Yes the oscilloscope are your eyes and ears for electrons… Marc
> On May 1, 2024, at 11:44 PM, Dominique Carlier <d...@skynet.be> wrote: > > 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 >>>
