Re: 5.25 Speed Problems

[Rubywand <rubywand@swbell.net>]

william strutts writes ...
> 
> Why would a 5.25" Apple Unidisk drive not be able to
> maintain a constant speed?  Is the controller bad or
> one of the drive motors?  I can get it to speed up and
> I have adjusted the speed so that they appear correct.
> There is one of those 50/60mhz black/white dashed (strobe?)
> charts on the drive wheel.  I adjusted it like  you would
> an old turntable so that the lines look steady when it
> is spinning.  I also tried adjusting the pot using Copy
> II Plus and the speed but the speed wavers up
> and down like from 23 to 233.

     That is an extraordinary variation. Since Copy II+ samples speed by
writing to and reading a diskette in the drive, you may have a diskette which
gets stuck from time to time.

     Or, you may have a diskette to which Copy II can not reliably write. If
the diskette is a high-density (HD) type, it will not work reliably in most
5.25" Apple II drives. You need to use Double Density (DD) diskettes
sometimes called "360K" diskettes.


> I checked my other
> 5.25 drive and it is a solid 200.3 well withing the
> 198 to 230 range specified by Copy II Plus.

     230 would be too slow for most purposes. A correct Copy II Plus reading
for normal use is in the 198 through 202 range.

     If you are using the same diskette to check both drives, there are a few
reasons it may work in one drive but not the other:

1- The 'good' drive may be able to turn a 'sticky' diskette better.

2- The 'good' drive may be a later model 40-track drive which can R/W
high-density diskettes (at least some HD diskettes and at least well enough
to work with the Copy II+ Speed adjustment).

3- The pressure pad may have become dislodged.

4- You mention (below) that you cleaned the heads; so, that is probably not a
variable.



> I also checked the drive pulley but it doesn't appear
> to be worn.  No cracks or anything like that.  There
> doesn't appear to be any way to tighten the pulley any.
> It is an Alps drive mechanism.  Any suggestions or is
> the drive ready for the trash heap?  I also cleaned the
> heads.

     If you get a steady, no-jitter, no-jerk, strobe pattern (using the
visual adjustment method) with the test diskette inserted, then, there is
almost certainly something wrong with R/W to the diskette.

     If the diskette does not seem to be turning steadily, you could try 
wiping the drive pulley and belt with an alcohol cloth (in case oil has
gotten into the works).

     You could check to make sure your pressure pad (which comes down from
the top) has not become dislodged.

     You could try using a different diskette.

     You could examine the drive's circuit board for evidence of blown
components (for example, blown electrolytic capacitors).



Rubywand