[Coco] s/sc on os-9 l2

[tim lindner]

On Fri, May 10, 2013 at 6:38 AM, Luis Antoniosi (CoCoDemus)
<retrocanada76 at gmail.com> wrote:
> Do you have a schematic or image of this fix ?

I dont know if any schematic has existed for this fix, but I did find it:

ftp://os9archive.rtsi.com/OS9/OS9_6X09/SYSMODS/SS_Pak_Driver.lzh

It is inside that archive called sspak.txt.

I've attached the file here (the ascii art will need a fixed-width font):

                Speech-Sound Pak 1.78 MHz. Modifications
     This text attempts to explain how to modify the Radio Shack/Tandy
Speech-Sound Pak (catalog numbers 26-3144 and 26-3144A) to work with the COCO3
at 1.78 MHz.
     Please note that the level 1 version 02.00.00 COCO OS-9 SSCPAK driver
doesn't work properly with a modified  Speech-Sound Pak.  Included with this
file should be a new driver (SSPak) and a new descriptor (SSP) which work on
either level 1 or level 2 COCO OS9.  We hope that they are an improvement over
the original drivers!  SSPak and SSP are Public Domain, and source is
included, so feel free to distribute them, or to customize them if you wish.
     The hardware modifications are fairly straightforward, but vary slightly
between the two models (26-3144 & 26-3144A).  Make sure that your Speech-Sound
Pak is one of the Paks described, and that you make the correct modifications.
     Externally, the 26-3144's that we have seen have a Radio Shack label,
while the 26-3144A's have a Tandy label.  Internally, the 26-3144 uses a 2907
transistor and the inductor (marked L1) is in a resistor-style (axial)
package.  The 26-3144A uses a different transistor, and the inductor (also
marked L1) is in a small plastic box.  In both Paks the transistor & inductor
(coil) are close to the post hole in the circuit board.
     It is necessary to change the transistor in order for the Speech-Sound
Pak to work properly in most cases.  We have seen only one unmodified Pak
which worked when the COCO3 was running at 1.78 MHz.  The voltage inverter
circuit used must supply at least -5VDC in order for the output OP-AMPs to
function.  Unfortunately, the transistor used is sensitive to the frequency
input to the circuit.  The input signal used is derived from the bus E clock.
When the COCO3 runs at 1.78 MHz, the circuit typically produces only -2.5VDC,
which is not sufficient for the OP-AMPs.
     The 2N3906 is a PNP transistor.  Looking at the flat face, with the pins
pointing down, the pin out should be Emitter, Base, Collector from left to
right.  The 2N2907 transistor should have the same pin out as the 2N3906.  The
transistor in the 26-3144A Pak should have a pin out of Emitter, Collector,
Base when viewed in the same manner as the 2N3906.  When installing the 2N3906
transistor into a 26-3144A circuit board you must swap the Base and Collector
pins so that they match the original transistor's pin out.
26-3144 Voltage Inverter Transistor Change:
     1) Make note of the 2N2907's pin out & orientation.  Most manufacturers
        should use the same pin out, but its worth checking.
     2) De-solder the 2N2907 transistor & remove it from the Speech-Sound
        Pak circuit board.
     3) Solder a new 2N3906 transistor into the Pak's circuit board.  The
        2N3906 should be oriented the same as the 2N2907 that was removed,
        but again its worth checking the pin out!
26-3144A Voltage Inverter Transistor Change:
     1) Make note of the transistor's pin out & orientation.  Most
        manufacturers should use the same pin out, but its worth checking.
     2) De-solder the transistor & remove it from the Speech-Sound Pak circuit
        board.
     3) Carefully bend a new 2N3906 transistor's base and collector pins so as
        to swap the holes they fit into.  Make sure that they do not touch
        each other or anything else that could cause a short circuit.
     4) Solder the new 2N3906 transistor into the Pak's circuit board.  The
        2N3906 should be oriented the same as the transistor that was removed
        (except 2 pins swapped), but again its worth checking the pin out!
     The other hardware change required alters the clock frequency of the
Pak's micro-controller and sound effects chips.  The Speech-Sound Pak uses a
frequency doubling circuit to provide the clock signal for these ICs.  These
chips use a typical clock of 2 MHz, and the old COCO's clock of .89 MHz was
doubled to provide the Pak's ICs with a 1.78 MHz clock.  This is close enough
to 2 MHz that the Pak runs properly.  However, when the COCO3 runs at 1.78
MHz, this frequency is doubled to 3.56 MHz, which is well above the ideal 2
MHz clock.  We've found that most Paks will work at this speed as long as the
voltage inverter has been modified.  If the clock doubler isn't modified, the
speech synthesizer will sound normal, but the sound effects will be one octave
higher than they should be.  That is, sound effects will not sound as they
should, with the result that software which uses the Pak for sound effects
will probably disappoint you.
     Here's a diagram of the 74LS86 (viewed from above), where the 'D'
represents the notch at the "pin one" end of the chip.  Some chips do not have
a notch to indicate pin 1.  In that case, look for a small indentation
(represented here by the lower case 'o') close to pin 1 to find the
orientation of the chip's pin numbers.  The upper case 'O's represent pins.
 pin 14              pin 9
   !                   !
  +O---O---O---O---O---O---O+
  !                         !
  D         74LS86          !
  !o                        !
  +O---O---O---O---O---O---O+
   !                       !
 pin 1                   pin 7
     Here are two alternatives to fixing the Speech-Sound Pak's clock rate.
The first will limit your Pak to use at 1.78 MHz, unless you restore the Pak
to its original state before using it at .89 MHz.  The second will allow you
to switch the Pak to operate at either .89 MHz or 1.78 MHz.  Both fixes will
work on either the 26-3144 or 26-3144A Speech-Sound Pak.
1.78 Mhz COCO3 Clock Frequency:
     1) Cut the trace leading from the Pak's bus Q signal (card-edge pin 7) to
        pin 9 on the 74LS86.
     2) Connect pin 9 of the 74LS86 to the Pak's ground.
.89/1.78 MHz COCO Switchable Clock Frequency:
     1) Cut the trace leading from the Pak's bus Q signal (card-edge pin 7) to
        pin 9 on the 74LS86.
     2) Connect pin 9 of the 74LS86 to the centre (common) pole of a small
        SPDT (Single Pole Double Throw) switch.
     3) Connect one outside pole of the SPDT switch to the Pak's ground.
     4) Connect the remaining pole of the SPDT switch to the Pak's bus Q
        signal.
     5) Mount the SPDT switch on or in the Pak, wherever its convenient, and
        will not accidentally short to anything.
     We hope that your Speech-Sound Pak modification goes as smoothly and
successfully as ours did (once we figured out the voltage inverter problem it
was all downhill!).  Thanks to Kevin Darling and others who believed that
there was no good reason why it wouldn't work!
     Speech-Sound Pak modification by Bill Boogaart (CIS 72075,615), Mario
Dilallo, and Bruce Isted (CIS 76625,2273).
Radio Shack TM Tandy Corporation, OS-9 TM Microware & Motorola, Inc.