How to adjust the speed of floppy drives?

[Ernest <leucoplast@seanet.NOSPAM.com>]

I have a couple of "hacked" disk ][ style drives that are no longer working.
I'm not exactly sure of what the problem is but I think that the speed
adjustments are off. The former owner moved the adjustment pots to the
front of the drive because (according to him) the drives needed to be
adjusted frequently and he was tired of having to take the drives out to
adjust them. The drives also have Write Protect toggle switches and the
red/green lights on the front too (also added by the former owner.) I don't
want to toss the drives out if I can repair them but I'm not sure how best
to do it.

I don't have a strobe light for adjusting them, and they are not able to
read any of the speed utility disks for adjusting the drives by hand. Is
there a way to adjust the drives by small amounts to see if I can finally
get them to read a disk? Can I adjust the drives on the fly, while a disk
is spinning in the drive, or do I have to power down between adjustments? 

Or, does anyone want to adjust the drive speeds for me, for a reasonable
price, if I mail them to you?

Thanks.