16 May
2010
16 May
'10
10:37 a.m.
I have posted before about an RD53 I am trying to get back to working order.
After unsticking the heads I thought I had a working disk as I have been
able to format it and do an image restore of the VMS installation media to
it. However, intermittently it has been failing. When this happens the heads
completely fail to move when I power on the disk, so the controller and
firmware cannot even determine its size. After a few moments the disk spins
down. As I said, this is intermittent, sometimes it will work OK.
A friend has been helping me and he gave me a complete set of the three
boards in the RD53 from a known working disk (he can't give me the disk for
I will pretend I didn't read that...
reasons not worth going into). I changed all three
boards and the drive
still completely fails to move the heads, in fact now the fault seems
permanent. My friend suggested that the positioning coil may be faulty. He
measured the resistance of the coil on one of his working disks (at the plug
that goes to the coil from the motor control board), it came to 3 ohms, mine
also measured 3 ohms. I measured the voltage at the plug going to the coil,
one reads 2V the other 3V, but when it works they both go to about 5V.
I assume you mean the voltage between the pins on the plug, that is the
voltage across the coil.
As I am sure you know, the positioner is simple in concept. It relies on
the magnetic attraiction and replusion between the coil and a fixed
permanent magnet. If there is current through the coil, there must be a
force (I have never heard of a permanent magnet going intermittant!).
You are applying a voltage to the voice coil. Is it the smae polarity in
both cases (is it possible that you are trying to move the heads in the
wrong direction)? I asusme you didn't plug the coil in backwards!).
But even wih the voltage applied, are you sure there's a current? Could
be be something as simple as a back contact at the connector? What about
a hairline crack in the flexpriint to the coil? It may work OK when the
ohmeter is conencted and fail in the operating posiiton (yes I have seen
faults a senaky as that!).
is there any form of head locking device? If so, is it being releaed?
With the disk spinning (essential!), what happend if you 'blip' a DC
supply across the posiitoned coil with the latter disconnected from the
PCB? Do the heads move then?
If you undo the board swap and go back to boards that you know worked on
this drive, do you get it working properly sometimes?
-tony
16 May
16 May
11:10 a.m.
Many thanks for the reply. I am not an electronics expert unfortunately, but
will look at your suggestions. One thing I did (perhaps wrongly) was measure
the voltage with one probe connected to the casing, not to the other pin on
the cable. I will try across the two pins to see what that is like. I don't
have a DC supply I can use to "blip" the coil, unless I can press the PSU
from my MicroVAX II into service for this? Is there a
danger I might pass
too much current and burn the coil?
Regards
Rob
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 16 May 2010 18:37
To: cctalk at classiccmp.org
Subject: Re: RD53 Restoration
I have posted before about an RD53 I am trying to get back to working
order.
After unsticking the heads I thought I had a
working disk as I have
been
able to format it and do an image restore of the
VMS installation
media to
it. However, intermittently it has been failing.
When this happens
the heads
completely fail to move when I power on the disk,
so the controller
and
firmware cannot even determine its size. After a
few moments the disk
spins
down. As I said, this is intermittent, sometimes
it will work OK.
A friend has been helping me and he gave me a complete set of the
three
boards in the RD53 from a known working disk (he
can't give me the
disk for
I will pretend I didn't read that...
reasons not worth going into). I changed all
three boards and the
drive
still completely fails to move the heads, in fact
now the fault seems
permanent. My friend suggested that the positioning coil may be
faulty. He
measured the resistance of the coil on one of his
working disks (at
the plug
that goes to the coil from the motor control
board), it came to 3
ohms, mine
also measured 3 ohms. I measured the voltage at
the plug going to the
coil,
one reads 2V the other 3V, but when it works they
both go to about
5V.
I assume you mean the voltage between the pins on the plug, that is the
voltage across the coil.
As I am sure you know, the positioner is simple in concept. It relies
on
the magnetic attraiction and replusion between the coil and a fixed
permanent magnet. If there is current through the coil, there must be a
force (I have never heard of a permanent magnet going intermittant!).
You are applying a voltage to the voice coil. Is it the smae polarity
in
both cases (is it possible that you are trying to move the heads in the
wrong direction)? I asusme you didn't plug the coil in backwards!).
But even wih the voltage applied, are you sure there's a current? Could
be be something as simple as a back contact at the connector? What
about
a hairline crack in the flexpriint to the coil? It may work OK when the
ohmeter is conencted and fail in the operating posiiton (yes I have
seen
faults a senaky as that!).
is there any form of head locking device? If so, is it being releaed?
With the disk spinning (essential!), what happend if you 'blip' a DC
supply across the posiitoned coil with the latter disconnected from the
PCB? Do the heads move then?
If you undo the board swap and go back to boards that you know worked
on
this drive, do you get it working properly sometimes?
-tony
5334
days inactive
5334
days old
1 comments
2 participants
participants (2)
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ard＠p850ug1.demon.co.uk -
robert.jarratt＠ntlworld.com