FD400 drive troubleshooting

Tony Duell ard at p850ug1.demon.co.uk
Sun Nov 25 17:08:29 CST 2007


>  I got my math wrong. The fellow is also wrong.
> 45/60 = .75.
> 100/.75 = 133.333....
>  If rounded to 133, you get 45.11278195----


Incidentally, I asked a friend wbo is both a classic computer enthusiast 
and a musician if there would he any audible difference between playing 
the record at 45rpm and at 45.11 rpm. He said he didn't believe anyone 
could tell them apart. So I susepct the only people this matters to are 
the audiophools.

Actually I am suprised nobofy has tried to sell said audiophools a 
crytal-controlled lamp to view the strob disk with. Or amybe they have 
and I've not noticed it yet.


>  Still, using Tony's multiple method, 400 dots
> would work fine. It would be a large disk but
> it would work.

It's hardly 'my method'. I certainly don't claim to have invented it, but 
alas I can't find a reference to it. 

I am not sure when stroboscopes were invented, I susepct they pre-date 
electricity, though. Certainly stroboscpinc tuning forks exist -- these a 
tuning forkes with slotted vanes on the tines (they are designed to have 
the extra mass of said vanes, of course)< you view the stroboscopic disk 
(or wahtever) through the slits.

To make this marginally on-topic,such tuning forks were used, at least in 
the UK, to set the speed of teleprinter motors. Creed teleprinters have 
series-wound motors with a governor assembly on the end of the motor, and 
you viewed the black and white stripes on the governor cover through such 
a tuning fork.

Somewhere I have a trleprinter test set (an ATE (manfufacturer) TDMS5 if 
you know about such things). The master oscillator not only drives the 
ring counter that acts as the transmit distributor (the whole thing is 
valved, BTW), but also a neon lamp on the panel. You are supposed to view 
this lamp trhough one of said tuning forks and effectively 'zero beat' 
the bulb agianst the fork to get the oscillator on-frequency.

One other thing to be aware of. The ideal strobosope has very narrow 
flashes of light with larger gaps between them. If you are using a 
'harmonic disk' (or whatever you want to call it), you need to get closer 
to this ideal than for a normal disk (at leat to get a very clear 
pattern). Of coure a real xenon-tube strobe does this, a mains neon bulb 
may not.

-tony



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