Ressurecting FDDs (was Original IBM PC (was Re: Prices to pa

From: Lawrence Walker <lwalker_at_mail.interlog.com>
Date: Sun May 31 18:55:56 1998

On 29 May 98 at 0:18, Tony Duell wrote:

> > On a related note, I have 3 Atari STs all with failed fdds. Any tips on
> > re-alligning these with-out the rather expensive reallign equipment ? Quite a
>
> Depends on what you mean by 'expensive reallign equipment'. You _may be
> able to do it with just a 'scope (i.e. you don't need an alignment disk),
> but it's not that easy.
>
> What you do is hook up the 'scope (in differential input mode) to the
> outputs of the read amplifier (normally TP1 and TP2 or TPA and TPB, but
> not always). Read a known-good disk, and move the head slightly. Find 2
> points of equal amplitude drop, one on each side of the track, and set
> the head midway between them.
>
> It's better to get the right alignment disk, though
>
 With the current price of fdds so low, it's hard to justify buying something
that I would rarely use.

> > while ago I was able to revive another one by trial and error ,fiddling with
> > the head placement. More blind luck than skill. I've heard that most 3 1/2 fdds
> > will work by reversing the P-S connecter and I picked up a 720k Mitsumi to that
>
> Are you sure? Putting 12V where 5V should go is a bad idea, and I wasn't
> aware that Atari drives had the connector backwards.
>
 Yeah this is pretty well documented in the Atari threads. This isn't true for
all brands however but I've never heard of any voltage conflicts. It's a 4 pin
connecter and I wasn't aware of it also having 12v available on that connecter.
 Apparently most fdd brands will work 720 or 1440 but HD is not available
without a modification, I just got unlucky with the one I bought.

> > end recently to no avail. So rather than throwing away more money I would like
> > to try fixing the ones I have first. I have some test equipment but
> > unfortunately my old Dumont tube scope died the good death. (impossible to
> > find neon current limiter). Any suggestions ?
>
> Do you mean neon current limiter? I've heard of neons being used as
> voltage stabilisers - in fact it was quite common. If one of those has
> failed (which is not common), then you should be able to find one of a
> similar voltage, or use a string of zener diodes to replace it.
>
 It's been a while since I messed with it, but IIRC thats how it was described.
There was one on the X-circuit and another on the Y side. A voltage stabilizer
would make more sense tho. I figured there was likely a newer substitute I
could use but haven't the electronics savvy to do so. I have a son that works
for a major electronics supply company but he was unable to find one. Likely
they only deal with newer part manufacturers and I didn't pursue it with the
resellers.
> >
> > ciao larry
> > lwalker_at_interlog.com
> >
>
> -tony
>
>
>
lwalker_at_interlog.com
Received on Sun May 31 1998 - 18:55:56 BST