Re: 5.25 Speed Problems

[Stephen Shaw <stephen@apple2.org.za>]

The Unidisk does read and write at varying speeds - this was one reason why it
was dropped because of problems trying to repair them!
 
On Mon, 11 Jun 2001 01:50:08 -0500, Rubywand wrote:

> 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

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