Having just adapted a PC power supply to run my Apple, I decided to play Moon Patrol. I had inadvertently let one of my drives fall about 3 cm, but I thought that wasn't enough to ruin my drive. Apparently it was, because it cannot now read disks. Sometimes, the stepper motor doesn't even step. In such cases, it will only move at all in phase 2; when the phase 2 signal is removed, the motor just returns to its previous position.
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allthough that DiskII drives are built like tanks.... LOL.....
they really don't agree with misbehaviour...
There are 3 possible sources for the behaviour that you explain:
a small crack in the ceramic read / write head....
maybe viewable with strong magnifying glass
verification: by scope - no signal or bad signal at pin1 or pin2 at the MC3470 chip.....
solution : replacement of the read / write head sled....(worst case scenario )
a small crack in a solderjoint ....... the most boring point.....
in general not really detectable..... solution: resoldering (*) all joints at analog and motor PCB and
then retesting the entire drive.... (*) resoldering in this term means that all soldering joints must
be re-heated till the solderlead gets fluid again to close the micro crack.....
( least worse case scenario )
damaged wire inside of the steppermotor.....
solution: change and replacement of the stepper motor.....
( medium worst case scenario )
i guess your common with the pages at my site ?
good luck / fate
My last working drive failed due to magic smoke escaping the analog card. There are slight cracks on the 74LS125 and C2. These components are intact on both of my other cards. Could it have something to do with the power supply? I made sure to connect the drive correctly every time.
Edit: Just measured the voltages on my power supply jury-rig, and they are fine. I think at this point that it's just age.
When little indians light up a fire at the PCB to issue smoke signals
it's every time a shortcut ( resulting every time from misaligned cable ! ).....
and it's for sure that the cable was misaligned !
sometimes the user shift left or right and othe times they just leave the rear pinrow blank
( shifting frontwards away from the card )....
and in 99% of such cases it's the 74LS125 that is fried....
but in worst cases - when it was recognized late that the indians got panic -
the user might also have fried the CA3146 or other parts on the PCB....