[cctalk] Re: Diablo Model 40 Series - Disturbed head positioning

What is the purpose of the two microswitches seen in the upper right of the video view? Could one or both of those be intermittent? Have they been tested for continuity/intermittence with an analog VOM? Don Resor -----Original Message----- From: Dominique Carlier via cctalk <cctalk(a)classiccmp.org> Sent: Tuesday, April 30, 2024 8:47 AM To: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org> Cc: Dominique Carlier <dce(a)skynet.be> Subject: [cctalk] Diablo Model 40 Series - Disturbed head positioning 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