Need help with a disk ii speed board

[Mochatea396]

Hello group,
I have a disk ii drive that I can’t set the speed on. I use the Apple dealer disk alignment aid software as I always do. If anyone’s not familiar with this program 0 is in the center representing 300rpm. Either side of the zero will represent positive or negative. It shows a -1500 (which I know is not near accurate). Turning the variable resistor it will jump to +1500. Then bounce back and forth between the two positive and negative extremes without touching the resistor. I’ve replaced the variable resistor, as well as the 3 tantalum capacitors on the board as well as making up a new cable. Turning the potentiometer I can hear the drive IS speeding up and slowing down (It’s clearly not spinning at 1500) but it is responding to adjustments.
Kind of at a loss here now as I hoped changing those things would have corrected the issue.
Any direction would he greatly appreciated.

 

[VERAULT]

So what have you found?

 

[Mochatea396]

Testing the wires in the head I found no continuity to any of the others with my meter on the green wire. I checked the green wire from the connector to the solder point in the head and it shows good. I had another head on my bench that I know is out of alignment. (Thanks to me) and I got it very close with feeler gauges and installed it. The speed is now stabilized at -8 like it should be. The drive formats blanks as well. They don’t boot in other drives which is where the alignment comes in as I knew, but the issue appears to be a bad read write head.