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

From: Lawrence Walker <>
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
> >
> > ciao larry
> >
> >
> -tony
Received on Sun May 31 1998 - 18:55:56 BST

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:31:14 BST