)
FWIW...
-jim
---
jimw(a)computergarage.org
The Computer Garage - http://www.computergarage.org
Computer Garage Fax - (503) 646-0174
6:58 p.m.
Jim, thanks for those comments. I have a Phoenix drive that has crashed
and I've been thinking about trying to take a look at it. I've been
following the 7900 thread especially to get an idea of what I might be in
for.
On Tue, 7 Sep 1999, James Willing wrote:
At 10:15 PM 09/07/1999 -0500, you wrote:
M. K. Peirce
Rhode Island Computer Museum, Inc.
215 Shady Lea Road,
North Kingstown, RI 02852
"Casta est qui nemo rogavit."
- Ovid
Here's another installment in the ongoing
HP7900A drive saga (yes, it's a
plea for advice and/or sympathy <grin>)
...
Hit unload, and after about 20 seconds heard very soft HDI. This time I left
the cartridge in, powered everything off, removed the covers, and this time
the heads weren't retracted at all. They were sitting right on the media.
Strange thing is, there's no marks on the media, the lower heads I replaced
look pristine, and the upper heads have only the very slightest indication
of oxide.
...
Gee - perhaps this is why the drive originally had a head crash before I got
it? I've been through the "theory of operation" text and flowcharts.
Several
things confuse me. First, I thought that hitting the unload switch was
pretty much of an immediate voice coil retraction - I didn't think this went
through all the normal logic circuits. Second, the coil can't be completely
shot I wouldn't think, because as I understand it the drive ready light
won't even come on unless the positioner moves out to cyl 0 correctly.
Before I replaced the heads and media, I don't THINK I had this problem, I
think I would have noticed if the heads weren't retracting before. But, I
can't imagine that anything I did related to replacing the lower head set
and the lower platter would have anything to do with this. Input anyone?????
Well... not having (personally) worked on the HP drives, but having done a
fair deal of time on CDC cartridge drives which sound functionally similar,
I'll offer a couple of thoughts...
You are basically correct in your observation that 'head retract' does not
usually go through the 'normal logic'. In the CDC drives at least, the
head retract circuit is the same as the 'emergency' retract circuit (i.e.
get the heads OFF in the event of a power failure).
In brief, the circuit is this:
Keeping in mind that it takes more force on the positioner to pull the
heads back up the load/unload ramp, the standard drive circuit does not do it.
When the drive is powered up, a relay is engaged which opens a circuit to
the positional coil, allowing the normal drive circuit to function.
When you hit unload, or the power fails, this relay drops out which
connects a large(ish) capacitor (which has been charging all this time) to
the coil, and WHOMP! You unload the heads! (the discharge rate of the
'cap also ensures that the coil does not bounce back off of the stops)
Really! It is designed this way!
So... (if the HP drive uses a similar system) you look for: An oddly out
of place looking (heavier than the norm) cable coming to the positioner
coil, a large(ish) relay with good sized contacts, and a large electrolytic
(metal can) capacitor!
These should all be connected together in a fairly logical fashion...
A frequent cause of 'retract failure', especially after the unit has been
aligned/serviced/ heads replaced, is the failure of the technician to
reconnect the unload system!
Also... burned relay contacts, bad relay, bad capacitor, failed charging
circuit...
It is actually part of the stated proceedure to disable the unload system
when you are working on the unit, since there are a number of conditions
that can trigger it (spindle speed fault, positioner overrun, off-track
fault, etc...), and you only have to have your hand behind the head
carriage ONCE (especially a large one like a CDC Phoenix) when that system
triggers to ensure that you will NEVER do it again! (BTDT!)
FWIW...
-jim
---
jimw(a)computergarage.org
The Computer Garage - http://www.computergarage.org
Computer Garage Fax - (503) 646-0174
6:42 p.m.
Jay,
This is just a shot in the dark but I used to work on large voice coil
drives and they used a Saft NiCad battery to retract the heads. The %$^%&^%
Saft batteries were no good and we often lost disks and heads due to them
not retracting. In theory, the battery was there to supply power and
retract the heads in case the drive lost AC power but they cut corners and
also used it retract the heads even when AC power was still available. So
much for theory! Look around carefully and see if it might have a battery
or possible even a large capacitor in it and check it carefully.
Joe
At 10:15 PM 9/7/99 -0500, you wrote:
Here's another installment in the ongoing HP7900A
drive saga (yes, it's a
plea for advice and/or sympathy <grin>)
Installed new (refurbed) lower heads and new lower platter. Recleaned inside
of drive. Powered up, put in new removable cartridge. Hit load switch and
waited 25 seconds, then hit unload. Did this a few times (the blowers and
drive spins up, but the heads don't load for 30 seconds - did this to get
any remaining particles out). Removed cartridge, powered down, removed
covers and reinspected everything inside. All looked well (including heads,
which were fully retracted).
So, this time I powered up and hit load. Waited 30 seconds, heard the heads
move out to cylinder 0. Ran drive like this for about 3 minutes, no problem.
Hit unload. When I removed the removable cartridge, I noticed the heads
weren't quite retracted all the way. They were well off the media, but not
all the way back home (the heads weren't touching each other, but they were
close). Manually pushed the heads back, rechecked everything I could find.
Repowered up the drive, after 30 seconds the heads loaded. Drive ready lite
comes on and ran for about 15 minutes. No HDI sounds at all. I was elated.
Hit unload, and after about 20 seconds heard very soft HDI. This time I left
the cartridge in, powered everything off, removed the covers, and this time
the heads weren't retracted at all. They were sitting right on the media.
Strange thing is, there's no marks on the media, the lower heads I replaced
look pristine, and the upper heads have only the very slightest indication
of oxide.
Gee - perhaps this is why the drive originally had a head crash before I got
it? I've been through the "theory of operation" text and flowcharts.
Several
things confuse me. First, I thought that hitting the unload switch was
pretty much of an immediate voice coil retraction - I didn't think this went
through all the normal logic circuits. Second, the coil can't be completely
shot I wouldn't think, because as I understand it the drive ready light
won't even come on unless the positioner moves out to cyl 0 correctly.
Before I replaced the heads and media, I don't THINK I had this problem, I
think I would have noticed if the heads weren't retracting before. But, I
can't imagine that anything I did related to replacing the lower head set
and the lower platter would have anything to do with this. Input anyone?????
TIA!
Jay West
8 Sep
8 Sep
5:52 a.m.
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18 Sep
18 Sep
12:27 p.m.
Jay, have you checked the mechanics? I have a similar vintage HP drive (HP
2870A - OEM was Iomec) which had
a mechanical spring-loaded mechanism for unloading the heads. I found that
my was pretty gummy with old
lubricant, and had to clean it up / degrease it before it would operate
properly. (Fortunately for me, I recognized
this _before_ I loaded the heads the first time.
Jay Jaeger
So, this time I powered up and hit load. Waited 30 seconds, heard the heads
move out to cylinder 0. Ran drive like this for about 3 minutes, no problem.
Hit unload. When I removed the removable cartridge, I noticed the heads
weren't quite retracted all the way. They were well off the media, but not
all the way back home (the heads weren't touching each other, but they were
close). Manually pushed the heads back, rechecked everything I could find.
Repowered up the drive, after 30 seconds the heads loaded. Drive ready lite
comes on and ran for about 15 minutes. No HDI sounds at all. I was elated.
Hit unload, and after about 20 seconds heard very soft HDI. This time I left
the cartridge in, powered everything off, removed the covers, and this time
the heads weren't retracted at all. They were sitting right on the media.
Strange thing is, there's no marks on the media, the lower heads I replaced
look pristine, and the upper heads have only the very slightest indication
of oxide.
---
Jay R. Jaeger The Computer Collection
Jay.Jaeger(a)msn.fullfeed.com visit http://www.msn.fullfeed.com/~cube
24 Sep
24 Sep
2:05 a.m.
New subject: 7900A drive: 1 , Me - 0 also - 7908 available possibly? + email address change...
Oh, and by the way, the score seems to be 7900A: 1, me: 0.9 now <grin>
You wrote....
Jay, have you checked the mechanics? I have a similar
vintage HP drive
(HP
2870A - OEM was Iomec) which had
a mechanical spring-loaded mechanism for unloading the heads. I found
that
my was pretty gummy with old
lubricant, and had to clean it up / degrease it before it would operate
properly
The unload mechanism on the 7900A is entirely electrical, not mechanical.
But - thanks for the tip!
(Fortunately for me, I recognized
this _before_ I loaded the heads the first time.
I sincerely wish I had been so lucky! (then I wouldn't be faced with getting
the top heads recontoured now) :)
I'm taking vacation all next week, so I plan to revisit the 7900A and
hopefully finish it off. One thing I'm wrestling with now - I need to
thoroughly re-clean the inside of the drive. Any cloth I've tried around the
house doesn't seem to be "lint-free", and leaves many little threads and
stuff behind. Has anyone found any common cloths that don't do this? I was
wondering about an old undershirt, etc. Ideas?
Also - I had heard there might be a 7908 drive available from a private
email (NOT for sure yet). If so, anyone interested? Of course, again - if
anyone knows where I can get another 7900A or two, PLEASE let me know!
Finally, I just got around to setting up a second email address for personal
mail rather than business mail. They are:
Work email: jlwest(a)tseinc.com
Home email: west(a)tseinc.com
If anyone has me in their addressbook, please change the jlwest address to
west. I only check the home email when I'm at home though, so if you want a
response during the day feel free to use the old jlwest address.
Thanks!
Jay West
4:01 a.m.
New subject: 7900A drive: 1 , Me - 0 also - 7908 available possibly? + email address change...
On Fri, 24 Sep 1999, Jay West wrote:
stuff behind. Has anyone found any common cloths that
don't do this? I was
wondering about an old undershirt, etc. Ideas?
I usually use old white, cotton t-shirts for this and they work pretty
well. I bought a package of special lint-free, "dust-magnet" cloths for
photographic use, which work well on drive heads, etc.
Aaron
9221
days inactive
9238
days old
7 comments
7 participants
participants (7)
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af-list＠lafleur.wfi-inc.com -
ard＠p850ug1.demon.co.uk -
at258＠osfn.org -
cube＠msn.fullfeed.com -
jimw＠agora.rdrop.com -
jlwest＠tseinc.com -
rigdonj＠intellistar.net