The Minolta 9000 AF, besides all its unique qualities, is known for two very common and serious faults caused by aging/detoriation of grease inside the camera:
- aperture release not working reliable any more
- shutter release not working reliable any more
Plesse note that these errors are not a sign of actual wear - even completely mint bodies may be affected by this.
Both faults often start manifesting by sporadic errors (underexposure or not exposed frames, if the shutter fails, or overexposure, if the aperture fails) after long periods without use or storage in hot or otherwise inappropriate climate. The effect may seem to go away - but only for a short while - when using the camera again, but this alone won't repair it - unreliable equipment is useless for any serious work.
While both faults seem to be easy to repair in theory (remove the grease off the electromagnets), in practical terms, they can be considered as fatal faults, since a professional repair will cost about 200 - 300 EUR, and it is almost impossible to fix the camera yourself given the location of these magnets buried deep inside the camera and the required recalibration afterwards.
My backup 9000 AF body suffered from a similarly broken shutter in the early Nineties, and it costed me about 350 DM (ca. 180 EUR) flat to replace the shutter. Four years ago, my third 9000 AF body suffered from a sporadically failing aperture magnet. A repair would have costed ca. 200 EUR today. It took me ca. ten (!) more 9000 AF bodies to finally find a mint 9000 AF body in actually fully working condition again. (All claimed to be in "as new" condition and perfectly working order before the deal, even on explicit request to test this error, so beware!)
The sporadical nature of the error makes it difficult to detect the error when buying used equipment - so, if you buy used 9000 AF bodies, always allow for a significantly long testing period (at least two weeks). A serious seller will grant you this right knowing that a shorter test period will render any tests pointless.
Mind, that playing with the camera may "reset" the period of required "no usage" for the error to occur, so advance the film lever when you receive the camera, and only start actually testing it after the two weeks have passed.
If, without a lens attached, you switch the camera on and tick the aperture lever under these conditions, the aperture hooking mechanism in the bajonett must flip to the other end. Make no mistake, if this does not happen on the very first (!) tick, the aperture release is broken, even if it may work on subsequent tries (as it often does). Note, that the shutter must be loaded for this to work, and if you only load the shutter immediately before testing the aperture mechanism, the movement of gears inside the camera may have covered a sporadially occuring error for a while already. Hence, be sure to advance the shutter before the two weeks of dedicated "idle time".
If this worked out fine, try the shutter: Set the camera to M mode BULB, then fully press and hold the shutter release. The mirror must flip up and the shutter must open without any delay and remain open until you release the button. Remove the camera back and put on the MD-90 motor drive with fresh batteries and in C mode. Point the camera at bright light while looking at the shutter from the backside. Fire sequences of a at least a few hundred shots (you will need to hold the counter reset button so it does not stop after ca. 36 frames). While the camera back has been removed, the shutter will always run at 1/4000s. If - even in a single case - the flash of light through the shutter looks "different", the shutter is broken. In order to be sure it works, try other exposure times as well. Therefore, you will need to manually press down the small contact switch usually pressed down by a needle of a closed camera back. If, after this little torture (which is no torture at all for a professional grade camera body), you see fragments of grease or oil on the shutter blades (check from both sides while manually advancing the film), this is a sign of a potentially nearby fault as well. The blades must be completely free of grease. BTW. In order to check the front side of the shutter blades, it is necessary to flip the mirror up. On the Minolta 9000 AF it is absolutely safe to manually (though very carefully!) flip the mirror up and hold it fixed in the upper position while releasing the shutter (this may not be the case for other bodies, so take care!).
Sorry for the bad news - and good luck to find a replacement...
Greetings,
Matthias