Re: 8 inch floppy head pad adjustment

[Chris Zach via cctalk]

Thanks Jeff! Yep, one of the odd things about 8 inch floppies is they 
are always spinning (at least on RX01/02 drives) and thus the disc is 
always turning in the sleeve, and if the head is engaged it will wear down.


What they do is have a head on one side, and on the other is the 
solenoid with the shoe. Mine was way too low, so the head was basically 
always pressed into the disc. It's better now, and doesn't seem to be 
doing damage.


Sort of. One thing I am noticing is a lot of these disks came from the 
old Solarex plant. They have a lot of "data" that is probably test 
results from the wafer cutting systems and I'm debating keeping it. More 
to the point most of the disks are RX02 format so I can't read them with 
this RX02 running in RX01 mode (until I manage to fix a UNibus pdp111 
here, that's either the 11/24 or the 11/05. But the 11/05 might only 
have 24kw of memory so we'll see)


Anyway the bigger problem is this stuff was on the plant floor. Where 
the panels were cut. Which means there is silicon dust *everywhere*. 
Remember when my RL02 heads crashed? That was because the RL02 drive's 
filter was *clogged* with dust to the point where the heads couldn't fly 
and were wedge shaped from wear. Pretty sad. But for the floppies I can 
see that many of them have concentric rings in the data areas from where 
the silicon dust got on them and sliced into the data rings. Fortunately 
the RX02 didn't come from there, but since the silicon is embedded into 
the jackets it just wrecks the floppies the more they spin. So fire up 
and get the data fast is probably what I will have to do. We'll see.


However I do now have three RX01 disks with no errors, and one with 
about 20 errors due to a ding in the disk. I've tested them with DX0 to 
the point where I am happy it's reliable, and have made one a BRUSYS 
boot up floppy with RSX11M's VMR utility so I can boot from floppy and 
back up the system on the TK50 drive. Better than blowing a whole tape 
with nothing but BRUSYS. The other floppy I'll use to see if I can get 
the PDT11/150 working, I don't know the shape of that things heads 
either but I do know disk 2 is down. Oh well, never dull...


It's getting cooler outside, so I can get back to work on these systems. 
The VT52 is still working very well with no hum or whistle, the repair 
of the -12v supply seems to be holding out well.


CZ
On 10/9/2020 4:02 PM, Jeffrey S. Worley wrote:
I've not worked on 8" floppy drives, but have on tons of 5.25" 
single-sided drives.  Older single-sided ones (usually 35-track from the 
70's) had load solenoids for the pressure pads, as with a double-sided unit.


The pad is to provide good contact between the media surface and the 
head beneath.  I think older media must have ablated more than 
latter-day media does, as it is rare to find a single-sided 5.25" drive 
with a load solenoid.  The pad is always in contact whenever the drive 
door is closed.  Double-sided drives of course retained the head-load 
solenoid for some years, but eventually those were done away with.  So, 
I think that unless you are using a drive 24/7, a pad in contact with 
the disk should not be a serious concern.  That the pad IS properly in 
contact is important of course, and pads should be inspected to see that 
there is enough 'meat' left on them to provide the pressure needed.  Aft 
of the pad, at the base of the head-sled pressure arm is a notch into 
which the end of the spring rides.  Close examination of the sled will 
probably show some higher and lower notches into which you can move the 
end of the spring, to provide more or less pressure as needed, to tune a 
particular drive.


In the old days, someone running a drive on a BBS or other heavy 
application might wear a pad out.  We'd just steal one from a cassette 
tape and stick it on the arm.  The cassette tape pad was square and the 
originals were round, but it never seemed to make any difference.  These 
days there are no cassettes floating around to cannibalize, so I buy 
felt pads for furniture from Amazon, trim them with a razor and stick 
them on a drive I'm refurbishing.  Atari, Commodore, Tandy...  Many of 
the 80's 8-bits used this very scheme on their single-sided drives and 
this solution is good for all of them.


I had someone insist to me recently that the felt pads I was buying were 
acrylic and the originals were Rabbit Hair and that it was crucial that 
the replacements be made of rabbit hair.  In practice, and that is 40 
years of practice, any old pad will do just fine.  If it looks like the 
right thing it will serve the purpose.   Just pick off  the old nub of a 
pad and stick on your newly cut one and go.


Common faults I've been noticing are that disk drives made in the 70's, 
80's, and 90's are failing in common ways.  I attribute these failures 
mostly to lack of lubrication.  After 30 years they get a bit gummy and 
the actuators have to work harder to move the head sled, which puts a 

Re: 8 inch floppy head pad adjustment

[Paul Berger via cctalk]

The big difference is most 8" drives had AC motors that turned the 
spindle all the time so if a diskette drive was loaded it would turn all 
the time and if the head(s) where loaded it would wear a groove in the 
media, hence the head load solenoid.   Most 5.25 and smaller drives have 
a DC motor that is only turned on when you are about to read or write 
the diskette so leaving the heads loaded is less of an issue.


Paul.

On 2020-10-09 5:02 p.m., Jeffrey S. Worley via cctalk wrote:

I've not worked on 8" floppy drives, but have on tons of 5.25" single-
sided drives.  Older single-sided ones (usually 35-track from the 70's)
had load solenoids for the pressure pads, as with a double-sided unit.

The pad is to provide good contact between the media surface and the
head beneath.  I think older media must have ablated more than latter-
day media does, as it is rare to find a single-sided 5.25" drive with a
load solenoid.  The pad is always in contact whenever the drive door is
closed.  Double-sided drives of course retained the head-load solenoid
for some years, but eventually those were done away with.  So, I think
that unless you are using a drive 24/7, a pad in contact with the disk
should not be a serious concern.  That the pad IS properly in contact
is important of course, and pads should be inspected to see that there
is enough 'meat' left on them to provide the pressure needed.  Aft of
the pad, at the base of the head-sled pressure arm is a notch into
which the end of the spring rides.  Close examination of the sled will
probably show some higher and lower notches into which you can move the
end of the spring, to provide more or less pressure as needed, to tune
a particular drive.

In the old days, someone running a drive on a BBS or other heavy
application might wear a pad out.  We'd just steal one from a cassette
tape and stick it on the arm.  The cassette tape pad was square and the
originals were round, but it never seemed to make any difference.
  These days there are no cassettes floating around to cannibalize, so I
buy felt pads for furniture from Amazon, trim them with a razor and
stick them on a drive I'm refurbishing.  Atari, Commodore, Tandy...
  Many of the 80's 8-bits used this very scheme on their single-sided
drives and this solution is good for all of them.

I had someone insist to me recently that the felt pads I was buying
were acrylic and the originals were Rabbit Hair and that it was crucial
that the replacements be made of rabbit hair.  In practice, and that is
40 years of practice, any old pad will do just fine.  If it looks like
the right thing it will serve the purpose.   Just pick off  the old nub
of a pad and stick on your newly cut one and go.

Common faults I've been noticing are that disk drives made in the 70's,
80's, and 90's are failing in common ways.  I attribute these failures
mostly to lack of lubrication.  After 30 years they get a bit gummy and
the actuators have to work harder to move the head sled, which puts a
greater load on the darlington drivers which power the actuators, which
causes the drivers to fail.  Replacing the drivers will often restore
the drive to working order, but they will fail again in short order if
the original probelm is not resolved.  I simply clean the rails and
stepper bands, touch a little wd40 to the rails to free the head sled,
cycle the head back and forth a buncha times manually to exercise it
and distribute the lubricant, then follow that will a little white
lithium grease for a longer-lived lube.  Not only will the drive run
better and a lot quieter when lubricated, the loads on the actuators
and their associated electronics are greatly reduced, making for a
like-new drive.

The second thing that is happening quite often is electrolytic
capacitors are failing, leaking or not.  I had a pair of drives the
other day which made quite a racket when spinning free even without
media installed.  Replacing the electrolytics on the spindle motor's
board got rid of the noise and made it possible to properly tune the
RPM's, which had been just all over the map.

best,

Jeff

Re: 8 inch floppy head pad adjustment

[Jeffrey S. Worley via cctalk]

I've not worked on 8" floppy drives, but have on tons of 5.25" single-
sided drives.  Older single-sided ones (usually 35-track from the 70's)
had load solenoids for the pressure pads, as with a double-sided unit.

The pad is to provide good contact between the media surface and the
head beneath.  I think older media must have ablated more than latter-
day media does, as it is rare to find a single-sided 5.25" drive with a
load solenoid.  The pad is always in contact whenever the drive door is
closed.  Double-sided drives of course retained the head-load solenoid
for some years, but eventually those were done away with.  So, I think
that unless you are using a drive 24/7, a pad in contact with the disk
should not be a serious concern.  That the pad IS properly in contact
is important of course, and pads should be inspected to see that there
is enough 'meat' left on them to provide the pressure needed.  Aft of
the pad, at the base of the head-sled pressure arm is a notch into
which the end of the spring rides.  Close examination of the sled will
probably show some higher and lower notches into which you can move the
end of the spring, to provide more or less pressure as needed, to tune
a particular drive.

In the old days, someone running a drive on a BBS or other heavy
application might wear a pad out.  We'd just steal one from a cassette
tape and stick it on the arm.  The cassette tape pad was square and the
originals were round, but it never seemed to make any difference.
 These days there are no cassettes floating around to cannibalize, so I
buy felt pads for furniture from Amazon, trim them with a razor and
stick them on a drive I'm refurbishing.  Atari, Commodore, Tandy...
 Many of the 80's 8-bits used this very scheme on their single-sided
drives and this solution is good for all of them.

I had someone insist to me recently that the felt pads I was buying
were acrylic and the originals were Rabbit Hair and that it was crucial
that the replacements be made of rabbit hair.  In practice, and that is
40 years of practice, any old pad will do just fine.  If it looks like
the right thing it will serve the purpose.   Just pick off  the old nub
of a pad and stick on your newly cut one and go.

Common faults I've been noticing are that disk drives made in the 70's,
80's, and 90's are failing in common ways.  I attribute these failures
mostly to lack of lubrication.  After 30 years they get a bit gummy and
the actuators have to work harder to move the head sled, which puts a
greater load on the darlington drivers which power the actuators, which
causes the drivers to fail.  Replacing the drivers will often restore
the drive to working order, but they will fail again in short order if
the original probelm is not resolved.  I simply clean the rails and
stepper bands, touch a little wd40 to the rails to free the head sled,
cycle the head back and forth a buncha times manually to exercise it
and distribute the lubricant, then follow that will a little white
lithium grease for a longer-lived lube.  Not only will the drive run
better and a lot quieter when lubricated, the loads on the actuators
and their associated electronics are greatly reduced, making for a
like-new drive.

The second thing that is happening quite often is electrolytic
capacitors are failing, leaking or not.  I had a pair of drives the
other day which made quite a racket when spinning free even without
media installed.  Replacing the electrolytics on the spindle motor's
board got rid of the noise and made it possible to properly tune the
RPM's, which had been just all over the map.

best,

Jeff

Re: 8 inch floppy head pad adjustment

[Chris Zach via cctalk]

Ok, thanks! My guess is without pressure the disk just floats along the 
head, the problem I was running into was that the disks would get 
grooves in them after running in the floppy for awhile and the head 
would get dirty. Probably because the head was pressed against the same 
track constantly as the pad was always down.


Finishing up the cleaning today, will then check the system and see what 
works


C


On 10/7/2020 9:21 AM, dwight wrote:
Look at the Shugart 800 manual. It shows a similar adjustment for the 
pad. The head may still touch the disk though when the pad is lifted on 
the 800. Maybe not a good idea but how it was done. Do make sure the pad 
is clean and flat.

Re: 8 inch floppy head pad adjustment

[dwight via cctalk]

Look at the Shugart 800 manual. It shows a similar adjustment for the pad. The 
head may still touch the disk though when the pad is lifted on the 800. Maybe 
not a good idea but how it was done. Do make sure the pad is clean and flat.
Dwight


From: cctalk  on behalf of Chris Zach via cctalk 

Sent: Tuesday, October 6, 2020 7:14 PM
To: CCTalk mailing list 
Subject: 8 inch floppy head pad adjustment

Working on cleaning up my RX02 drives: I've taken the 8 inch floppy
units out of the case/chassis and have been cleaning dust and such off
the whole assemblies.

One thing I noticed: There is a pad opposite the head that comes down
when a solenoid is energized to provide pressure against the read head.
Makes sense, it also has a pad that presses against the floppy disc
itself, probably to keep it from jittering. However I noticed on both
heads that the bracket is adjusted all the way down. This means that
even when the solenoid is not energized the head pad is pressing against
the disk and pushing the disk against the head.

Is this normal? I would think this would result in the floppy always
being pressed against the head and quickly wearing out the disk. The
whole point is to let the disk float against the head, only letting the
pad push things into contact when doing a read.

Do I have this right, and is adjusting that that assembly proper when
the pad puck is not touching the disk when up, but is touching it when down?

C