Teac FD-55B Floppy Oddity

From: John Chris Wren <jcwren_at_jcwren.com>
Date: Wed Mar 6 19:11:14 2002

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
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),
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?

        Thanks very much,
                --John

> -----Original Message-----
> From: owner-classiccmp_at_classiccmp.org
> [mailto:owner-classiccmp_at_classiccmp.org]On Behalf Of Tony Duell
> Sent: Wednesday, February 27, 2002 17:43 PM
> To: classiccmp_at_classiccmp.org
> Subject: Re: Teac FD-55B Floppy Oddity
>
>
> >
> > Indeed, my boards are P/N 15532001-01. Mine doesn't have a
> 7556-00, but a
> > 7358-00. The 48 pin ASIC is the same. U8 is a 6-Unit 320mA Transistor
>
> The quality of printing is so bad, that the 30 pin ASIC could well be
> 7358-00.... I suspect this is the same board.
>
> > Array with Clamp Diode and Strobe, and probably most of it is
> used in the
> > stepper motor driver. They're probably using 1 of the channels
> to pull down
>
> 4 sections for the head stepper, one for head load, one for the front
> panel LED. That LED is not going to take much current -- I guess the
> driver was used 'because it's there'.
>
> > the head solenoid because of it's current capability. The silly
> > Mitsubishians have a dimensional drawing of the part, but no actual
> > datasheet.
>
> The head load section has an input on pin 2, output on pin 15. It's shown
> as a NAND gate on the schematic. One input of all the gates in U8 goes to
> pin one, which is tied high.
>
> On the 1922-00 chip, look at pin 42 (HL output, goes to pin 2 on U8) and
> pin 41 (HOD -- this is the drive to Q4 to apply 12V to the solenoid to
> pull it in). My guess is that pin 42 should essentially follow the head
> load signal from the controller and pin 41 should provide a pull-in pulse
> whenever head load goes from deasserted to asserted.
>
> Q4 is a PNP transistor. Emitter to +12V, collector to the 'top' end of
> the load soleneoid. CR1 (diode) between +5V and the collector (this is to
> provide the +5V holding supply when Q4 is cut off). There's a couple of
> resistors in package RA6 -- seem to be 2k2 each. One from pin 4 to pin 3
> (this is connected between the base and emitter of Q4), the other from
> pin 4 (base of Q4) and pin 5 (to pin 41 on the ASIC). It's all pretty
> simple...
>
> Incidentally, there's a similar circuit for the head stepper motor using
> transisto Q3 nad diode CR3...
>
> -tony
>
>
Received on Wed Mar 06 2002 - 19:11:14 GMT