26 Feb
2002
26 Feb
'02
2:55 p.m.
Thanks! Perhaps this will be a start towards debugging it. I do know that
the head load solenoid is on a 2x3 connector, and uses the two end pins.
Three of the remaining 4 pins go to the home position opto sensor, and the 4
is an index pin. But I suspect the overall drive topology is pretty
similiar, and probably uses a +12 load/+5 hold also. I'll check that out.
--John
-----Original Message-----
From: owner-classiccmp(a)classiccmp.org
[mailto:owner-classiccmp@classiccmp.org]On Behalf Of Tony Duell
Sent: Tuesday, February 26, 2002 23:16 PM
To: classiccmp(a)classiccmp.org
Subject: Re: Teac FD-55B Floppy Oddity
My Otronas have FD-55B-01-U drives in them. I thought the
drives were
fried, since they wouldn't work on the Otrona
nor on the PC,
but in dinking
around, I determined that on at least one drive
(and probably
the other),
the head load solenoid is not pulling in. I see
power being
applied, but it
only looks like +5V.
I don't have schematics, and I'm not ready to risk wrecking
the drives
determining the following question: Should the
solenoids pull
in on +5 or
+12? If I'm seeing +5, I suspect the
solenoid driver
transistor could be
I am not sure quite which version my schematic applies to (it says
'FD55(L)' on it), but it appears the head load solenoid pulls in on 12V
and holds on 5V.
The head load solenoid conencts to the 2 pin connector J4. Pin one goes to
the open collector driver (part of U8), and is grounded whenever the
solenoid is 'in'. Pin 2 goes via a diode (CR1) to +5V and via a transistor
(Q4) to +12V. THe idea is that U8 will ground one end of the solenoid and
Q4 will be turned on briefly when the solenoid is to pull in (thus
applying 12V to the solenoid, CR1 being reverse biased now) and then Q4
turns off (U8 still grounds the other end of the solenoid), allowing it
to hold in (5V power suppled via CR1).
cooked. The solenoid coil is intact, as I'm
seeing 44 ohms
across it, out
of circuit. In either case, I don't feel
even the lightest
twitch when it's
supposed to pull in (and the jumper is in place,
for load on
motor select).
If the solenoid is mechanically OK, I'd suspect Q4 (assuming it's the
same circuit). If that's OK, then I guess U6 (a custom logic gate array)
is defective -- it controls the head load circuitry (and a lot of other
things)
-tony