Re: vintage disk drive dilema - to modify or not to modify

[Mike Willegal <mike@willegal.net>]

This circuit apparently uses a simple RC time constant to set timing. 
My drive (the initial design) uses a 330pF cap which is charged through 
a 9.1K resistor, as your schematic shows.  A later drive I have, shows 
about 12K total resistance increasing the time about 25%.  Looking at 
the scope shows my original drive doesn't really meet Apple's spec, the 
rise time needs to be extended, similar to what the later drive exhibits.

Regards,
Mike Willegal


Patrick Schaefer wrote:
> Mike Willegal schrieb:
>
> >       I suspect that I could improve this drives performace by 
> > increasing the resitance in the peak detection delay circuit to the 
> > standard that was used in later disk drives.  Most likely adding a 3k 
> > reistor in series with R21 would do the job.  
>
>
> This increases the time constant of the first monoflop. In my schematic, 
> it's 9k1 / 330pF. Is this the 'original' value, or the new one you want 
> to achieve with your modification?
>
> The datasheet values are 6k4 / 200pF.
>
>
> Patrick
>
>
>
> BTW: I would store the vintage drive at a safe place and use something 
> less valuable for daily work...