....aaaand it worked and still wasn't enough :/
The super-glue seems to be holding ok. I didn't test it with much force
obviously but enough to feel like it was at least stronger than what it
should take to spin the disk.
And the disk does spin. You can hear the hub slide and snick into place
and you can see the exposed floppy surface wave a little while trying to
list a directory.
But it still fails with "no index signal"
And after those failed read attempts, I can still feel that the hub has
not broken loose from the shaft. With the unit all assembled but just
the top cover off, no disk inserted, I can get my finger through the
head travel opening on top and reach the hub and rotate it back & forth
a little and feel the inertia of the pulley, belt, & motor, and verify
that it is still locked to the shaft, not slipping.
Oh well!
Maybe I'll get to play with my new hacked rigol hdo804 after all.
(Anyone want a practically unused ds1054z also hacked to enable all
features and upgrades? (memory, serial decoders, 100mhz) Say $200 even,
we split the shipping, and includes a rigol carry case which was
something like 50 or 70 itself. It probably doesn't have 10 hours of
on-time since I got it new from tequipment a few years ago.)
At least no index pulse sounds simpler to track down than some actual
signal path problem.
One thing I can try easy for starters is just swap the drive mech & pcb
between 2 units and see which way the problem travels, does it stay with
the mech or stay with the board? Only for testing, I wouldn't lose the
original factory pairing between boards & mechs.
--
bkw
On 3/21/24 09:40, [email protected] wrote:
That is an uncommon failure for a TPDD. I have seen that same type of failure
on scads of other plastic parts pressed onto metal shafts. The plastic shrinks
as it ages, the metal does not and eventually the plastic hub cracks.
It is hard to tell, but it looks like the hub is a separate piece from the
pulley and staked in place. Perhaps they are two different materials?
I suspect the only way to fix this would be to bore out the hub at least 1-2mm
and glue in a compatible piece of plastic with an ID suitable for pressing onto
the shaft and an OD that is a tight fit into the bored hole.
Jeff Birt
-----Original Message-----
From: M100 <[email protected]> On Behalf Of Brian K. White
Sent: Thursday, March 21, 2024 3:17 AM
To: [email protected]
Subject: [M100] unexpected tpdd failure mode
Encountered an unexpected way for a tpdd to fail.
I have a Purple Computing drive I got a couple years ago that never worked. But
it almost worked. The cpu and sensors and motor control actually all worked
fine. You can send it commands and it responds correctly, you can read the
state of the sensors, you can make both motors run on command. The only problem
was actually reading or writing data never worked.
I always assumed that it was going to be some exotic problem with the head read
amplifier circuit or something like that that will require the scope to hunt
down.
I was in the process of swapping the guts out from a parts-only busted up tpdd1
from ebay and along the way the big pulley and main shaft basically fell out.
So the problem all along was the disk grabber hub was spinning freely loose on
the main shaft. Turns out the disk grabber hub is plastic and just pressed onto
the shaft, and the plastic had cracked around the shaft. Overall the hub is
still whole, just the bore is no longer an interference fit, it's now merely an
exact fit.
It's hard to see this problem because all the parts you can see are working
fine. There's almost no way to see any of the hub or the disk when it's working
to see that it's not spinning when the big pulley is spinning.
The way you can tell is if the big pulley can be pulled out at all.
Normally it can spin but not pull in/out at all.
I don't know what's a good way to glue the hub back to the shaft. It's a smooth
polished bearing surface shaft, so I tried super glue but I expect it'll just
break free as soon as I try to use it, but I'll let it sit for a day before I
try.
Here's a couple pics of the parts since you can't normally see these parts.
The main spindle has a single ball bearing and a plain bushing or possibly
sintered bearing. The brass part in the middle is both the holder for the ball
bearing on the disk side, and the plain bushing bearing on the belt side.
https://photos.app.goo.gl/QbirJowcGEEdV3xb9
--
bkw
--
bkw
