Thanks for your response Jon :! The technical documentation is available on Bitsavers here: http://www.bitsavers.org/pdf/diablo/disk/model_40/81603_Diablo4xMaint_Apr75… But also here: https://www.wang2200.org/docs/external/DiabloSeries40DiskDriveFieldLevelMai… I thought like you about the sensors, but here the reverse/forward movements even after unloading the heads lead me to think that the issue is at the level of the circuitry involved in the control of the head positionner linear motor. I would like to be able to follow the diagrams easily, but it is incredibly complex. The only good news is that it is perhaps easily identifiable for those who specifically know the Diablo model 40 series disc drives, in the video we can observe very briefly that these reverse/forward movements start as soon as I press RUN, even before the machine begins to deploy the heads. Precisely here: https://youtu.be/HzzxLnSdEOg?t=4 We could deduce that this is a problem at the very base of what balances the voltages for controlling the linear motor.But even in this case, my limited skills do not allow me to direct my research, which is why I need some advice ;) On 30/04/2024 19:05, Jon Elson via cctalk wrote: > On 4/30/24 10:46, Dominique Carlier via cctalk 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. > > Well, I don't know this particular drive, but I can think of a few > things to check.  Presumably, this drive has some sort of velocity > sensor, either part of the voice coil assembly or the head motion > motor.  It is possible that the velocity sensor has gone bad, or that > a wire to the sensor has broken. > > Another possibility is that the track position encoder has gone bad.  > They often are quadrature optical encoders, and possibly a light bulb > has failed or a photodiode has gone bad or has a broken wire or bad > sensor conditioning circuit. > > If you have drawings for this drive, it should be easy to follow this > circuit.  If not, then you will have to find drawings and tech info.  > Hopefully, bitsavers has what you need. > > Jon >

I also thought about it first, but in the documentation it is clearly explained that during the startup sequence, the deployment of the heads is done at the same time as the spin up, during this deployment the heads are raised, they are normally loaded on disc only after one minute +- after the brush cycle, after the nominal speed is reached. On 30/04/2024 21:38, Jon Elson via cctalk wrote:

Yes the oscilloscope are your eyes and ears for electrons… Marc