Hi Marc !
It should be so great if it was just the PSU, everything else is hyper
overkill in terms of complexity but on the multimeter all the voltages
show the correct values, including +15V and -15V (generated from the
+24V and -24V of the power supply).
But is it possible that one of these currents, for example the
stabalized +5V is 'parasitized' ? How can it be diagnosed? With an
oscilloscope I suppose?
The interesting thing now is the lack of emergency retraction of the
heads if the power is cut during RUN mode. There is an unfuse +24V
provided for this purpose but it is present in the power supply. If that
problem is common to the others issues, this leads me to think that
there is an issue at the logical level, in this case the breakdown
hypotheses are unfortunately infinite (summing junction on SO board,
servo positioner, SR board, sensors, ...). If it's not common, it should
be a dead capacitor concerning the emergency retraction of the heads,
and a dead amplifier transistor on the heat sink board dedicated to the
plus/minus (forward/reverse) servo positioner, who knows ?
Dominique
On 2/05/2024 01:38, Curious Marc wrote:
Power supply problem?
Marc
On Apr 30, 2024, at 8:58 AM, Dominique Carlier via cctalk
<cctalk@classiccmp.org> wrote:
Hello everyone
I need your help to identify an issue on my Diablo Model 40 Series. I don't
know where to look, it's so vast !
Here's the problem:
When RUN is activated, the drive begins its spin up and simultaneously deploys the heads (normal)
but instead of stabilizing them, the Head Positioner receives a burst of reverse/forward micro
signals. The heads "vibrate", this creates an audible frequency
"BRRRRRRRRRRRRRRRRRR", and it is infinite, the heads are never loaded and the drive never
reaches READY.
At first I thought that perhaps the track zero sensor was defective or
something of the same order but when I disengage RUN mode, the drive unloads
the heads and they should be in a fixed position, here they continue to
reverse/forward but more slowly than in RUN mode.
Because the heads continues to mess around even in unload mode, this a priori
excludes alignment problems.
Here is a video of that issue:
https://youtu.be/HzzxLnSdEOg
Other information, if I cut the power while the drive is in RUN mode, it does
not do an emergency retraction of the heads, related problem?
I was hoping for a power supply problem but all the voltages and even on the
main board cage seem ok (with a multimeter).
If one of you had already encountered this problem of lack of head
stabilization and continuous reverse/forward on this type of drive?
Thanks !
Dominique
