Teac FD-55B Floppy Oddity

From: John Chris Wren <jcwren_at_jcwren.com>
Date: Wed Mar 6 22:44:29 2002

        After I inadverently sent mail to the group instead of you personally, I
was scrolling through something unrelated in the archives of this group, and
ran across this link
http://www.classiccmp.org/mail-archive/classiccmp/1999-03/2078.html that
mentioned a FD55-FB (sometimes I wish Google could be told to ignore certain
punctuation). I tried jumpering 'SM', and voila! A good solid head load!
Neither drive had this jumper installed. I think the only reason the drive
ever booted was because the heads don't unload very hard. Weak spring in
the unload mechanism possibly. I dunno. At any rate, the both drives work
perfectly well. I copied some diskettes back and forth a few times, and a
10th generation copy still verifies.

        I haven't checked out the second Otrona I have yet, but I suspect it may be
the same problem. Someone swapped these drives out, and they appeared to
work. How reliably, who can say?

        The other think I found was that I had 4 screws left over, and damned if I
could figure out where they went. After completely reassembling the unit, I
found I had forgot to put the sheild plate over the lower floppy. This
"protects" the drive electronics from the motherboard. I can say that it's
absolutely necessary on this machine. I thought the second drive was
flakey, since a 2nd generation copy failed to verify several times. Found
the plate behind a box of diskettes, replaced it, and the diskette was
working as a 10th generation copy.

        So at least one happy little Otrona, although the keyboard tends to bounce
a little. Perhaps some usage will clear that up. Tomorrow, I check out the
second one (I *really* like these little machines).

        Thanks to everyone who offered to give or sell me a 360K drive. I may yet
need one for the other machine, but I have a feel that it'll be fine. Also,
thanks to everyone else that offered suggestions about the drives, etc.

        --John

> -----Original Message-----
> From: owner-classiccmp_at_classiccmp.org
> [mailto:owner-classiccmp_at_classiccmp.org]On Behalf Of Tony Duell
> Sent: Wednesday, March 06, 2002 21:37 PM
> To: classiccmp_at_classiccmp.org
> Subject: Re: Teac FD-55B Floppy Oddity
>
>
> >
> > Tony,
> >
> > I'm probing around on the PCB, and here's what I find. Pin
> 42 is staying
> > low, no matter what. Shorting pin 41 to ground causes the head
> to load with
>
> I am puzzled... If pin 42 is alwys low, then there's no way the head can
> ever load (U8 a would be turned off, so the output will be floating, so
> no return path for the load solenoid).
>
> > a nice solid thunk. I'm starting to wonder if the drive *is*
> (or ever was)
> > jumpered correctly. I have HM jumpered (on the block with
> DS0/DS1, etc),
>
> So am I...
>
> > and MX (on that same block). Also jumpered is 'PM', off by
> itself. There
> > are no jumpers on the 2x8 block, which contains labels such as
> 'UR', 'ML',
> > 'HL', 'SM', 'UO', and 'RE'. There seems to be one other label
> on that block
> > that the silkscreen smeared on, and I can't read.
> >
> > If this jumpering sounds reasonable (head load on motor
> start is what I
> > think I want), can you tell me the signal path from the 'HM' jumper to
> > wherever it goes?
>
> It's a bit odd, and as far as I can see (it's getting late, so I might be
> missing something), the jumper config you have can't work.
>
> The motor-on line (pin 16) goes to one side of the HM jumper. The select
> line (common of DS0, DS1, DS2, etc) goes to one side of the HS jumper
> (head load on select, I think). The other sides of those 2 jumpers are
> linked. Makes sesne so far, we'd want this signal to load the head.
> Invert that with U3f (it's now an active high signal). We'll call this
> 'H' for the moment.
>
> Take motor_on again (straight from pin 16). AND it (remeber it's active
> low, so it's really an OR) (U2d) with one side of the ML jumper (also
> puled high by a resistor). ML is not fitted, so the output of UD2 is
> essentially motor on. Now invert that with U3d. Call this 'M'.
>
> Now AND H and M with U2b. So far so good. The only problem is that the
> output of U2b goes to the SM jumper and nowhere else. The other side of
> the SM jumper is pulled down (47K resistor in RA4), then goes to pin 40
> (HSM) of the 1922-00 ASIC. So without the SM jumper fitted, it can't do a
> darn thing.
>
> My schematic has the HM, IU (pin 4 is In Use, not Head Load (which is
> what you get idf the HL jumper is fitted instead)) and SM jumpers drawn
> it. Might be worth fitting at least SM and seeing what happens.
>
>
> -tony
>
>
Received on Wed Mar 06 2002 - 22:44:29 GMT

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