Thank you very much for all your great advices! They helped a lot!
If it appears completely dead, try another drive on the machine to understand if another drive works. If you don't have another drive, I would take the affected drive completely apart right down to the little gears and motor. It isn't difficult to do. I believe I came across some youtube video showing a take apart, just go slow and carefully, keep all parts in safe place while taking apart and shoot some photos.
That's exactly that what I'm going to do next. Although I suspect a failure of an electronic component I'd like to get sure that the mechanical part is good.
I believe it might be the motor that died.
There are two motors, one for ejecting the floppy disc and a second for spinning the disc.
There are three motors actually:
- one for ejecting the floppy
- one for moving the heads
- one for spinning the disk
The 1st one is not important for the time being.
I've checked the 2nd motor thoroughly.
It's just a bipolar Minebea 08BJ-H031-41 stepping motor with 4 wires. Each of the two windings has a resistance of approx. 90 Ohms. I was able to manually drive this motor away from the zero track sensor by alternately attaching a 9V battery to the windings and switching the polarity.
After that, I reinstall the drive in the computer, powered it on and pressed on the inject microswitch with a screwdriver. The disk motor started and the head quickly moved to the track 0. So the stepping motor can be considered good.
The spindle motor moving the disk cannot be checked without the complex electronics attached to it (it's PWM driven). I assume it's good, too, because it actually spindles when a disk is inserted or the "disk loaded" microswitch is pressed down (with a screwdriver, for example).
I'll receive another Power Macintosh next week and test the drive with it. For the moment being, I'm thinking about building a test suite based on Arduino or similar. The idea is to power the drive and to send some basic commands to it. Fortunately, the pinout of the IC20 connector is known. Control signals from SWIM III chip are partially documented, too. BMOW, who built the FloppyEmu, knows a lot about the signals involved.
The only problem is that the drive control logic isn't documented. There is no publicly available schematics for it. But there are schematics for earlier models available so the logic can be compared. There are only three ICs on this board: the main controller IC (CXA1503Q, probably a custom controller chip), the spindle motor controller (CX20174, another custom Sony chip) and the stepping motor driver IC (Toshiba TA7774P). The latter is well documented.
I'll try to document my tickling as detailed as possible so someone else (curious like me) could play with these drives as well.
Many thanks!
Cheers
PowerMax
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